DN42&OneManISP – Confederation, Automation, IPAM and Overlay Network This article does not go into implementation details in depth; it only records the internal network architecture design process and automation ideas. If you need reference code or configuration files, please see iYoRoy-Network/bird2-config: BIRD2 Configuration for iYoRoy Network (AS4242422024, AS205369). The repository contains a significant amount of AI-generated code. This article only borrows the logical layering concept of Underlay/Overlay (base layer/business layer), specifically referring to the separation of address roles, and does not involve tunneling encapsulation technologies such as VXLAN/GRE. TL;DR The entire internal network architecture was refactored. What was originally a horizontally split network based on “DN42 / IANA / WireGuard / BIRD config files” was transformed into a set of infrastructure organised by network intent. The final design can be summarised as: Use WireGuard to carry underlay transport between nodes; Use BGP Confederation instead of OSPF / full-mesh iBGP as the internal routing backbone; Separate node identity and service addresses with Underlay / Overlay; Automatically derive AS, loopback and link-local addresses from Tier / Region / Node ID / Token; Use BGP Large Community to express route origin, propagation scope and export policy; Use Ansible to compile high-level peer intent into WireGuard + BIRD + interface configurations and deploy them automatically. Background In some earlier articles from these two series, we successfully brought up a DN42 AS and an IANA AS, with the same infrastructure carrying traffic for both networks simultaneously. In a previous post, DN42&OneManISP - Troubleshooting OSPF Source Address in a Coexistence Environment - iYoRoy's Develop Diary, there was already some initial separation and isolation for the two networks. However, as the number of nodes grew, manually maintaining the WireGuard and BIRD configuration files for this whole thing became more and more complex. Moreover, public network nodes also needed to interconnect and provide mutual IP transit, so in the end I decided to do a thorough refactoring of this entire internal network. Analysis Problems with the Old Architecture Before the refactoring, DN42 routes between nodes were mutually propagated, using OSPF over WireGuard as the IGP, with full-mesh iBGP on top to carry full routing information between border routers. For IANA traffic, nodes were completely isolated from each other, with each node independently advertising its own /48 IANA IPv6 prefix. To sum up: WireGuard was responsible for tunnels between nodes; OSPF over WireGuard was responsible for the IGP; DN42 border routers ran full-mesh iBGP on top; IANA nodes basically each independently advertised their own public prefixes. This architecture worked well when there were few nodes, but problems started to become apparent as the number of nodes increased: WireGuard, OSPF, and BIRD configurations had to be maintained separately; Adding a new node required changes in multiple places, making it easy to miss something; Routing policies for DN42 and IANA influenced each other, yet the configuration was scattered; Cross-PoP scheduling of IANA prefixes was not natural; Some nodes were only transit nodes but were forced to have an overlay identity; Source address selection, route leaks, and exposure of internal addresses became increasingly difficult to control. Design Goals and BGP Confederation The main goals for this refactoring were: Adding nodes should be simple: ideally, only the node identity and peer relationships need to be described; DN42, IANA and the internal backbone should be able to share infrastructure while remaining policy-isolated from each other; IP addresses should be schedulable resources, not fixed identities of nodes; The internal topology should not leak to external BGP peers; Configurations should be generated from declarative data, not by handwriting lots of repetitive WireGuard/BIRD sessions; The deployment process should be automated. There were also several other, more detailed requirements: Some IANA nodes should be able to carry IP transit for other nodes, using an IANA PoP to advertise public IPs for other nodes; Currently, the IANA AS is maintained jointly by たのしい and myself; we need to coordinate, with some infrastructure needing mutual transit and route tuning; We only have one 44Net IPv4 /24 (sponsored by たのしい); if we want to advertise it, all nodes would need iBGP interconnection and an IGP, otherwise only a single PoP can use it; The IANA AS needs to accept downstreams; Route optimization is needed between IANA PoPs. The previous IANA IPv6 prefix assignment rule followed Continent 3 bits + Region 3 bits + Multi-node within region 2 bits, carving several /48s out of a complete /40. However, due to certain upstream limitations on the number of advertised prefixes, and because such fragmented prefixes are unfavourable for IPAM, we planned to eventually aggregate external advertisements only to the continent level, and then handle more detailed parts via internal iBGP routing. The internal network structure on たのしい's side is BGP Confederation, implemented with a manually simulated approach. Actually, after this analysis, defining the internal network architecture became quite straightforward: the most suitable solution was to switch the internal network to BGP Confederation as well, and then utilise the concept of "BGP as IGP" to advertise /32 and /128 routes within the confederation to handle internal routing. At the same time, because a confederation avoids the split-horizon characteristic of traditional iBGP, it doesn't require strict full-mesh, nor does it need separate iBGP instances, making it very decentralized xD. Furthermore, BGP Confederation can be easily merged with たのしい's infrastructure, requiring only that both sides treat the other's internal ASes as confederation ASes. This solution has another benefit, because the containment relationship of our infrastructure is actually like this: graph subgraph 4242423377 Infrastructure 3377_DN42_PoP[DN42 PoP] 3377_IANA_PoP[IANA PoP] end subgraph 4242422024 Infrastructure 2024_DN42_PoP[DN42 PoP] 2024_IANA_PoP[IANA PoP] end 3377_IANA_PoP <==Cross-Infra Confederation==> 2024_IANA_PoP 3377_DN42_PoP <--> DN42 <--> 2024_DN42_PoP 3377_IANA_PoP <--> IANA <--> 2024_IANA_PoP Our DN42 PoPs and transit are isolated, but the IANA PoPs and transit are interconnected. In the BGP Confederation scenario, we can use filters + BGP (Large) Community to isolate route origins while still exchanging IANA traffic engineering intents, achieving a single standard usable across both infrastructures. Overlay and IPAM In the old design, a node often simultaneously held two identities: It was a router in the network; It was also a service address holder reachable within DN42 / IANA. After the refactoring, I decided to separate these two identities: Underlay: the node's identity as a router, used for internal interconnection, next-hop, tunnels, and forwarding; Overlay: the DN42 / IANA address used when the node provides services to the outside world or accepts traffic. This way, a node can only participate in forwarding without having a DN42 IPv4 address; it can also temporarily announce a certain overlay /32 or /128 when needed. In practical application scenarios, my DN42 address space is not very abundant; I originally registered a /28, with only 16 usable addresses. Some nodes, like IEPL tunnel nodes or IX nodes, only perform forwarding roles, do not need to host services, and do not need to be connected from the outside. Therefore, theoretically they do not need to be assigned independent, reachable DN42/IANA addresses. Moreover, since we had already decided to switch the internal network to BGP Confederation, based on this configuration we could re-plan the originally horizontally split DN42 + IANA network structure into a vertical Underlay + Overlay division. DN42 and IANA addresses/traffic become the payload of the upper-layer Overlay Network, while the lower-layer Underlay Network serves as the infrastructure for underlying communication and forwarding between nodes. In this scenario, IP addresses become resources that can be easily scheduled within the internal network, rather than unique IDs bound to a node. The advantages are clear: Saves scarce address resources: transit nodes can have only an underlay identity, without needing DN42 IPv4 or public addresses; Anycast and address migration: