BGP: Expose deeper neighbor information

This issue tracks a request to expand the information exposed about a given BGP neighbor.

For example, it's useful to expose some L3/L4 information like the local and remote IP addresses and TCP port numbers so that a constrained packet capture can be done elsewhere in the network. Other useful info would be things like MSS, ttl-security of the session / whether or not the neighbor is multi-hop, what the keepalive/holdtime timers are (both configured and negotiated), per-message counters, negotiated capabilities (including address-families), configured inbound/outbound policy, etc.

A good example of what info we would want is the info that can be collected from FRR:

debbie# show ip bgp neighbors 
BGP neighbor is 174.27.32.105, remote AS 65000, local AS 65001, external link
  Local Role: undefined
  Remote Role: undefined
  BGP version 4, remote router ID 0.0.0.0, local router ID 172.30.0.5
  BGP state = Active (passive)
  Last read 17:52:09, Last write never
  Hold time is 180 seconds, keepalive interval is 60 seconds
  Configured hold time is 180 seconds, keepalive interval is 60 seconds
  Configured tcp-mss is 1000, synced tcp-mss is 0
  Configured conditional advertisements interval is 60 seconds
  Graceful restart information:
    Local GR Mode: Helper*
    Remote GR Mode: NotApplicable
    R bit: False
    N bit: False
    Timers:
      Configured Restart Time(sec): 120
      Received Restart Time(sec): 0
      Configured LLGR Stale Path Time(sec): 0
  Message statistics:
    Inq depth is 0
    Outq depth is 0
                         Sent       Rcvd
    Opens:                  0          0
    Notifications:          0          0
    Updates:                0          0
    Keepalives:             0          0
    Route Refresh:          0          0
    Capability:             0          0
    Total:                  0          0
  Minimum time between advertisement runs is 0 seconds

 For address family: IPv4 Unicast
  Not part of any update group
  Community attribute sent to this neighbor(all)
  Inbound updates discarded due to missing policy
  Outbound updates discarded due to missing policy
  0 accepted prefixes

  Connections established 0; dropped 0
  Last reset 17:52:09,  No path to specified Neighbor (n/a)
  External BGP neighbor may be up to 1 hops away.
BGP Connect Retry Timer in Seconds: 120
Read thread: off  Write thread: off  FD used: -1

Not all of the info above is relevant to us (e.g. BGP Roles, BGP version, conditional advertisement), but we should strive to expose similar levels of operational info.

Note that some of this is available already through the mgd API. For example, you can see configured/negotiated hold and keepalive timers.

$ mgadm bgp status neigh $ASN
Peer Address  Peer ASN     State        State Duration          Hold   Keepalive
172.20.15.51  Some(64601)  Established  1day 17h 56m 50s 584ms  6s/6s  2s/2s

and as-configured info is also available through the API.

$ mgadm bgp config neigh list $ASN
[
    Neighbor {
        allow_export: Allow(
            [
                V4(
                    Prefix4 {
                        length: 24,
                        value: 172.20.26.0,
                    },
                ),
            ],
        ),
        allow_import: NoFiltering,
        asn: 65002,
        communities: [],
        connect_retry: 3,
        delay_open: 3,
        enforce_first_as: false,
        group: "qsfp18",
        hold_time: 6,
        host: "172.20.15.51:179",
        idle_hold_time: 3,
        keepalive: 2,
        local_pref: None,
        md5_auth_key: None,
        min_ttl: None,
        multi_exit_discriminator: None,
        name: "172.20.15.51",
        passive: false,
        remote_asn: None,
        resolution: 100,
        vlan_id: None,
    },
]

oxidecomputer / maghemite

BGP: Expose deeper neighbor information #387