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ferrix/docs/RFCs.md
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Rayhaan JaufeerallyandClaude Fable 5.1 f1d80c66df Do not choose a route whose next hop cannot be reached (RFC 4271 §9.1.2.1) 
Where routes go into the kernel, a route the kernel could not be given
is no longer taken into the table: its next hop is no neighbor on any
interface, or its prefix is a network the machine is itself on. Such a
route used to be able to win selection and then leave its prefix without
a route in the kernel, though another peer had one that worked.

It is held aside the way an RPKI-invalid route is, and by the same
means: judged on arrival against the interfaces as the kernel last
described them, looked for in the table when they change, and taken
from what is held when its next hop can be reached. The fib publishes
the interfaces for this; the next hop is resolved once for an UPDATE
and not for each of its routes.

The lab has a phase, nexthops: FRR's better route with a next hop that
is nowhere is held and BIRD's is installed, and they change places as
an address comes and goes.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
2026-10-02 20:29:31 +02:00

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# RFCs
Tracks which RFCs are implemented, partially implemented, or only represented
in the wire format layer.
**Legend**
- ✅ Implemented — functional end-to-end
- 🟡 Wire format only — parsed and serialised correctly, but not yet acted on
- ❌ Not implemented
---
## Core BGP
### RFC 4271 — A Border Gateway Protocol 4 (BGP-4)
https://datatracker.ietf.org/doc/html/rfc4271
The base protocol specification.
| Section | Description | Status |
|---------|-------------|--------|
| §4.1 | Message framing (marker, length, type) | ✅ |
| §4.2 | OPEN message | ✅ |
| §4.3 | UPDATE message (path attributes, NLRI, withdrawn routes) | ✅ |
| §4.4 | KEEPALIVE message | ✅ |
| §4.5 | NOTIFICATION message (all error codes and subcodes) | ✅ |
| §8 | FSM — passive (inbound) side: OpenSent → OpenConfirm → Established | ✅ |
| §8 | FSM — active (outbound) side: dial configured peers, exponential retry | ✅ |
| §6.2 | Bad Peer AS check against configured ASN | ✅ |
| §6.7 / RFC 4486 | Cease / Administrative Shutdown sent to every peer on SIGINT or SIGTERM | ✅ |
| §6.8 | Connection collision detection (BGP Identifier comparison, Cease / Connection Collision Resolution) | ✅ |
| §8.1.1 | Optional `CollisionDetectEstablishedState` (`collision_detect_established_state`) | ✅ |
| §6.2 | Bad BGP Identifier check (peer using our identifier, or 0.0.0.0) | ✅ |
| §9 | Decision process / best-path selection | ✅ |
| §9.1.2 | Best routes installed for forwarding (Linux kernel, over netlink), where the next hop is directly connected | ✅ |
| §9.1.2.1 | Routes with an unresolvable next hop excluded from selection | ✅ where routes are installed in the kernel: such a route is held out of the table until its next hop can be reached |
| §9.1.2.1 | Next hops resolved through other routes | ❌ (only next hops that are neighbors count as reachable) |
| §9 | Adj-RIB-In (per-peer table of received routes) | ✅ |
| §9 | Locally originated routes, advertised to all established peers | ✅ |
| §9 | Loc-RIB / Adj-RIB-Out for routes learned from peers (re-advertisement) | ❌ |
| §9.2 | Hold timer reset on any received message (not only KEEPALIVE) | ✅ |
---
## Capability and Session Extensions
### RFC 6793 — BGP Support for Four-Octet Autonomous System (AS) Number Space
https://datatracker.ietf.org/doc/html/rfc6793
| Feature | Status |
|---------|--------|
| `AS_TRANS` (23456) sentinel | ✅ |
| `FourByteAsn` capability advertisement and parsing | ✅ |
| 4-byte AS_PATH segment encoding/decoding via `ParserContext` | ✅ |
| 4-byte ASN negotiation in FSM | ✅ |
| AS4_PATH from a two-octet peer merged into AS_PATH on receipt (§4.2.3); one longer than AS_PATH ignored | ✅ |