Overlay addresses become resources schedulable via BGP, no longer tightly bound to a specific machine; Hides transit nodes: pure transit nodes do not need to expose globally reachable addresses, making it harder for outsiders to directly probe the internal topology; Easy new node onboarding: new nodes join the underlay first, and overlay addresses are assigned when they need to carry services; Elegant transit delivery: IANA PoPs can deliver customer prefixes or service addresses to other nodes via the internal confederation. Design In summary, the final design consisted of the following IPAM mechanism and automation workflow. Each node possesses some basic metadata: Tier: indicates the node's purpose, e.g., backbone, IX access, or intra-net node Region: the continent region where the node is located ID: the node's ID within that region Token: a random 16-bit string assigned to the node, used as a unique ID for the node under IPv6 For Tier and Region, several tables were created as data sources: Tier Desc 1 Backbone 2 IX 3 Backbone + IX Mixed 9 Node Region Desc 0 Reserved 1 Asia 2 Europe 3 Africa 4 North America 5 South America 6 Oceania 7 Antarctica Confederation AS: 4220240000 – 4220249999 Assignment rule: 422024{tier}{region}{node_id:02d} Where tier indicates the node's purpose, region indicates the area where the node is located, and the last two digits node_id distinguish different nodes within the same region. Underlay IPAM IPv4 Prefix: 100.64.0.0/16 Assignment rule: 100.64.{tier*10 + region}.{node_id}/32 IPv6 Prefix: fd18:3e15:61d0:ffff::/64 Assignment rule: fd18:3e15:61d0:ffff:{tier}:{region}::{node_token}/128 To simplify the automation workflow, I also intended to bring the link-local addresses between WireGuard tunnels under automated management, generating them using the aforementioned Tier, Region, and Token, with the automation scripts generating WireGuard configuration and automatically setting up the tunnel and confederation BGP session. The link-local assignment rule generally follows the normal IPv6 rule: fe80::2024:{tier}:{region}:{node_token}/64 Thus, each node only needs to be assigned its metadata to automatically generate the internal network confederation AS and addresses according to the rules above. Overlay IPAM The DN42 IPv4 part is assigned manually. This part has some historical legacy architecture, and changes need to be merged into the official registry, so I plan to assign it manually. The Underlay IPv6 is itself DN42-reachable; if other DN42 IPv6 addresses need to be allocated, they can simply be advertised on demand. For IANA IPv6, the current design format is to first calculate the continent /43 according to the initially proposed rule, e.g., for Asia: 2a14:7583:f220::/43 Then calculate the /46 based on the region, e.g., for Hong Kong region HKG: 2a14:7583:f224::/46 Next, bits from /46 to /112 are set to zero, and the last 16 bits are filled with the node Token to serve as the node's IANA IPv6 address. For example, one of my backbone nodes in Hong Kong: 2a14:7583:f224::7d89/128 Community Isolation Mechanism In this architecture, BGP Large Community effectively acts as the metadata and control information carried along with a route as it propagates between different modules and infrastructures. Based on this metadata, when we export routes to different external peers we can determine: Does it belong to DN42 or IANA? Is it locally originated, brought in by a downstream, learned from a peer, or learned from an upstream? Can it be exported to other ASes? Is it underlay-only? Does this route need AS prepending? As a concrete example, if the first identifier marks the route origin/destination as DN42 or IANA, all routes permitted to be sent to DN42 will be tagged with: (4242422024, 1, 1) Similarly, all routes destined for IANA will be tagged with: (205369, 1, 1) Within various protocols, this acts as a master switch, controlling whether export should occur. IANA upstream export filter: template bgp iana_upstream_v6 { ... ipv6 { ... import filter { if !iana_filter_default_check() then reject; # basic check remove_confederation_as(); # remove confederation as to prevent external peers from maliciously carrying internal as remove_private_community(); # remove private community to prevent external peers from maliciously manipulating internal routes iana_upstream_add_community(); # tag all routes from IANA with community permitting broadcast in IANA infrastructure accept; }; export filter { if !iana_filter_default_check() then reject; # basic check if !iana_upstream_check_community() then reject; # check community: is this a route destined for IANA / does it carry no-advertise/no-export etc. remove_confederation_as(); # remove confederation as remove_private_community(); # remove private community accept; }; ... }; ... } Where iana_filter_default_check() is used to check prefix length, ROA, whether it is a default route, and other miscellaneous content: function iana_filter_default_check(){ if net ~ [::/0] then return false; if net.len > 48 then return false; if bgp_large_community ~ [(IANA_OWNAS,1,1)] && is_self_iana_v6() then return true; if roa_check(iana_roa_v6, net, bgp_path.last) = ROA_INVALID then return false; return true; } remove_confederation_as(), as the name suggests, removes internal confederation ASes: function remove_confederation_as() {     bgp_path.delete([4220240000..4220249999]); # 4242422024 Infrastructure     bgp_path.delete([4233770000..4233779999]); # 4242423377 Infrastructure } remove_private_community(), as the name suggests, removes internal Communities. The current implementation is very rough and needs detailed refinement later, because some Communities should be open to downstreams, allowing them to use Communities to convey routing intents and perform optimizations, such as prepending AS path, which can be used for route tuning or traffic engineering: function remove_private_community(){     bgp_large_community.delete([(4242422024, *, *)]);     bgp_large_community.delete([(205369, *, *)]); } iana_upstream_add_community(), tags all routes from upstream with the Community allowing circulation in the IANA infrastructure, as well as a route source identifier: function iana_upstream_add_community(){     bgp_large_community.add((205369,1,1));     bgp_large_community.add((205369,2,102)); } Where (205369,2,102) identifies the route as coming from an upstream. Route sources are divided into three types: Upstream, Peer, Downstream/Customer/Self (treated as customer). For these three different types of BGP sessions, the exported routes usually differ: To upstream: we need the upstream to advertise our own prefixes and our downstreams' prefixes, so all routes originating from downstream should be exported to upstream. To downstream: we need to provide network services, so we need to export all routes we know, i.e., routes from upstream, peer, downstream. To peer: peering connections are solely for both parties to access each other's networks, so we must not export each other's upstreams or peers, otherwise it becomes free transit/tunneling. Therefore, only routes from downstream are exported. Correspondingly in the current internal network, routes from peers are tagged (205369,2,101), and routes from downstreams are tagged (205369,2,100). iana_upstream_check_community() checks the route's Community, and based on the principles above, judges whether it should be advertised to upstream: function iana_upstream_check_community(){ if !