Nexus5548 BGP soft-reconfiguration inbound

[m.o.andersson_2]

Hi,

I have a small problem when using Nexus5548 version 5.2(1)N1(2a) with BGP and

soft-reconfiguration inbound

The BGP config looks exactly like other Nexus implementations with BGP but with N5K im not able to see

show ip bgp neighbors x.x.x.x received-routes

I get the error message saying:

% Inbound soft reconfiguration for IPv4 Unicast not enabled on x.x.x.x

The BGP-config looks like this:

router bgp [ASN]
  router-id 1.2.3.4
  neighbor x.x.x.x remote-as [eBGP_ASN]
    address-family ipv4 unicast
      route-map BGP_prim in
      soft-reconfiguration inbound

The neighbor looks like it supports this feature:

  Neighbor capabilities:
  Dynamic capability: advertised (mp, refresh, gr)
  Dynamic capability (old): advertised
  Route refresh capability (new): advertised received
  Route refresh capability (old): advertised received
  4-Byte AS capability: advertised received
  Address family IPv4 Unicast: advertised received
  Graceful Restart capability: advertised

Any idea where im going wrong or is it not possible to do this in N5K?

Cheers! // Mattias

[Peter Paluch]

Mattias,

I may be answering a slightly different question but here goes: Are you sure you need the

soft-reconfiguration inbound?

Are you perhaps confusing this feature with route refresh, a different feature?

It appears that most people do not differentiate between these two features. They provide the same functionality but use vastly different means of accomplishing them.

The

soft-reconfig inbound 

is an ancient workaround about BGP's former inability to ask a neighbor to repeatedly resend a set of routes. Cisco devices have traditionally solved this problem by storing a separate, unfiltered copy of all routes received from a particular neighbor configured with the

neighbor soft-reconfig inbound

command. Every change on the inbound policy would then simply re-filter the routes from the unfiltered database maintained on a per-neighbor basis. An obvious disadvantage of this approach is the amount of wasted memory to keep unfiltered BGP databases for each neighbor for which you have configured the

soft-reconfig inbound

In RFC 2918 which is 15 years old by now, a new BGP message was standardized: the Route Refresh message. Using this message, a BGP router can ask its neighbor at any time to resend a particular family of routes (IPv4 routes, IPv6 routes, etc.). No storing of unfiltered databases is necessary anymore. In addition, this Route Refresh is negotiated and used automatically as soon as both routers support it.

Now, your Nexus tells you right away:

  Route refresh capability (new): advertised received
  Route refresh capability (old): advertised received

It is telling you that both your Nexus (advertised) and its neighbor (received) support the Route Refresh feature, and as a result, they will be using it automatically, without you configuring anything in particular.

If you configured

soft-reconfig inbound

for a neighbor, you would be losing the advantages of Route Refresh, as you would be forcing your router to store unfiltered routes from the neighbor even though both routers support the Route Refresh and storing the unfiltered database is entirely useless.

It is possible that NX-OS tries to do things the smart way, and when it finds out that both peers support Route Refresh, it uses it in place of

soft-reconfig inbound

even if you have it configured. I am not fluent in NX-OS so I cannot comment on that with certainty but it is a possibility.

In any case, to show the routes received from a neighbor, you should use just

show ip bgp neighbor x.x.x.x received routes (not received-routes).

Would you mind trying this out? If this works for you then I suggest that you remove the

soft-reconfig inbound

from your configuration. It seems to be useless in your (and in most people's) case.

Best regards,
Peter

[m.o.andersson_2]

Thanks for the enlightenment! Ive always used this feature to see recived routes, now i know better. Still, im afraid it doesnt work. I tride with and without the

soft-configuration inbound

command. But i still get an error:

sh ip bgp neighbors x.x.x.x routes received
% Inbound soft reconfiguration for IPv4 Unicast not enabled on x.x.x.x

Strange... Seems more like the feature is not there or if there is a bug. I run this config on other Nexus routers, N7K for example. It works like a charm.. 

[Peter Paluch · Accepted solution]

Mattias,

Okay... on IOS-based devices, there are two commands:

show ip bgp neighbor x.x.x.x received-routes ! 

Shows the Soft Reconfig Inbound routes

show ip bgp neighbor x.x.x.x routes !

Shows routes received from a neighbor

Are there any similar commands on NX-OS?

Best regards,
Peter

[m.o.andersson_2]

Oh, now when i type:

sh ip bgp neighbors x.x.x.x routes

I get the recieved routes. But if i add "received" after the "routes" statement i get the error. Well it worked. Thanks alot for the help. I will now remove all soft-reconfig statements. :)

[Martial Nkounkou]

The issue is with your configuration. You must add the keyword always.

router bgp [ASN]
  router-id 1.2.3.4
  neighbor x.x.x.x remote-as [eBGP_ASN]
    address-family ipv4 unicast
      route-map BGP_prim in
      soft-reconfiguration inbound always.
 

[AliMohammed]

Well done peter was helpful