### RFC 9774 — Deprecation of AS_SET and AS_CONFED_SET in BGP
https://datatracker.ietf.org/doc/html/rfc9774
| Feature | Status |
|---------|--------|
| Routes with an AS_SET in their path refused on import (`accept_as_sets` takes them) | ✅ |
| AS_SET never sent | ✅ |
### RFC 9072 — Extended Optional Parameters Length for BGP OPEN Message
https://datatracker.ietf.org/doc/html/rfc9072
| Feature | Status |
|---------|--------|
| Parsing extended-length OPEN (0xFF sentinel) | ✅ |
| Serialising extended-length OPEN when options exceed 255 bytes | ✅ |
### RFC 2918 — Route Refresh Capability for BGP-4
https://datatracker.ietf.org/doc/html/rfc2918
| Feature | Status |
|---------|--------|
| `RouteRefresh` capability advertisement | ✅ |
| `ROUTE-REFRESH` message type (5) framing | ✅ |
| AFI/SAFI payload parsing | ✅ |
| Acting on received ROUTE-REFRESH (re-advertising all local routes, regardless of the AFI/SAFI asked for) | ✅ |
### RFC 7313 — Enhanced Route Refresh Capability for BGP-4
https://datatracker.ietf.org/doc/html/rfc7313
| Feature | Status |
|---------|--------|
| `EnhancedRouteRefresh` capability wire format | 🟡 |
### RFC 4724 — Graceful Restart Mechanism for BGP
https://datatracker.ietf.org/doc/html/rfc4724
| Feature | Status |
|---------|--------|
| `GracefulRestart` capability wire format | 🟡 |
| Restart state and forwarding preserved across sessions | ❌ |
### RFC 9494 — Long-Lived Graceful Restart for BGP
https://datatracker.ietf.org/doc/html/rfc9494
| Feature | Status |
|---------|--------|
| `LongLivedGracefulRestart` capability wire format | 🟡 |
### RFC 8654 — Extended Message Support for BGP
https://datatracker.ietf.org/doc/html/rfc8654
| Feature | Status |
|---------|--------|
| `ExtendedMessage` capability wire format | 🟡 |
| Raising `BGP_MAX_MSG_LEN` to 65535 when negotiated | ❌ |
---
## Multiprotocol and NLRI
### RFC 2858 — Multiprotocol Extensions for BGP-4
https://datatracker.ietf.org/doc/html/rfc2858
| Feature | Status |
|---------|--------|
| `MultiProtocol` capability advertisement (IPv4 and IPv6 unicast) | ✅ |
| `MP_REACH_NLRI` path attribute (parse, serialise) | ✅ |
| `MP_UNREACH_NLRI` path attribute (parse, serialise) | ✅ |
| IPv4 and IPv6 next-hop encoding | ✅ |
### RFC 8950 — Advertising IPv4 Network Layer Reachability Information (NLRI) with an IPv6 Next Hop
https://datatracker.ietf.org/doc/html/rfc8950
| Feature | Status |
|---------|--------|
| `ExtendedNextHop` capability offered on sessions over IPv6 that carry IPv4 unicast, and used if the peer offers it | ✅ |
| IPv4 unicast routes sent and withdrawn in MP_REACH_NLRI / MP_UNREACH_NLRI with our IPv6 address as next hop | ✅ |
| IPv4 unicast routes received with an IPv6 next hop (global, or global and link-local) | ✅ |
| Such routes installed in the kernel (IPv4 route by way of an IPv6 neighbor) | ✅ |
| Other families than IPv4 unicast (VPN-IPv4, labelled) | ❌ |
| Sessions between link-local addresses (`fe80::1%eth0`), with link-local next hops | ✅ |
---
## Path Attributes and Communities
### RFC 1997 — BGP Communities Attribute
https://datatracker.ietf.org/doc/html/rfc1997
| Feature | Status |
|---------|--------|
| `COMMUNITIES` path attribute (parse, serialise) | ✅ |
| Attach to locally originated routes | ✅ |
### RFC 4360 — BGP Extended Communities Attribute
https://datatracker.ietf.org/doc/html/rfc4360
| Feature | Status |
|---------|--------|
| `EXTENDED_COMMUNITIES` path attribute (parse, serialise) | ✅ |
| AS-specific, IPv4-address-specific, opaque, route-target, route-origin subtypes | ✅ |
### RFC 8092 — BGP Large Communities Attribute
https://datatracker.ietf.org/doc/html/rfc8092
| Feature | Status |
|---------|--------|
| `LARGE_COMMUNITIES` path attribute (parse, serialise) | ✅ |
| Attach to locally originated routes | ✅ |
---
## Other Capabilities (Wire Format Only)
The following capabilities are parsed and serialised correctly but have no
functional behaviour implemented beyond that.