(bgp_large_community ~ [(205369,1,1)]) then return false; # not permitted for broadcast in IANA infrastructure, reject if bgp_large_community ~ [(205369,65535,65282)] then return false; # no-advertise if bgp_large_community ~ [(205369,65535,65281)] then return false; # no-export if bgp_community ~ [(65535,65281)] then reject; # no-advertise if bgp_community ~ [(65535,65282)] then reject; # no-export if bgp_large_community ~ [(205369,2,0)] then return false; # from internal network, this community is used to identify routes from the internal network that should not be advertised externally, reject here if bgp_large_community ~ [(205369,2,101)] then return false; # from peer, reject advertisement if bgp_large_community ~ [(205369,2,102)] then return false; # from upstream, reject advertisement return true; } Similarly, a similar check mechanism applies to DN42. Based on this mechanism, isolating the DN42 and IANA networks becomes very straightforward. The above is just a general explanation; finer community design and various export policies could be further elaborated, but that would turn into another article on routing policy details. This part actually draws heavily from たのしい’s BGP Communities; after all, both infrastructures need to interoperate, and many community specifications are basically copied. Thanks to たのしい for providing the ideas~ Route Lifecycle Phase 1: Ingress / Import When all external routes enter the system, they first pass through the import filter of the corresponding domain. IANA has three types of sources: upstream; peer / IX; downstream. DN42 also has two main types of sources: regular transit / eBGP peer; IX / route server. In addition, the local machine also originates some routes: underlay loopback; DN42 overlay address; IANA own / anycast address. These routes are tagged with Large Communities upon entering the confederation. All subsequent filters must be adjusted based on this. Phase 2: Core / Intra Confederation After entering the BIRD RIB, routes propagate between nodes via the internal Intra BGP Confederation. Here, Intra Confederation is not just about handling connectivity, but more importantly, allowing internal routes to carry policy information as well. The previous OSPF was great at solving: Where is this loopback? How to reach this next-hop? But it could not convey AS information and policy intents, for example: This route was learned from an IANA peer and must not be exported to another peer; This route is DN42 underlay-only and must never be leaked to eBGP; This route is a downstream customer prefix and can be exported to upstream. All of these are strengths of BGP policy. So moving the internal backbone from OSPF / full-mesh iBGP to confederation-style BGP is essentially upgrading the internal control plane to a "policy-carryable control plane". Phase 3: Egress / Export When a route is about to leave the infrastructure, it passes through the export filter again. Here, based on communities, systemic prevention of route leaks and macro-control like AS prepending can be performed. For example: DN42 underlay routes carry an underlay-only community and thus are not exported to DN42 eBGP; Routes learned from an IANA upstream are not exported to another upstream; Routes learned from an IANA peer are not exported to another peer; Routes learned from a DN42 IX are not exported back to IX; NO_EXPORT / NO_ADVERTISE are respected; Before external export, internal confederation ASes and private communities are removed. In summary, it can be illustrated by this diagram: flowchart LR classDef ext fill:#eef7ff,stroke:#5b8def,stroke-width:1px; classDef local fill:#f5f5f5,stroke:#888,stroke-width:1px; classDef filter fill:#fff3d6,stroke:#d19a00,stroke-width:1px; classDef core fill:#eaf8ea,stroke:#3c9b43,stroke-width:1px; classDef export fill:#fdecec,stroke:#d45a5a,stroke-width:1px; subgraph SRC["Route Source"] direction TB IU["IANA upstream<br/>transit / full routes"] IP["IANA peer / IX"] ID["IANA downstream<br/>customer prefixes"] DT["DN42 transit / eBGP peer"] DX["DN42 IX / route server"] LU["Local underlay loopback<br/>100.64.x.y / fd18:...:ffff"] LO["Local overlay address<br/>DN42 own / IANA own / anycast"] end subgraph INFRA["Bird2-Configuration Infrastructure"] direction LR subgraph IMPORT["Ingress / Import filters"] direction TB IUF["IANA upstream import<br/>tag: 205369:1:1<br/>tag: 205369:2:102"] IPF["IANA peer import<br/>tag: 205369:1:1<br/>tag: 205369:2:101"] IDF["IANA downstream import<br/>AS-SET / path check<br/>tag: 205369:2:100"] DTF["DN42 eBGP import<br/>prefix / ROA / self check<br/>tag: 4242422024:2:101/102"] DXF["DN42 IX import<br/>prefix / ROA check<br/>tag: 4242422024:2:101"] STF["Static origin<br/>underlay / overlay route tags"] end META["Large Community metadata layer<br/>domain + source + scope<br/>internal route API"] subgraph CORE["Internal control plane"] direction TB RIB["BIRD RIB"] CONFED["Intra BGP Confederation<br/>member AS: 422024xxxx<br/>policy: full / default / iana_full / no_iana"] WG["WireGuard underlay transport<br/>link-local next-hop<br/>fwmark policy routing"] UNDERLAY["net_underlay<br/>loopback + table 1142"] OVERLAY["net_overlay<br/>DN42 / IANA service addresses"] end subgraph EGRESS["Egress / Export filters"] direction TB DEXP["DN42 eBGP export<br/>reject underlay-only<br/>respect no-export/no-advertise"] DXEXP["DN42 IX export<br/>reject peer/transit learned routes"] IEXP["IANA upstream / peer export<br/>export local/downstream only<br/>reject peer/upstream learned"] DOWNEXP["IANA downstream export<br/>policy: default / own_only / reject"] KEXP["Kernel export<br/>krt_prefsrc by community"] CLEAN["cleanup before external export<br/>remove confed AS<br/>remove private communities"] end end subgraph DST["Route Destination"] direction TB OD["DN42 peers / transit"] OX["DN42 IX"] OI["IANA upstream / peer"] OC["IANA downstream"] KF["Linux kernel FIB<br/>actual packet forwarding"] end IU --> IUF IP --> IPF ID --> IDF DT --> DTF DX --> DXF LU --> STF LO --> STF IUF --> META IPF --> META IDF --> META DTF --> META DXF --> META STF --> META META --> RIB RIB <--> CONFED CONFED --- WG WG --- UNDERLAY RIB --- OVERLAY RIB --> DEXP RIB --> DXEXP RIB --> IEXP RIB --> DOWNEXP RIB --> KEXP DEXP --> CLEAN --> OD DXEXP --> CLEAN --> OX IEXP --> CLEAN --> OI DOWNEXP --> CLEAN --> OC KEXP --> KF class IU,IP,ID,DT,DX ext; class LU,LO local; class IUF,IPF,IDF,DTF,DXF,STF filter; class META,RIB,CONFED,WG,UNDERLAY,OVERLAY core; class DEXP,DXEXP,IEXP,DOWNEXP,KEXP,CLEAN export; class OD,OX,OI,OC,KF ext; Automation: Compiling Network Intent into Configuration All the above discussion on IPAM, Confederation AS, Underlay/Overlay, and BGP Communities would not truly solve the problem if it still ended up being maintained by hand-written configurations; it would just move the complexity from one form to another. Before this refactoring, adding a new node or peer often required simultaneous changes in many places: WireGuard configuration: interface name, listen port, peer public key, endpoint, allowed IPs BIRD configuration: BGP protocol name, neighbor address, neighbor interface, ASN, import/export filter IPAM-related configuration: loopback, link-local, router id, overlay address Deployment-related configuration: which nodes need rendering, which services need restarting Some special cases: nodes behind NAT, passive peers, special local AS, special filters Logically, these things describe the same thing: a connection belonging to a certain routing domain exists between two nodes. But in manual configuration, they end up scattered across WireGuard, BIRD, network interfaces, systemd/openrc, and other places. If just one field is missed or inconsistent, very strange problems can occur, such as WireGuard being up but BIRD neighbor pointing to the wrong interface; or the link-local being changed, but the peer session still having the old address. So in this refactoring, I didn't want Ansible to just be a tool that "fills YAML into Jinja2 templates". If we simply moved the original hand-written config into templates, we would essentially still be maintaining a pile of low-level configurations, just in a different file format. Since automation was introduced, the input should not be "I want to generate a configuration file that looks like this", but rather: Who is this node? Which tier / region does it belong to? Who does it interconnect with? Does this connection belong to DN42, IANA or Intra? What import/export policy should this connection use? Does it have special constraints like NAT, passive, endpoint override? As for the specific WireGuard interface wording, how the BIRD session is written, what the link-local address is – all these should, as much as possible, be generated by the automation system based on rules. Source of Truth: Node State, Not Config Files The input for this automation is mainly placed in Ansible's host_vars. The variables for each node are no longer just parameters needed for template rendering, but the description of the node's identity in the network. For example, a node will have at least: tier: node tier, e.g., backbone, IX, normal node region: region where the node is located node_id: node number within the same region node_token: a stable 16-bit token used to generate the IPv6 address suffix These fields are used for IPAM address management and identification information within the Confederation (as mentioned earlier, AS calculation and IP address derivation). The advantage of this approach is that when a new node joins, we just need to configure its basic metadata, and all