[RFE] EVPN-Driver: Get the AS Number from config

[Justin Lamp]

# Problem Statement

We run an eBGP Setup in our fabric which results in different AS Numbers per Gateway. This makes the current EVPN implementation impractical as one would need to update the AS on the Router Ports on every failover.

# Proposed Solution

I propose that the keyword "dynamic" as the AS external_id would get the AS out of the already defined config option.

```
ovn-nbctl set Logical_Switch_Port $LS 'external_ids:"neutron_bgpvpn:as"="dynamic"'
```

```
int(CONF.bgp_AS) if asn == "dynamic" else int(asn))
```

[Justin Lamp (modzilla)]

How should this be implemented? Do you prefer that the "neutron_bgpvpn:as" should be present in order to use the AS configured in the agent.conf or would it be better to check whether it is absent?

[Maximilian Sesterhenn (msnatepg)]

Hello,

just for reference here:
We had exactly the same issue while implementing L2 EVPN.

We've published a new Change for the neutron-bgpvpn OVN service driver [1] that removes this AS field in the external_ids entirely while adding additional fields that BGPVPN offers.

If the same AS has to be used on all nodes this can be achieved by configuring the same AS is all agents config files.

At the same time we published another Change [2] for ovn-bgp-agent that implements these new fields for L2 EVPN. The old SB EVPN driver is still unchanged.

I talked to Luis and the plan is to merge this with little changes soon.

[1] https://review.opendev.org/c/openstack/networking-bgpvpn/+/883060
[2] https://review.opendev.org/c/openstack/ovn-bgp-agent/+/886090

[Justin Lamp (modzilla)]

Hi,

that's great news! Will wait for your MR then.

Thanks!

Best regards,
Justin Lamp