[j-nsp] Advertising inactive routes to iBGP neighbors

[James]

Hi Crist,

Consider a server connected to two leaf switches with edge routed EVPN
ESI multihoming. The static route is present on both leaf switches
which under normal circumstances causes ingress traffic to be ECMP'ed
towards both switches.

If the link between leaf 1 and the server goes down, the EVPN route is
removed but the static route remains active since the next-hop is
still technically reachable over VXLAN. If only the static route were
to be redistributed, some ingress traffic would take a suboptimal path
from the spine to leaf 1, which then encapsulates it with VXLAN and
sends it back to the spine to be delivered to leaf 2, which then needs
to decapsulate it to deliver to the server.

Advertising the static route at a lower localpref to the EVPN route
would have the following consequences:
- If none of the leaf switches have learned the EVPN route yet, the
static route acts like a fallback to allow ingress routing to still
work.
- If the link between one leaf and the server fails, ingress traffic
no longer gets ECMP'ed to that leaf due to the higher localpref on the
route from the other leaf/leaves.

If there's an easier solution that I'm missing, please let me know.

Thanks,
James


On Mon, Apr 18, 2022 at 12:11 AM Crist Clark <cjc+j-nsp at pumpky.net> wrote:
>
> I don't quite understand. Why don't you just export the static into your routing protocol? How is the static route a "fallback" if it is really the active route?
>
> On Sun, Apr 17, 2022 at 8:57 AM James via juniper-nsp <juniper-nsp at puck.nether.net> wrote:
>>
>>
>>
>>
>> ---------- Forwarded message ----------
>> From: James <james at nexril.net>
>> To: juniper-nsp at puck.nether.net
>> Cc:
>> Bcc:
>> Date: Sun, 17 Apr 2022 10:49:44 -0500
>> Subject: Advertising inactive routes to iBGP neighbors
>> Hi all,
>>
>> I have two routes in inet.0, neither of which come from BGP:
>>
>> 10.200.7.2/32      *[Static/5] 00:14:40
>>                     >  to 10.200.7.2 via irb.102
>>                     [EVPN/7] 00:08:25
>>                     >  via irb.102
>>
>> I want to advertise the 'EVPN/7' route, either alongside or completely in place
>> of the 'Static/5' route. The particular use case here is EVPN-VXLAN virtual
>> machine traffic optimization, where I want to advertise the EVPN route with a
>> higher localpref to steer traffic towards one or more particular leaf switches
>> while still advertising the static route as a fallback in case the EVPN route
>> is not there. Normally this works because the attached prefixes are longer than
>> a /32, but I just can't seem to figure out how to make this work with /32
>> statically routed prefixes.
>>
>> I've already tried several methods including rib-groups to bring the route into
>> another table (no support for rib-groups with EVPN routes), bgp add-path
>> (doesn't advertise the second path), and playing with route preferences
>> (static route needs to be the active route for forwarding purposes), but none
>> of those have been successful.
>>
>> Any other suggestions on how I could achieve this?
>>
>> Thanks,
>> James
>>
>>
>>
>> ---------- Forwarded message ----------
>> From: James via juniper-nsp <juniper-nsp at puck.nether.net>
>> To: juniper-nsp at puck.nether.net
>> Cc:
>> Bcc:
>> Date: Sun, 17 Apr 2022 10:49:44 -0500
>> Subject: [j-nsp] Advertising inactive routes to iBGP neighbors
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