its fundamental identities within the underlay are already determined. This significantly reduces subsequent maintenance effort. If link-local addresses were handwritten in every BIRD session, then any change to a node's token or address rule would require changes on all peers; but if the BIRD neighbor address is automatically derived from the peer node's metadata, it always stays consistent with the source of truth. Domain Intent: Declarative Peer Configuration The most important abstraction in this automation is Domain Intent, which treats the Session and its corresponding WireGuard tunnel binding as a single entity, then partitions them by the network type (DN42/IANA/Intra). Taking an Intra peer as an example, an internal connection fundamentally requires two types of configuration simultaneously: WireGuard interface, to provide the transport tunnel BIRD BGP session, to exchange routes over this tunnel If maintained manually, these two parts easily duplicate the same information: interface name peer node listen port endpoint neighbor interface BGP protocol name import/export policy So we abstract a regular Intra peer into a single peer intent. Simplified, it looks something like this: - node: tyo03-jp interface: intra_tyo03 wireguard: listen_port: 10234 passive: true bgp: protocol: intra_ibgp_tyo03 ipv4: import_policy: full export_policy: full ipv6: import_policy: full export_policy: full This declaration does not directly correspond to a single configuration file, but describes the peer intent: There is an internal connection named intra_tyo03 between the current node and tyo03-jp. This connection uses WireGuard for transport, and establishes an Intra BGP session over it, with BGP policy using full. Afterwards, Ansible automatically renders the corresponding WireGuard and BIRD configuration based on this. Thus, a peer relationship only needs to be described once, and the subsequent low-level configuration is generated automatically. For example, the BIRD neighbor's link-local address does not need to be handwritten; it can be automatically obtained from the peer node's tier / region / node_token. The WireGuard endpoint can also be automatically derived from the peer's ansible_host in the inventory and the peer's return peer listen_port. The biggest advantage of this is avoiding state inconsistency between multiple configuration layers. Automatic Endpoint Derivation and Passive Peers In my internal network architecture, not all nodes have perfectly symmetric public reachability. For example, some nodes / DN42 peers are behind NAT and can only initiate connections; some tunnels require a fixed endpoint as the listener, with the other end initiating. Therefore, the peer intent must support special cases like passive listening. If a peer is not passive, the automation can attempt to read ansible_host from the peer's inventory, combine it with the listen_port declared by the peer, and automatically generate the WireGuard endpoint: endpoint = peer_ansible_host + ":" + peer_return_listen_port If the peer is marked as passive, no endpoint is rendered, allowing the peer to actively initiate the connection. Essentially, the endpoint is determined by "how the peer is accessed" and "which port the peer listens on". These two pieces of information already exist in the inventory and peer intent, so there's no need to duplicate them. Of course, for extremely unusual links, the most basic manual override for the endpoint is retained. The goal of automation is not to eliminate all edge cases, but to make the normal cases require no special handling. Generic Scenarios & Exceptions This is essentially a fallback mechanism for special cases: Legacy tunnels Special internal peers carried over DN42 Nodes behind NAT Temporary workarounds Peers requiring strange BGP parameters Certain sessions needing special local AS Some routes only intended for the IANA domain, not the DN42 domain The final design kept: most regular Intra peers can generate WireGuard + BIRD via domain intent. DN42 peer WireGuard can also be generated from DN42 peer intents. However, some special BIRD sessions, such as those requiring separate local_as or special export policies, can still be explicitly declared using low-level configuration. Before final rendering, Ansible merges the generated configuration and legacy/manual overrides into the final configuration. The benefit is that automation covers 90% of the repetitive and error-prone parts, while still leaving room for the remaining 10% of special cases. Configuration Rendering The entire rendering process can be roughly understood as: flowchart TD A[host_vars: node metadata + domain intent] --> B[materialize domain intent] B --> C[effective_wireguard_interfaces] B --> D[effective_intra_ibgp_sessions] C --> E[render wg-quick configs] D --> F[render BIRD intra sessions] A --> G[render BIRD root / DN42 / IANA modules] A --> H[render underlay / overlay interfaces] E --> I[.rendered-wireguard] F --> J[.rendered] G --> J H --> K[.rendered-network] There are three types of final artifacts: .rendered/: BIRD configuration .rendered-wireguard/: WireGuard configuration .rendered-network/: underlay / overlay dummy interface configuration The BIRD configuration is further divided into several modules, written via Jinja2 templates; the actual overlay network separation is also handled here: root config: global defines, includes, kernel protocol DN42 module: DN42 filters, RPKI, eBGP peers, IX peers IANA module: upstream, downstream, peers, RPKI, static routes Intra module: confederation-style BGP sessions, static routes, internal filters Whether these modules are included is also decided automatically based on data as much as possible. For instance, if a node has no DN42 peers, there's no need to render and include ebgp.conf; no IX sessions, no need to include ix.conf. This reduces empty configurations and meaningless includes, and avoids some nodes failing template rendering due to missing related variables. Validation & Deployment The final deployment process also added some check and validation stages: render BIRD validate BIRD render WireGuard validate WireGuard deploy dummy interfaces deploy WireGuard deploy BIRD BIRD configuration is rendered and validated locally first to catch syntax errors as early as possible. WireGuard configuration is also rendered and validated first to avoid missing keys or generating obviously invalid wg-quick configs. Finally, after all validations pass, the underlying interfaces + WireGuard are deployed, and only then is BIRD uploaded and reloaded. Conclusion I'm exhausted; this article has drained me. Why is narrating this architecture in linear language so difficult? After sorting things out, most of the code was basically written by AI, and the results were decent. If you need a reference, see bird2-config/ansible at dev · iYoRoy-Network/bird2-config. The applicable scenarios for this solution are actually quite narrow; the DN42 + IANA BGP Player scene is really too niche xD. Moreover, a major reason this solution can function properly is that the IANA prefixes and DN42, along with the address ranges chosen for my own internal network, do not conflict at all. If there were address conflicts in the transit segments, one would probably still need to consider proper ISP isolation solutions like VRF/MPLS L3VPN. References: Configure BGP Confederation & Fake Confederation in Bird (Updated 2020-06-07) - Lan Tian @ Blog 浅谈 BGP 中的 Transit（中转）与 Peering（对等互联） | 网络蝙蝠侠部落

