Nexus5548 BGP soft-reconfiguration inbound

Question

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

Answer 1

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