bgpv1: Add support for eBGP-multihop in BGP control plane

[rastislavs]

Extends the CiliumBGPNeighbor configuration in the CiliumBGPPeeringPolicy CRD with a new configuration option: EBGPMultihopTTL. This can be used to enable multihop feature for eBGP peers, with explicit TTL hop limit count.

Example Configuration:

apiVersion: "cilium.io/v2alpha1"
kind: CiliumBGPPeeringPolicy
metadata:
  name: tor
spec:
  virtualRouters:
  - localASN: 65001
    exportPodCIDR: true
    neighbors:
    - peerAddress: "172.0.0.1/32"
      peerASN: 65000
      eBGPMultihopTTL: 10   # >=1 means enabled, 0 means disabled, default=0.

Example state dump of peers after configuring:

# cilium bgp peers -o json
[
  {
    "applied-hold-time-seconds": 90,
    "applied-keep-alive-time-seconds": 30,
    "configured-hold-time-seconds": 90,
    "configured-keep-alive-time-seconds": 30,
    "connect-retry-time-seconds": 60,
    "ebgp-multihop-ttl": 10,
    "families": [
      {
        "advertised": 1,
        "afi": "ipv4",
        "received": 1,
        "safi": "unicast"
      },
      {
        "afi": "ipv6",
        "safi": "unicast"
      }
    ],
    "local-asn": 65001,
    "peer-address": "172.0.0.1",
    "peer-asn": 65000,
    "session-state": "established",
    "uptime-nanoseconds": 53443700101
  }
]

Example dump of a keepalive packet:

Fixes: #21753

Add support for eBGP-multihop configuration for CiliumBGPNeighbor in CiliumBGPPeeringPolicy CRD

[dylandreimerink]

We should also add this feature to the docs: https://docs.cilium.io/en/stable/network/bgp-control-plane/ which are at
Documentation/network/bgp-control-plane.rst

[YutaroHayakawa]

LGTM 👍

[rolinh]

Vendor changes lgtm.

[rastislavs]

Unfortunately, after rebasing with the recent bgpv1 unit tests changes, a unit test started triggering a timing issue that I had to fix in upstream: osrg/gobgp#2663

It seems that until the next GoBGP release we would need to stay on the version v3.15.1-0.20230605074248-03982e597eacz (one commit after the v3.15.0). Is this any problem in general in regards with Cilium dependencies @rolinh ? I see that there are multiple other dependencies like that in go.mod.

[rolinh]

It seems that until the next GoBGP release we would need to stay on the version v3.15.1-0.20230605074248-03982e597eacz (one commit after the v3.15.0). Is this any problem in general in regards with Cilium dependencies @rolinh ?

No, it isn't a problem 🙂

[rastislavs]

/test

[rastislavs]

Cilium L4LB XDP (ci-l4lb) test failing: hitting complexity issue (#25892). Rebasing to pull the fix.

[rastislavs]

/test

[nathanjsweet]

LGTM for API.