Building a Cross-Region K3s Cluster from Scratch - Calico No-Encapsulation CNI # Preface I've actually wanted to play with a K8s cluster for a long time, but always felt that without sufficient knowledge, it would be too difficult to attempt. Recently, I spent some time studying DN42 and routing protocols like BGP and OSPF, and realized that it no longer feels so difficult. So I decisively started with K3s ( The main reason for choosing K3s over K8s is its lightweight nature: low resource requirements, no need to pull a bunch of images for deployment, availability of domestic mirrors… In short, K3s suits my needs better. I'm a beginner just starting to explore K3s, so please go easy on me if I make any mistakes~ # Analysis ## Choosing the CNI Component My current network architecture looks like this: ```mermaid graph TD subgraph ZeroTier Domestic subgraph WDS Gateway <--> VM1 Gateway <--> VM2 end NGB <--> Gateway HFE-NAS <--> Gateway NGB <--> HFE-NAS end subgraph IEPL Global-NIC <==OSPF==> CN-NIC end subgraph ZeroTier Global HKG02 <--> HKG04 TYO <--> HKG04 TYO <--> HKG02 end CN-NIC <--> NGB CN-NIC <--> HFE-NAS CN-NIC <--OSPF--> Gateway Global-NIC <--OSPF--> TYO Global-NIC <--OSPF--> HKG02 Global-NIC <--OSPF--> HKG04 %% Style definition: orange background, bold border to represent routers classDef router fill:#f96,stroke:#333,stroke-width:2px,font-weight:bold; class Global-NIC,CN-NIC,Gateway router; Among this, the WDS node is a Proxmox VE host with multiple VMs underneath. It advertises its VMs' IPv4 prefixes via OSPF. When Hong Kong nodes need to access a VM under the WDS node, they can do so by joining the OSPF internal network to achieve multi-hop reachability. This keeps the encapsulation layer count to only one, so there's no worry about MTU "disappearing act". I plan to create two new VMs under WDS to serve as the master and a node (temporarily called KubeMaster and KubeNode-WDS1). Then HKG04 (temporarily called KubeNode-HKG04) will also join the K3s cluster as a node. The simplest approach would be to use K3s's default Flannel as the CNI. However, Flannel is based on VXLAN, and adding another layer of my existing internal network would lead to the following MTU "disappearing act": Data packet -> Flannel VXLAN encapsulation -> ZeroTier encapsulation -> Physical link The actual usable MTU for inter-container communication would likely be compressed to 1350 or even lower. Therefore, I tried to find a CNI solution that can work directly on top of this internal network, and then I found Calico. As I understand, Calico uses BGP as its underlying routing protocol, supports starting in no-encapsulation (No-Encap) mode, and hands packets directly to the upper routers for routing. Thus, I chose Calico as the CNI component. Routing Design To ensure that intermediate routers know how to route Pod IPs, KubeMaster and KubeNode-WDS1 are under the Proxmox VE host. They need to establish BGP with HKG04 across the entire internal network. This means that every router at each intermediate level must learn the full BGP routes, so that the following routing path can be established: graph LR subgraph WDS KubeMaster KubeNode-WDS1 Gateway end subgraph IEPL CN-Namespace Global-Namespace end KubeNode-WDS1 <--> Gateway KubeMaster <--> Gateway <--> CN-Namespace <--> Global-Namespace <--> HKG04 %% Style definition: highlight nodes with routing capability classDef router fill:#f96,stroke:#333,stroke-width:2px,font-weight:bold; class Gateway,CN-Namespace,Global-Namespace router; Otherwise, any intermediate hop would drop packets because it doesn't recognize the source/destination IP. Also, due to the property of iBGP that routes learned from a neighbor cannot be propagated to the next iBGP neighbor, all BGP sessions between Gateway, CN-Namespace, Global-Namespace and the nodes need to enable Route Reflector; otherwise, nodes cannot correctly learn routes from each other. That said, this architecture would be more suitable for BGP Confederation, but my existing network is already quite complex, and adding BGP confederations would make later maintenance more troublesome. Moreover, my number of nodes is small, so the overhead of iBGP Full Mesh is acceptable. It's definitely not because I'm lazy (so Thus, the final network routing structure is as follows: graph TD subgraph WDS VM1 VM2 Gateway end subgraph IEPL CN-Namespace Global-Namespace end VM1 <-.Calico iBGP Full Mesh.-> VM2 VM1 <--iBGP Route Reflector--> Gateway VM2 <--iBGP Route Reflector--> Gateway <--iBGP--> CN-Namespace <--iBGP--> Global-Namespace <--iBGP Route Reflector--> HKG04 Gateway <--iBGP--> Global-Namespace HKG04 <-.Calico iBGP Full Mesh.-> VM1 VM2 <-.Calico iBGP Full Mesh.-> HKG04 %% Style definition classDef router fill:#f96,stroke:#333,stroke-width:2px,font-weight:bold; %% Mark nodes with routing/forwarding or RR functions as Router class Gateway,CN-Namespace,Global-Namespace router; The dashed-line BGP sessions are automatically created by Calico, while the solid-line parts need to be manually created by us. Keeping Calico's own iBGP Full Mesh is for future scalability, so that nodes can preferentially establish direct P2P connections via ZeroTier instead of taking a detour through the Route Reflector aggregation router. Deployment After clarifying the structure, deployment becomes simple. Enable Kernel Forwarding and Disable rp_filter Standard practice. echo "net.ipv4.ip_forward=1" >> /etc/sysctl.conf echo "net.ipv6.conf.default.forwarding=1" >> /etc/sysctl.conf echo "net.ipv6.conf.all.forwarding=1" >> /etc/sysctl.conf echo "net.ipv4.conf.default.rp_filter=0" >> /etc/sysctl.conf echo "net.ipv4.conf.all.rp_filter=0" >> /etc/sysctl.conf sysctl -p Install K3s Master Because the KubeMaster control plane node is located inside China, it's best to configure image acceleration: mkdir -p /etc/rancher/k3s cat <<EOF > /etc/rancher/k3s/registries.yaml mirrors: docker.io: endpoint: - "https://docker.m.daocloud.io" quay.io: endpoint: - "https://quay.m.daocloud.io" EOF Install using the mirror: curl -sfL https://rancher-mirror.rancher.cn/k3s/k3s-install.sh | \ INSTALL_K3S_MIRROR=cn INSTALL_K3S_EXEC=" \ --flannel-backend=none \ --disable-network-policy \ --cluster-cidr=10.42.0.0/16" sh - Note the need to specify --flannel-backend=none and --disable-network-policy to disable the default CNI component. Use cat /var/lib/rancher/k3s/server/node-token to view the token and record it. Worker Nodes For nodes inside China, configure image acceleration: mkdir -p /etc/rancher/k3s cat <<EOF > /etc/rancher/k3s/registries.yaml mirrors: docker.io: endpoint: - "https://docker.m.daocloud.io" quay.io: endpoint: - "https://quay.m.daocloud.io" EOF Then install K3s using the mirror and join the cluster: export INSTALL_K3S_MIRROR=cn export K3S_URL=https://<master node IP>:6443 # Replace with your master node's actual IP export K3S_TOKEN=K10...your token...::server:xxx # Replace with the full token obtained in the first step curl -sfL https://rancher-mirror.rancher.cn/k3s/k3s-install.sh | sh - At this point, the status of each node should be NotReady because the CNI component is missing. Install Calico and Configure No-Encap Mode On the master, manually download https://raw.githubusercontent.com/projectcalico/calico/v3.26.1/manifests/tigera-operator.yaml and install the Calico operator: kubectl create -f tigera-operator.yaml Configure a custom resource by creating a custom-resource.yaml file: apiVersion: operator.tigera.io/v1 kind: Installation metadata: name: default spec: # Add image registry configuration registry: quay.m.daocloud.io calicoNetwork: ipPools: - blockSize: 26 cidr: 10.42.0.0/16 encapsulation: None natOutgoing: Enabled nodeSelector: all() Here, specify encapsulation: None to enable No-Encap mode. You can also modify the IPv4 CIDR here if needed. Then: kubectl apply -f custom-resource.yaml to perform the installation. Use: kubectl get pods -A -o wide to check Pod status, waiting for each node to finish pulling images. Configure BGP Topology Label Nodes Label nodes to specify that nodes under WDS connect to the Gateway's BGP in the WDS node, and nodes outside China connect to the BGP of the Global Namespace: kubectl label nodes kubemaster region=WDS kubectl label nodes kubenode-wds-1 region=WDS kubectl label nodes kubenode-hkg04 region=Global Calico Configuration Create a YAML configuration file: apiVersion: crd.projectcalico.org/v1 kind: BGPPeer metadata: name: route-reflector-domestic spec: nodeSelector: region == 'Domestic' # This part is not actually used; I originally designed a general aggregation router in the Domestic area peerIP: 100.64.0.108 asNumber: 64512 --- apiVersion: crd.projectcalico.org/v1 kind: BGPPeer metadata: name: route-reflector-wds spec: nodeSelector: region == 'WDS' peerIP: 192.168.100.1 asNumber: 64512 --- apiVersion: crd.projectcalico.org/v1 kind: BGPPeer metadata: name: route-reflector-global spec: nodeSelector: region == 'Global' peerIP: 100.64.1.106 asNumber: 64512 This means: All nodes with label region equal to Domestic will have a BGP session to 100.64.0.108 (the domestic aggregation router) using AS 64512 All nodes with label region equal to WDS will have a BGP session to 192.168.100.1 (the Gateway for all VMs under the WDS node) using AS 64512 All nodes with label region equal to Global will have a BGP session to 100.64.1.106 (the overseas aggregation router) using AS 64512 This achieves what is shown in the diagram: all VMs under the WDS node, including the master and KubeNode-WDS1, connect to the Gateway aggregation router of the WDS node, and all nodes in overseas areas connect to the overseas aggregation router. Configure Aggregation Router iBGP This part is simply a matter of writing Bird configuration files (easy). Here are a few examples: k3s/ibgp.conf: function is_insider_as(){ if bgp_path.len > 0 && !