LDP / RSVP-TE / BFD (P2)

Status: draft

Notes on LDP (RFC 5036), RSVP-TE (RFC 2205 / RFC 3209) and BFD (RFC 5880 / 5881 / 5883, Micro-BFD RFC 7130) (M7). The definitions live in crates/wpg-protocols/src/{ldp,rsvp,bfd}.rs, the samples in templates/protocols/mpls/ and templates/protocols/oam/.

Stacks and samples

ethernet2 / ipv4 / udp / ldp       # UDP 646: Hello (basic discovery to 224.0.0.2, extended to a unicast address)
ethernet2 / ipv4 / tcp / ldp       # TCP 646: the session (Initialization onwards)
ethernet2 / ipv4 / rsvp            # IPv4 protocol 46 (Auto)
ethernet2 / ipv6 / rsvp            # IPv6 next header 46 (Auto)
ethernet2 / ipv4 / udp / bfd       # UDP 3784 (single hop), 4784 (multihop), 6784 (Micro-BFD)

LDP over IPv6 (RFC 7552) is ipv6 / udp|tcp / ldp. UDP / TCP destination ports are not Auto: set 646, 3784, … (decoding also recognises the source port). The BFD echo port 3785 is not decoded: its contents only mean something to the sender.

LDP: one layer is one PDU

The ldp layer is the PDU header (version, pdu_length, lsr_id, label_space) and every message of the PDU (messages). Messages end at the PDU length, so a further PDU in the same TCP segment becomes the next layer (raw).

Messages and TLVs are items of the same shape: a 16-bit type (the U bit, and for TLVs the F bit, are its top bits), a 16-bit length of the value only, and the value. Every message starts with message_id, followed by tlvs.

- protocol: ldp
  fields:
    lsr_id: 192.0.2.1
    messages:
      - label_mapping:
          message_id: 11
          tlvs:
            - fec:
                elements: [{ prefix_length: 24, prefix: "c6 33 64" }]
            - generic_label: { label: 299776 }
      - label_withdraw:
          message_id: 12
          tlvs:
            - fec_wildcard

The FEC TLV is decoded as fec_wildcard or fec from the first value octet (the element type), the Address List as IPv4 or IPv6 from the first two (the address family). Other types (ATM / Frame Relay labels and session parameters, vendor TLVs, …) are kept as { type: N, data: "..." }.

RSVP-TE: objects are “length, then type”

The rsvp layer is the common header (version, flags, msg_type, checksum, send_ttl, length) and every object of the message (objects). An object is a 16-bit length (counting the 4-octet header) followed by the Class-Num and C-Type, read together as one 16-bit type (class_num << 8 | c_type; wpg-core TlvDef::len_first). Item names combine the class and the C-Type.

EXPLICIT_ROUTE subobjects are ipv4_prefix, ipv6_prefix, unnumbered_interface and as_number; the names ending in _loose have the L bit (loose hop). RECORD_ROUTE subobjects are ipv4_address, ipv6_address, label and unnumbered_interface (each with flags). ADSPEC, POLICY_DATA, INTEGRITY and other objects keep their value octets.

The token bucket of SENDER_TSPEC / FLOWSPEC (token_bucket_rate, token_bucket_size, peak_data_rate) is given as IEEE 754 single-precision bit patterns in 32-bit integers (1,000,000 octets/s = 0x49742400, infinity = 0x7f800000). The default is 125,000 octets/s (1 Mbit/s).

Path, PathTear and ResvConf are normally sent with the IP Router Alert option (ipv4 options: [router_alert: 0]).

BFD

The bfd layer is the mandatory section and the optional authentication section (authentication). The flags are the 1-bit fields p, f, c, a, d and m. Authentication types are simple password (simple_password: key_id, password), keyed_md5 / meticulous_keyed_md5 (key_id, sequence_number, a 16-octet digest) and keyed_sha1 / meticulous_keyed_sha1 (a 20-octet hash).

- protocol: bfd
  fields:
    state: up
    my_discriminator: 0x101
    your_discriminator: 0x201
    desired_min_tx_interval: 300000 # microseconds
    required_min_rx_interval: 300000
    authentication:
      - simple_password: { key_id: 1, password: '"secret"' }

Auto fields

Limitations

• No state: no LDP session setup, RSVP refresh, or BFD state machine and timers. Values are sent as given; use generators to vary them.
• BFD MD5 digests / SHA1 hashes and the RSVP INTEGRITY object are Manual (nothing is computed from a key).
• One LDP layer is one PDU; further PDUs in the same segment decode as raw.
• RSVP does not type the GMPLS objects (RFC 3473), ADSPEC or POLICY_DATA; RSVP over UDP (RFC 2205 appendix C) is out of scope.
• Only the first IntServ parameter (the token bucket) is typed; later ones (the guaranteed service rate / slack term, …) are parameters octets.

Generated reference

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

ipv4 · ldp · rsvp · bfd · raw