| RFC | Capability | Status |
|-----|-----------|--------|
| RFC 5291 | Outbound Route Filtering (ORF) | 🟡 |
| RFC 8205 | BGPsec | 🟡 |
---
## Error Handling
### RFC 9687 — BGP Send Hold Timer
https://datatracker.ietf.org/doc/html/rfc9687
| Feature | Status |
|---------|--------|
| `SendHoldTimer` error code (8) defined | ✅ |
| Send hold timer enforcement (a write that makes no progress ends the session) | ✅ |
---
## Route Security
### RFC 6811 — BGP Prefix Origin Validation
https://datatracker.ietf.org/doc/html/rfc6811
| Feature | Status |
|---------|--------|
| Validation states (valid, invalid, not found) for routes from external peers | ✅ |
| Invalid routes refused, per peer (`accept_rpki_invalid` to take them) | ✅ |
| Routes revalidated when the VRPs change, in both directions | ✅ |
| Validation of routes from internal peers and of originated routes | ❌ |
| Validity as a step of route selection (RFC 8097 communities) | ❌ |
### draft-ietf-sidrops-aspa-verification — BGP AS_PATH Verification Based on ASPA
https://datatracker.ietf.org/doc/draft-ietf-sidrops-aspa-verification/
Implemented from version 24 of the draft.
| Feature | Status |
|---------|--------|
| Upstream verification (routes from customers, peers, route servers and route server clients) | ✅ |
| Downstream verification (routes from providers) | ✅ |
| Per-peer role (`role`); paths of peers without one are not verified | ✅ |
| Invalid paths refused, per peer (`accept_aspa_invalid` to take them) | ✅ |
| Routes revalidated when the ASPAs change, in both directions | ✅ |
| Paths with an AS_SET invalid | ✅ |
| Verification on export | ❌ (learned routes are not exported yet) |
### RFC 9234 — Route Leak Prevention and Detection Using Roles in UPDATE and OPEN Messages
https://datatracker.ietf.org/doc/html/rfc9234
| Feature | Status |
|---------|--------|
| BGP Role capability sent for peers with a configured `role` | ✅ |
| Role Mismatch (OPEN Message Error, subcode 11) when the peer's role does not pair with ours, or it sends differing roles | ✅ |
| Strict mode (`require_role`) | ✅ |
| Only to Customer attribute: parse, serialise, treat-as-withdraw when malformed | ✅ |
| Ingress: marked routes from customers, route server clients and (unless marked by the peer itself) peers refused | ✅ |
| Ingress: routes from providers, peers and route servers marked | ✅ |
| Egress: originated routes to customers, peers and route server clients marked | ✅ |
| Egress: marked routes not sent to providers, peers or route servers | ❌ (learned routes are not exported yet) |
### RFC 8210 — The RPKI to Router Protocol, Version 1 (RFC 6810, version 0; draft-ietf-sidrops-8210bis, version 2)
https://datatracker.ietf.org/doc/html/rfc8210
Version 2 is implemented from version 23 of the draft.
| Feature | Status |
|---------|--------|
| Reset and serial queries, notifies, cache reset, incremental updates | ✅ |
| Refresh, retry and expire intervals; data dropped when it expires | ✅ |
| Version 2, with fallback to 1 and 0; several caches with failover | ✅ |
| ASPA PDU (version 2) | ✅ |
| Error Reports sent to the cache | ✅ |
| Version 2's ordering of PDUs enforced on what a cache sends | ❌ (any order is taken) |
| Transport over plain TCP | ✅ |
| Transport over SSH, TLS, TCP-MD5 or TCP-AO | ❌ |
| Router keys (BGPsec) | 🟡 read and ignored |
### RFC 7911 — Advertisement of Multiple Paths in BGP (ADD-PATH)
https://datatracker.ietf.org/doc/html/rfc7911
| Feature | Status |
|---------|--------|
| Capability negotiation per family and direction | ✅ |
| Receiving several routes for a prefix | ✅ |
| Sending several routes for a prefix | ❌ (path identifiers are sent; one route each) |
### RFC 4271 §9.1.2 / RFC 4486 / operational practice — import policy
| Feature | Status |
|---------|--------|
| Own AS in path refused (loop detection) | ✅ |
| Bogon prefixes and AS numbers, prefix length bounds, first-AS check | ✅ |
| Per-peer prefix and origin AS allow-lists | ✅ |
| Maximum prefixes with Cease / Maximum Number of Prefixes Reached and hold-down | ✅ |
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