(bgp_path ~ [= 64512 =]) then { return false; } if net ~ [ 10.42.0.0/16{16,32} ] then { return true; } return false; } template bgp k3sbackbone{ local as K3S_AS; router id INTRA_ROUTER_ID; neighbor as K3S_AS; ipv4{ table intra_table_v4; import filter{ if is_insider_as() then accept; reject; }; export filter{ if is_insider_as() then accept; reject; }; next hop self; extended next hop; }; ipv6{ table intra_table_v6; import filter{ if is_insider_as() then accept; reject; }; export filter{ if is_insider_as() then accept; reject; }; next hop self; }; }; template bgp k3speers{ local as K3S_AS; neighbor as K3S_AS; router id INTRA_ROUTER_ID; rr client; rr cluster id INTRA_ROUTER_ID; ipv4{ table intra_table_v4; import filter{ if is_insider_as() then accept; reject; }; export filter{ if is_insider_as() then accept; reject; }; next hop self; }; ipv6{ table intra_table_v6; import filter{ if is_insider_as() then accept; reject; }; export filter{ if is_insider_as() then accept; reject; }; next hop self; }; }; include "ibgpeers/*"; ibgpeers/backbone-cn.conf: protocol bgp 'k3s_backbone_cn_v4' from k3sbackbone{ neighbor fd18:3e15:61d0:cafe:f001::1; }; ibgpeers/master.conf: protocol bgp 'k3s_master_v4' from k3speers{ neighbor 192.168.100.251; }; Main points: it's best not to enable Route Reflector between the aggregation routers, and remember to enable next hop self. After everything is done, using kubectl get nodes should show all nodes as Ready: NAME STATUS ROLES AGE VERSION kubemaster Ready control-plane 2d23h v1.34.5+k3s1 kubenode-hkg04 Ready <none> 11h v1.34.6+k3s1 kubenode-wds-1 Ready <none> 2d7h v1.34.5+k3s1 Use kubectl get pods -A -o wide to view Pods: NAMESPACE NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES calico-system calico-kube-controllers-64fc874957-6bdlz 1/1 Running 0 5h38m 10.42.253.136 kubenode-hkg04 <none> <none> calico-system calico-node-2qz82 1/1 Running 0 4h24m 10.2.5.7 kubenode-hkg04 <none> <none> calico-system calico-node-dhl2c 1/1 Running 0 4h24m 192.168.100.251 kubemaster <none> <none> calico-system calico-node-nbpkj 1/1 Running 0 4h23m 192.168.100.252 kubenode-wds-1 <none> <none> calico-system calico-typha-7bb5db4bdc-rfpwg 1/1 Running 0 5h38m 10.2.5.7 kubenode-hkg04 <none> <none> calico-system calico-typha-7bb5db4bdc-rwwr5 1/1 Running 0 5h38m 192.168.100.251 kubemaster <none> <none> calico-system csi-node-driver-jglwp 2/2 Running 0 5h38m 10.42.64.68 kubenode-wds-1 <none> <none> calico-system csi-node-driver-jqjsc 2/2 Running 0 5h38m 10.42.253.137 kubenode-hkg04 <none> <none> calico-system csi-node-driver-vk26s 2/2 Running 0 5h38m 10.42.141.16 kubemaster <none> <none> kube-system coredns-695cbbfcb9-8fx4p 1/1 Running 1 (7h27m ago) 2d23h 10.42.141.14 kubemaster <none> <none> kube-system helm-install-traefik-crd-5bkwx 0/1 Completed 0 2d23h <none> kubemaster <none> <none> kube-system helm-install-traefik-m9fgj 0/1 Completed 1 2d23h <none> kubemaster <none> <none> kube-system local-path-provisioner-546dfc6456-dmn4g 1/1 Running 1 (7h27m ago) 2d23h 10.42.141.15 kubemaster <none> <none> kube-system metrics-server-c8774f4f4-2wkwh 1/1 Running 1 (7h27m ago) 2d23h 10.42.141.12 kubemaster <none> <none> kube-system svclb-traefik-999cddce-hpmcm 2/2 Running 6 (7h26m ago) 11h 10.42.253.134 kubenode-hkg04 <none> <none> kube-system svclb-traefik-999cddce-q4225 2/2 Running 2 (7h27m ago) 2d22h 10.42.141.9 kubemaster <none> <none> kube-system svclb-traefik-999cddce-xmd64 2/2 Running 2 (7h26m ago) 2d6h 10.42.64.66 kubenode-wds-1 <none> <none> kube-system traefik-788bc4688c-vbbhj 1/1 Running 1 (7h27m ago) 2d22h 10.42.141.13 kubemaster <none> <none> tigera-operator tigera-operator-6b95bbf4db-vl46l 1/1 Running 1 (7h27m ago) 2d23h 192.168.100.251 kubemaster <none> <none> Use kubectl exec -it -n calico-system <calico-node-xxxx> -- birdcl s p to check the status of Bird: root@KubeMaster:~/kube/calico# kubectl exec -it -n calico-system calico-node-2qz82 -- birdcl s p Defaulted container "calico-node" out of: calico-node, flexvol-driver (init), install-cni (init) BIRD v0.3.3+birdv1.6.8 ready. name proto table state since info static1 Static master up 08:58:17 kernel1 Kernel master up 08:58:17 device1 Device master up 08:58:17 direct1 Direct master up 08:58:17 Mesh_192_168_100_251 BGP master up 08:58:33 Established Mesh_192_168_100_252 BGP master up 08:59:00 Established Node_100_64_1_106 BGP master up 12:57:44 Established ip r shows the system routing table: root@KubeMaster:~/kube/calico# ip r default via 192.168.100.1 dev eth0 proto static 10.42.64.64/26 proto bird nexthop via 192.168.100.1 dev eth0 weight 1 nexthop via 192.168.100.252 dev eth0 weight 1 blackhole 10.42.141.0/26 proto bird 10.42.141.9 dev caliac6501d3794 scope link 10.42.141.12 dev calib07c23291bb scope link 10.42.141.13 dev caliab16e60bd19 scope link 10.42.141.14 dev calid5959219080 scope link 10.42.141.15 dev cali026d8f1ddb7 scope link 10.42.141.16 dev califa657ba417a scope link 10.42.253.128/26 via 192.168.100.1 dev eth0 proto bird 192.168.100.0/24 dev eth0 proto kernel scope link src 192.168.100.251 Ping a Pod's IP – if everything is fine, it should work directly: root@KubeMaster:~/kube/calico# ping 10.42.253.137 PING 10.42.253.137 (10.42.253.137) 56(84) bytes of data. 64 bytes from 10.42.253.137: icmp_seq=1 ttl=60 time=33.7 ms 64 bytes from 10.42.253.137: icmp_seq=2 ttl=60 time=33.5 ms ^C --- 10.42.253.137 ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 1002ms rtt min/avg/max/mdev = 33.546/33.632/33.718/0.086 ms Tune MTU This step is actually for stability…? Tests have shown that although my ZeroTier MTU is 1420, packets start to fragment around 1392 bytes (test with ping -M do -s <packet size> <Pod_IP>). Therefore, force the Pod MTU to 1370: root@KubeMaster:~/kube/calico# cat patch-mtu.yaml apiVersion: operator.tigera.io/v1 kind: Installation metadata: name: default spec: calicoNetwork: mtu: 1370 nodeAddressAutodetectionV4: firstFound: true root@KubeMaster:~/kube/calico# kubectl apply -f patch-mtu.yaml installation.operator.tigera.io/default configured

DN42 - Ep.4 Configuring BGP Communities Foreword I am a novice in BGP. This article may contain imprecise content/naive understandings/elementary mistakes. I kindly ask the experts to be lenient. If you find any issues, you are welcome to contact me via email, and I will correct them as soon as possible. If you find this unacceptable, it is recommended to close this article now. What are BGP Communities? TL;DR: BGP Communities "tag" routes, allowing others to use these tags for route optimization. This concept might be unfamiliar to newcomers (like me), who might not initially understand its purpose. Simply put, BGP Communities are a mechanism for tagging routes, similar to adding labels. They allow network administrators to attach one or more "tags" (i.e., community values) to routes propagated via BGP. These tags themselves do not alter the route's path attributes (like AS_PATH, LOCAL_PREF, MED, etc.), but they provide a signaling mechanism to indicate what policy or processing should be applied to that route by other routers within the same AS or in downstream peer ASes. BGP Communities can be used to: Simplify Policy Configuration: Routers inside the network or in downstream ASes only need to configure policies based on community values (like setting LOCAL_PREF, adding NO_EXPORT, applying route-maps, etc.), without needing to know the specific prefix details. This makes policies more centralized, easier to manage, and less prone to errors. Convey Policy Intent to Downstream ASes: An AS can attach community values to routes it advertises to its downstream customer or peer ASes. These communities convey requirements or suggestions on how these routes should be handled, such as route optimization based on geographic location, latency, or bandwidth. Coordinate Policies within an AS: Inside a large AS, when using IBGP full-mesh or route reflectors, edge routers (receiving EBGP routes or redistributing routes) can tag routes with community values. Core routers or route reflectors within the AS can recognize these communities and apply corresponding internal policies (like setting LOCAL_PREF, MED, deciding whether to advertise to certain IBGP peers, adding other communities, etc.), without needing complex prefix-based policies on every