[rbak-nsp] Re: Subcriber route and metric

[Blake Willis]

On 18.01.2013 10:12, redback-nsp-request at puck.nether.net wrote:

> I would prefer to have subscriber configuration in radius for easy 
> management.
> I've tried to add FrameRoute to botch cpe-login with metric like this 
> :
>
> cpe1 at redback Framed-Route += 172.20.1.0/24 0.0.0.0 5 # master
> cpe2 at redback Framed-Route += 172.20.1.0/24 0.0.0.0 10 # master
>
> but this not work as expected. The metric are well seen in show ip 
> route, but it look the last cpe
> connected win, like there is only possibilite for one subsciber route 
> entry for a given route

Bonjour Raphael,

Welcome to the joys of Redback subscriber routing...  I'm not sure what 
SEOS version you're running or whether their architecture has changed in 
recent releases, but in the 6.1 trains I'm most familiar with, 
subscriber routes have the particularity of not being able to 
load-balance or handle redundancy properly.  The behavior is as you 
describe.  When trying to load-balance across multiple subscriber routes 
with the same metric, the box will even go so far as to install all 
three next-hops in the FIB and blackhole traffic to all but the most 
recent connection.  I observed the same behavior running RIP with the 
CPE learning three identical routes, but I believe this may have been 
fixed in recent releases.

We have used a couple of workarounds, none of which are particularly 
nice but they do get the job done:

  - cut your "primary" /24 route into two /25s so that the shortest 
prefixes will be preferred and you don't have the same set of routes 
pointing at each subscriber (increases framed-route count by 50% 
though)-:

  - create "primary" and "backup" contexts, and make sure that two 
logins from the same site never show up in the same context.

As a side note, you'll also find that the framed-routes are really 
bound to the subscriber circuit & not the IP next-hop in the 
framed-route.  You can put just about anything as a next-hop in radius 
and the traffic will still go down the subscriber circuit.

Hope that helps.

Best regards,
---
   Blake Willis
   Network Architecture Consultant & Co-founder
   L33 Networks