Routing protocols

Status: draft

Notes on OSPFv2 / OSPFv3 / BGP-4 / RIPv1 and v2 / RIPng / EIGRP. Definitions are in crates/wpg-protocols/src/routing.rs, samples in templates/protocols/routing/. OSPFv2 Opaque LSAs / Segment Routing and the BGP multiprotocol NLRI (IPv6, VPN, EVPN) are described on the OSPF Opaque / SR, BGP MP / VPN / EVPN page.

How they are reached, and samples

id	Protocol	Layer below	Samples
`ospfv2` + body	OSPFv2 (RFC 2328)	IPv4 protocol 89	`ospfv2-hello` / `-dbd` / `-lsr` / `-lsu-*` / `-lsack` (opaque LSAs: `ospfv2-lsu-te-lsa`, `-ri-sr`, `-ext-prefix-sr`, `-ext-link-sr`)
`ospfv3` + body	OSPFv3 (RFC 5340)	IPv6 next header 89	`ospfv3-hello` / `-dbd` / `-lsr` / `-lsu-*` / `-lsack`
`bgp` + body	BGP-4	TCP 179 (destination, else source)	`bgp-open` / `-update` / `-keepalive` / `-notification` / `-route-refresh`, `bgp-update-mp-ipv6` / `-vpnv4` / `-evpn`
`rip`	RIPv1 / v2	UDP 520	`ripv1-request`, `ripv2-response`
`ripng`	RIPng	UDP 521	`ripng-response`
`eigrp`	EIGRP (basic TLVs)	IP protocol 88 (IPv4 / IPv6)	`eigrp-hello`, `eigrp-update`

Stacking the layers

OSPF and BGP are two layers, the common header and the body (an LSU adds an LSA header and an LSA body).

ipv4 / ospfv2 / ospfv2_hello
ipv4 / ospfv2 / ospfv2_lsu / ospfv2_lsa / ospfv2_router_lsa
ipv4 / ospfv2 / ospfv2_lsu / ospfv2_opaque_lsa / ospfv2_ri_lsa   # LS type 9 / 10 / 11
ipv6 / ospfv3 / ospfv3_lsu / ospfv3_lsa / ospfv3_intra_area_prefix_lsa
ipv4 / tcp / bgp / bgp_update
ipv4 / tcp / bgp                 # a KEEPALIVE is the header alone (type 4 is the default)

Auto fields

OSPF header type, packet_length and checksum. The OSPFv3 checksum includes the IPv6 pseudo header and is exact.
LSA header ls_type, length and ls_checksum (Fletcher, LS age excluded; exact for any age).
Router-LSA num_links.
BGP header length and type; OPEN opt_params_length; UPDATE withdrawn_routes_length and total_path_attribute_length; the Extended Length flag of path attributes longer than 255 octets.
EIGRP checksum.

Fields you set by hand

num_lsas of ospfv2_lsu / ospfv3_lsu (normally 1: an LSU carries one typed LSA).
ls_checksum of the LSA headers listed inside DBD / LSAck.

Limits and approximations

OSPFv2 authentication: the checksum leaves out the 64-bit authentication field, so it is exact for null and simple-password authentication. With cryptographic authentication (AuType 2) set the checksum to 0 by hand (in the builder, turn on “Allow malformed packets” to override it). The cryptographic-auth trailer after the packet is not modelled.
One typed LSA per LSU: there is no repeated-layer construct, so no further LSA can follow a typed LSA body.
LS types sharing a body: OSPFv2 types 3 / 4 and 5 / 7, and OSPFv3 0x4005 / 0x2007, have the same body layout, so Auto announces the first type. For the other one set ls_type by hand (a next-protocol mismatch warning results, but the packet can be sent).
OSPFv2 TOS entries (router-link num_tos > 0, summary / external TOS metrics) and the OSPFv3 prefix lists are not typed; they stay opaque prefixes / address_prefix octets.
BGP routes (NLRI / withdrawn routes) are lists of {length, prefix} (length in bits, ceil(length / 8) prefix octets). A hex string is still accepted as verbatim octets.
BGP path attributes are a TLV with a 16-bit type (flags << 8 | type code); the length is 8 bits, or 16 bits with the Extended Length flag (0x10), which is set automatically above 255 octets and kept when given in an explicit type. AS_PATH / AGGREGATOR use 4-octet AS numbers (RFC 6793). Extended optional parameters (RFC 9072) are not supported.
Only the first BGP message in a segment is decoded.
EIGRP route TLVs end in a variable-length destination (ceil(prefix_length / 8) octets), kept as destination octets running to the end of the TLV value; a multi-destination TLV stays in that one field.

Generated reference

Field reference of the protocols on this page (generated from the definitions):

ospfv2 · ospfv2_lsu · ospfv3 · ospfv3_lsu · bgp · rip · ripng · eigrp

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