internal router. DN42 has its own set of Communities specifications. For details, please refer to: BGP-communities - DN42 Wiki Configuration The general idea and approach in this article are largely based on Xe_iu's method, focusing on adding BGP Communities for geographic information and performing route optimization. Generally, this is sufficient. (Another reason is that I haven't fully grasped the others yet) Note: We should ONLY add geographic information-related BGP Communities to routes originating from our own AS. We should not add such entries to routes received from neighbors. Adding our own regional Communities to a neighbor's routes constitutes forging the route origin, potentially leading to route hijacking. Downstream networks might misjudge the traffic path, routing traffic that should be direct through your network, increasing latency and consuming your network's bandwidth. (Large Communities are an exception, as they have a verification mechanism to prevent this, but that's beyond the scope of this article). The idea is clear. When exporting routes, we first need to verify if it's our own route. If it is, we add the communities tag to the route. The sample configuration provided by DN42 already includes two functions, is_self_net() and is_self_net_v6(), to check if a route is our own. Therefore, writing the configuration part is straightforward. Adding Communities to Routes First, we need to define the geographic region information for the current node at the beginning of the node configuration file. Please check BGP-communities - DN42 Wiki for details: define DN42_REGION = 52; # 52 represents East Asia define DN42_COUNTRY= 1344; # 1344 represents Hong Kong Please modify these values according to your node's actual geographic location. Then, modify the export filter in the dnpeers template: }; export filter { - if is_valid_network() && source ~ [RTS_STATIC, RTS_BGP] then accept; + if is_valid_network() && source ~ [RTS_STATIC, RTS_BGP] then{ + if (is_self_net()) then { # Check if it's our own route + bgp_community.add((64511, DN42_REGION)); # Add continent-level region info + bgp_community.add((64511, DN42_COUNTRY)); # Add country/region info + } + accept; + } reject; }; import limit 1000 action block; During export, it checks if it's our own route. If it is, it sets the bgp_community according to the defined DN42_REGION and DN42_COUNTRY. Here, 64511 is the reserved public AS number identifier specifically for geographic tags (Region/Country); you can just copy it. Apply the same method to the IPv6 export rules, but replace is_self_net() with is_self_net_v6(). Route Optimization Based on Communities Here we need to introduce another concept: local_pref (Local Preference). It is used within an AS to indicate the priority of a route. Its default value is 100, and a higher value indicates higher priority. Furthermore, in BGP route selection logic, local_pref has the highest priority, even higher than AS_PATH length. This means that by setting local_pref, we can adjust the priority of routes to achieve route optimization. Combining this with the BGP Communities mentioned above, we can set the corresponding local_pref based on Communities for optimization. Also, since BGP.local_pref is propagated within the AS, we need to modify the import logic for both eBGP and iBGP routes. My logic for handling BGP.local_pref here references (basically copies) Xe_iu's approach: For routes from the same region, priority +10 For routes from the same country, priority +5 additionally For routes received via direct peering with us, priority +20 additionally Create a function to calculate the priority: function ebgp_calculate_priority() { int priority = 100; # Base priority # Same region detection (+10) if bgp_community ~ [(64511, DN42_REGION)] then priority = priority + 10; # Same country detection (+5) if bgp_community ~ [(64511, DN42_COUNTRY)] then priority = priority + 5; # Direct eBGP neighbor detection (+20) if bgp_path.len = 1 then priority = priority + 20; return priority; } Then, in the import filter within the dnpeers template, set bgp_local_pref to the value calculated by the function: template bgp dnpeers { local as OWNAS; path metric 1; ipv4 { import filter { if is_valid_network() && !is_self_net() then { if (roa_check(dn42_roa, net, bgp_path.last) != ROA_VALID) then { print "[dn42] ROA check failed for ", net, " ASN ", bgp_path.last; reject; } + bgp_local_pref = ebgp_calculate_priority(); accept; } reject; }; Apply the same method for IPv6. After running birdc configure, we should be able to see that our routes have been tagged with Communities labels at our neighbors: (Screenshot source:https://lg.milu.moe/route_all/hk/172.20.234.224) Special thanks to Nuro Trace and Xe_iu. They helped deepen my understanding of BGP Communities and provided much assistance. Reference Articles: [DN42] bird2的配置文件 – Xe_iu's Blog | Xe_iu的杂物间 [DN42] 谈一谈如何配置 BGP community – Xe_iu's Blog | Xe_iu的杂物间 BGP-communities - DN42 Wiki

DN42 - Ep.2 Building Internal Network with OSPF and Enabling iBGP Foreword I am a novice in BGP. This article may contain imprecise content/naive understandings/elementary mistakes. I kindly ask the experts to be lenient. If you find any issues, you are welcome to contact me via email, and I will correct them as soon as possible. If you find this unacceptable, it is recommended to close this article now. Article Update Log {timeline} {timeline-item color="#50BFFF"} July 22, 2025: First edition published, using VXLAN over WireGuard tunnel. {/timeline-item} {timeline-item color="#50BFFF"} July 25, 2025: Updated tunneling solution, using type ptp; to support OSPF traffic via WireGuard (Special thanks to Nuro Trance for the guidance!). {/timeline-item} {timeline-item color="#50BFFF"} August 8, 2025: Added explanation and configuration for iBGP. {/timeline-item} {timeline-item color="#4F9E28"} August 27, 2025: Updated node topology diagram. {/timeline-item} {/timeline} Why Do We Need Internal Routing? As the number of nodes increases, we need a proper way to handle internal routing within our AS (Autonomous System). BGP only handles routing to different ASes, which causes a problem: if nodes A and B are both peering with external networks, a request from node A may have its response routed to node B, even though they are part of the same AS. Without internal routing, node A will not receive the reply. To solve this, we need to ensure that all devices within our AS can communicate with each other. The common solutions are: Using network tools like ZeroTier: Simple to set up, just install the client on each node for P2P connectivity. Using P2P tools like WireGuard to manually create $\frac{n(n-1)}{2}$ tunnels, which works like the first solution but becomes cumbersome as nodes grow. Using WireGuard to establish $\frac{n(n-1)}{2}$ tunnels, then using an internal routing protocol like OSPF or Babel to manage the routing. This is more flexible and easier to scale, but it can be risky and could break the DN42 network due to misconfigurations. Thus, I decided to take the risk. Node Topology graph LR A[HKG<br>172.20.234.225<br>fd18:3e15:61d0::1] B[NKG<br>172.20.234.226<br>fd18:3e15:61d0::2] C[TYO<br>172.20.234.227<br>fd18:3e15:61d0::3] D[FRA<br>172.20.234.228<br>fd18:3e15:61d0::4] E[LAX<br>172.20.234.229<br>fd18:3e15:61d0::5] B <--> A C <--> A A <--> E A <--> D C <--> D C <--> E D <--> E Update Bird2 to v2.16 or Above To use IPv6 Link-Local addresses to transmit IPv4 OSPF data, Bird v2.16 or later is required. Here are the steps to update: sudo apt update && sudo apt -y install apt-transport-https ca-certificates wget lsb-release sudo wget -O /usr/share/keyrings/cznic-labs-pkg.gpg https://pkg.labs.nic.cz/gpg echo "deb [signed-by=/usr/share/keyrings/cznic-labs-pkg.gpg] https://pkg.labs.nic.cz/bird2 $(lsb_release -sc) main" | sudo tee /etc/apt/sources.list.d/cznic-labs-bird2.list sudo apt update && sudo apt install bird2 -y Tunnel Configuration [Interface] PrivateKey = <Local WireGuard Private Key> ListenPort = <Listen Port> Table = off Address = <IPv6 LLA>/64 PostUp = sysctl -w net.ipv6.conf.%i.autoconf=0 [Peer] PublicKey = <Peer Public Key> Endpoint = <Peer Public Endpoint> AllowedIPs = 10.0.0.0/8, 172.20.0.0/14, 172.31.0.0/16, fd00::/8, fe00::/8, ff02::5 ff02::5is the OSPFv3 router-specific link-local multicast address and should be included in AllowedIPs. If you're using Bird versions earlier than v2.16, you'll need to add an IPv4 address for the tunnel as well. See the example below: {collapse} {collapse-item label="WireGuard Configuration Example with IPv4"} [Interface] PrivateKey = <Local WireGuard Private Key> ListenPort = <Listen Port> Table = off Address = <IPv6 LLA>/64 PostUp = ip addr add 100.64.0.225/32 peer 100.64.0.226/32 dev %i PostUp = sysctl -w net.ipv6.conf.