[BUG] bgp.local_as not working with VLAN

[ssasso]

Describe the bug

When vlans are in use together with "vlan level" bgp.local_as, local config is good, but peer config still have the "previous" AS number.

To Reproduce

Topology:

provider: clab
defaults.device: frr
module: [ bgp ]

nodes:
  r1:
    module: [ vlan, bgp ]
    bgp.as: 65000
    vlans:
      red:
        bgp.local_as: 65001
  r2:
    bgp.as: 65002
  r3:
    bgp.as: 65003

vlans:
  red:
  green:

links:
- r1:
    vlan.access: red
  r2:
- r1:
    vlan.access: green
  r3:

netlab inspect --node r2 | yq .bgp.neighbors[0]:

{
  "ifindex": 1,
  "name": "r1",
  "as": 65000,
  "type": "ebgp",
  "ipv4": "172.16.0.1",
  "activate": {
    "ipv4": true
  }
}

generated R2 config:

router bgp 65002
 neighbor 172.16.0.1 remote-as 65000
 neighbor 172.16.0.1 description r1

generated R1 config:

router bgp 65000
 neighbor 172.16.0.2 remote-as 65002
 neighbor 172.16.0.2 local-as 65001 no-prepend replace-as
 neighbor 172.16.0.2 description r2

Expected behavior

R2 config:

router bgp 65002
 neighbor 172.16.0.1 remote-as 65001
 neighbor 172.16.0.1 description r1

Version

dev

[ipspace]

Did you really have to??? 😢🤦‍♂️ And I hoped I will never have to touch the VLAN code again 🤢

On a more serious note, thanks a million for uncovering this one. From my guesspoint perspective, it looks like the interface neighbor list is built before the (neighbor) SVI data is augmented with the node VLAN data.

No idea how long it will take me to fix it.

[ssasso]

before the SVI data is augmented with the node VLAN data

But - at least in theory - bgp transformation should happen after vlan, if I understand this correctly:

netlab/netsim/modules/bgp.yml

Line 16 in a8f60ea

transform_after: [ vlan ]

[jbemmel]

before the SVI data is augmented with the node VLAN data

But - at least in theory - bgp transformation should happen after vlan, if I understand this correctly:

netlab/netsim/modules/bgp.yml

Line 16 in a8f60ea

transform_after: [ vlan ]

There's more to it than that. For example:

• netlab/netsim/augment/links.py

  Line 329 in a8f60ea

  def add_node_interface(node: Box, ifdata: Box, defaults: Box) -> Box:

  creates node interfaces, processing attributes like mtu but not bgp.local_as associated with an access VLAN on that interface

• netlab/netsim/modules/bgp.py

  Line 738 in a8f60ea

  def collect_bgp_attr(attr: Box, obj: Box, o_name: typing.Optional[str] = None) -> None:

  processes vlan data structures to look at bgp.local_as, but only to warn about it when used on intra-AS links

The order of processing applies per hook. From what I can tell, it's not so much about the order, but about the bgp.local_as from the node VLAN data not being added to the neighbor (i.e. missing processing step)

[ipspace]

But - at least in theory - bgp transformation should happen after vlan, if I understand this correctly:

That is correct, but the BGP transformation uses neighbors interface data that was collected during the main link transformation, and that data does not include the node VLAN data because that's added in the post_link VLAN hook when the SVI interfaces are created.

I will probably add some extra code to add node VLAN data to neighbor data in the link transformation phase.