%i.autoconf=0 [Peer] PublicKey = <Peer Public Key> Endpoint = <Peer Public Endpoint> AllowedIPs = 10.0.0.0/8, 172.20.0.0/14, 100.64.0.0/16, 172.31.0.0/16, fd00::/8, fe00::/8, ff02::5 Please replace 100.64.0.225 and 100.64.0.226 with your local and peer IPv4 addresses, and remember to add AllowedIPs. {/collapse-item} {/collapse} Enable OSPF You should have already configured basic Bird settings as described in the previous article. Create a new file called ospf.conf under /etc/bird and add the following: protocol ospf v3 <name> { ipv4 { import where is_self_net() && source != RTS_BGP; export where is_self_net() && source != RTS_BGP; }; include "/etc/bird/ospf/*"; }; protocol ospf v3 <name> { ipv6 { import where is_self_net_v6() && source != RTS_BGP; export where is_self_net_v6() && source != RTS_BGP; }; include "/etc/bird/ospf/*"; }; Theoretically, OSPF v2 should be used for handling IPv4, but since we need to communicate IPv4 using IPv6 Link-Local addresses, we are using OSPF v3 for IPv4 in this case as well. The filter rules ensure that only routes within the local network segment are allowed to propagate through OSPF, and routes from external BGP protocols are filtered out. Never use import all; export all; indiscriminately, as this could lead to route hijacking and affect the entire DN42 network. OSPF should only handle internal network routes. {collapse} {collapse-item label="Example"} /etc/bird/ospf.conf protocol ospf v3 dn42_iyoroynet_ospf { ipv4 { import where is_self_net() && source != RTS_BGP; export where is_self_net() && source != RTS_BGP; }; include "/etc/bird/ospf/*"; }; protocol ospf v3 dn42_iyoroynet_ospf6 { ipv6 { import where is_self_net_v6() && source != RTS_BGP; export where is_self_net_v6() && source != RTS_BGP; }; include "/etc/bird/ospf/*"; }; {/collapse-item} {/collapse} Next, create the /etc/bird/ospf folder and then create an area configuration file (e.g., /etc/bird/ospf/backbone.conf) with the following content: area 0.0.0.0 { interface "<DN42 dummy interface>" { stub; }; interface "<wg0 interface>" { cost 80; # Modify according to your network situation type ptp; }; interface "<wg1 interface>" { cost 100; # Modify according to your network situation type ptp; }; # Continue for other interfaces }; The 0.0.0.0 area represents the backbone network. he dummy interface here refers to the DN42 virtual interface mentioned in the previous article The cost value is typically used for cost calculation but in DN42's case, where bandwidth is less critical but latency is more important, you can directly assign the latency value. OSPF will automatically choose the route with the lowest cost (sum of the cost values). {collapse} {collapse-item label="Example"} /etc/bird/ospf/backbone.conf area 0.0.0.0 { interface "dn42" { stub; }; interface "dn42_hkg" { cost 80; type ptp; }; interface "dn42_hfe" { cost 150; type ptp; }; interface "dn42_lax"{ cost 100; type ptp; }; }; {/collapse-item} {/collapse} Finally, open /etc/bird/bird.conf and add the following to include the OSPF configuration file at the end: include "ospf.conf"; Run birdc configure, and then birdc show protocols should show the OSPF status as Running. If not, check the configuration steps for errors. At this point, you should be able to ping between two non-directly connected machines: Enable iBGP Before establishing multiple peer connections, each of your nodes must first have complete knowledge of the internal AS topology. This involves configuring another key component: internal BGP (iBGP). Necessity of iBGP iBGP ensures that all routers within the AS have complete knowledge of external destination routes. It ensures that: Internal routers can select the best exit path. Traffic is correctly routed to the boundary routers responsible for specific external networks. Even if there are multiple boundary routers connected to the same external network, internal routers can choose the best exit based on policies. Compared to using a default route pointing to the border router within the AS, iBGP provides precise external route information, allowing internal routers to make more intelligent forwarding decisions. Disadvantages and Solutions To prevent uncontrolled propagation of routing information within the AS, which could cause loops, an iBGP router will not readvertise routes learned from one iBGP neighbor to other iBGP neighbors. This necessitates that traditional iBGP requires a full mesh of iBGP neighbor relationships between all iBGP-running routers within the same AS. (You still need to establish $\frac{n(n+1)}{2}$ connections , there's no way around it. But configuring iBGP is still easier than configuring tunnels after OSPF is set up ). Solutions include: Using a Route Reflector (RR): An RR router manages all routing information within the entire AS. The disadvantage is that if the RR router fails, the entire network can be paralyzed (which is not very Decentralized). Using BGP Confederation: This involves virtually dividing the routers within the AS into sub-ASes, treating the connections between routers as eBGP, and finally stripping the internal AS path information when advertising routes externally. I haven't tried the latter two solutions. Here are some potentially useful reference articles. This article focuses on the configuration of iBGP. DN42 Experimental Network: Intro and Registration (Updated 2022-12) - Lan Tian @ Blog Configure BGP Confederation & Fake Confederation in Bird (Updated 2020-06-07) - Lan Tian @ Blog Writing the iBGP Configuration File Create a new file ibgp.conf in /etc/bird and fill it with the following content: template bgp ibgpeers { local as OWNAS; ipv4 { import where source = RTS_BGP && is_valid_network() && !is_self_net(); export where source = RTS_BGP && is_valid_network() && !is_self_net(); next hop self; extended next hop; }; ipv6 { import where source = RTS_BGP && is_valid_network_v6() && !is_self_net_v6(); export where source = RTS_BGP && is_valid_network_v6() && !is_self_net_v6(); next hop self; }; }; include "ibgp/*"; The import and export filters ensure that iBGP only processes routes learned via the BGP protocol and filters out IGP routes to prevent loops. next hop self is required. It instructs BIRD to rewrite the next hop to the border router's own IP address (instead of the original external next hop) when exporting routes to iBGP neighbors. This is because internal routers cannot directly access the external neighbor's address; without rewriting, the address would be considered unreachable. After rewriting, internal routers only need to send traffic to the border router via IGP routing, and the border router handles the final external forwarding. Because I want to use IPv6 addresses to establish MP-BGP and route IPv4 over IPv6, extended next hop is enabled for IPv4. Next, create the /etc/bird/ibgp directory. Inside, create an iBGP Peer configuration file for each node: protocol bgp 'dn42_ibgp_<Node Name>' from ibgpeers{ neighbor <Corresponding Node's IPv6 ULA Address> as OWNAS; }; {collapse} {collapse-item label="Example"} /etc/bird/ibgp/hkg.conf: protocol bgp 'dn42_ibgp_HKG' from ibgpeers{ neighbor fd18:3e15:61d0::1 as OWNAS; }; {/collapse-item} {/collapse} Note: Each node needs to establish (n-1) iBGP connections, ensuring connectivity with all other machines within the AS. This is why ULA addresses are used. Using ULA addresses ensures that even if the WireGuard connection between two nodes goes down, iBGP can still establish connections via the internal routing established by OSPF. Otherwise, it could lead to the collapse of the entire internal network. Finally, add the inclusion of ibgp.conf in /etc/bird/bird.conf: include "ibgp.conf"; And run birdc configure to apply the configuration. References: BIRD 与 BGP 的新手开场 - 海上的宫殿 萌新入坑 DN42 之 —— 基于 tailscale + vxlan + OSPF 的组网 – 米露小窝 使用 Bird2 配置 WireGuard + OSPF 实现网络的高可用 | bs' realm DN42 实验网络介绍及注册教程（2022-12 更新） - Lan Tian @ Blog 如何引爆 DN42 网络（2023-05-12 更新） - Lan Tian @ Blog Bird 配置 BGP Confederation，及模拟 Confederation（2020-06-07 更新） - Lan Tian @ Blog 深入解析OSPF路径开销、优先级和计时器 - 51CTO New release 2.16 | BIRD Internet Routing Daemon 第一章·第二节 如何在 Linux 上安装最新版本的 BIRD？ | BIRD 中文文档 [DN42] 使用 OSPF ptp 搭建内网与IBGP配置 – Xe_iu's Blog | Xe_iu的杂物间 [译] dn42 多服务器环境中的 iBGP 与 IGP 配置 | liuzhen932 的小窝