[c-nsp] Loop/Unreachable problem with C6500/SUP720

Wed Aug 8 12:29:12 EDT 2012

Are this routes all running in the ospf and bgp at the same time? If yes, it is a normal behaviour.

Thanks and regards,
Xu Hu

On 8 Aug, 2012, at 22:27, Sebastian Wiesinger <cisco-nsp at ml.karotte.org> wrote:

> Hello,
> 
> I'm having a strange problem with a Cisco 6500/SUP720 running
> 12.2(33)SXJ3.
> 
> Currently we're testing this router in the lab. We have one OSPF
> connection to the outside and iBGP enabled.
> 
> As soon as I enable the iBGP i get really strange effects:
> 
> I have 10.1.66.0/25 connected to a SVI (Vlan412) and all IPs are
> terminated on one server for testing.
> 
> Now when I ping some IPs I get a normal answer:
> 
> 
> $ ping 10.1.66.51
> PING 10.1.66.51 (10.1.66.51) 56(84) bytes of data.
> 64 bytes from 10.1.66.51: icmp_req=1 ttl=60 time=3.88 ms
> 64 bytes from 10.1.66.51: icmp_req=2 ttl=60 time=3.91 ms
> 
> And now the problem:
> 
> $ ping 10.1.66.84
> PING 10.1.66.84 (10.1.66.84) 56(84) bytes of data.
> From 10.2.14.9 icmp_seq=1 Time to live exceeded
> From 10.2.14.9 icmp_seq=2 Time to live exceeded
> From 10.2.14.9 icmp_seq=3 Time to live exceeded
> 
> A traceroute shows the packet is looping, the lab router is sending it
> back to it's OSPF peer (instead of sending it out through Vl412) who
> sends it straight back:
> 
> 5  10.2.14.10  4.592 ms  4.561 ms  4.575 ms
> 6  10.2.14.9  4.996 ms  4.162 ms  4.240 ms
> 7  10.2.14.10  4.204 ms  4.135 ms  4.156 ms
> 8  10.2.14.9  4.273 ms  4.193 ms  4.106 ms
> 9  10.2.14.10  4.015 ms  4.237 ms  4.156 ms
> ...
> 
> Issuing various commands I can see no difference between the two IPs
> on the router:
> 
> lab-rtr1#show ip route 10.1.66.51                          
> Routing entry for 10.1.66.0/25
>  Known via "connected", distance 0, metric 0 (connected, via interface)
>  Routing Descriptor Blocks:
>  * directly connected, via Vlan412
>      Route metric is 0, traffic share count is 1
> 
> lab-rtr1#show ip route 10.1.66.84
> Routing entry for 10.1.66.0/25
>  Known via "connected", distance 0, metric 0 (connected, via interface)
>  Routing Descriptor Blocks:
>  * directly connected, via Vlan412
>      Route metric is 0, traffic share count is 1
> 
> 
> CEF entries:
> 
> 
> lab-rtr1#show ip cef adjacency Vlan412 10.1.66.51 internal 
> IPv4 CEF is enabled for distributed and running
> VRF base:
> 64739 prefixes (64737/2 fwd/non-fwd)
> Default network 0.0.0.0/0
> Table id 0
> Database epoch:        7 (64739 entries at this epoch)
> 
> 10.1.66.51/32, epoch 7, flags attached, refcount 4, per-destination sharing
>  sources: Adj 
>  feature space:
>   NetFlow: Origin AS 0, Peer AS 0, Mask Bits 25
>  subblocks:
>   Adj source: IP adj out of Vlan412, addr 10.1.66.51 5136EEC0
>    Dependent covered prefix type adjfib cover 10.1.66.0/25
>  ifnums:
>   Vlan412(180): 10.1.66.51
>  path 5110F968, path list 5110C090, share 1/1, type adjacency prefix, for IPv4
>  attached to Vlan412, adjacency IP adj out of Vlan412, addr 10.1.66.51 5136EEC0
>  output chain: IP adj out of Vlan412, addr 10.1.66.51 5136EEC0
> 
> lab-rtr1#show ip cef adjacency Vlan412 10.1.66.84 internal 
> IPv4 CEF is enabled for distributed and running
> VRF base:
> 64739 prefixes (64737/2 fwd/non-fwd)
> Default network 0.0.0.0/0
> Table id 0
> Database epoch:        7 (64739 entries at this epoch)
> 
> 10.1.66.84/32, epoch 7, flags attached, refcount 4, per-destination sharing
>  sources: Adj 
>  feature space:
>   NetFlow: Origin AS 0, Peer AS 0, Mask Bits 25
>  subblocks:
>   Adj source: IP adj out of Vlan412, addr 10.1.66.84 5136A6C0
>    Dependent covered prefix type adjfib cover 10.1.66.0/25
>  ifnums:
>   Vlan412(180): 10.1.66.84
>  path 51110C70, path list 5110D2F8, share 1/1, type adjacency prefix, for IPv4
>  attached to Vlan412, adjacency IP adj out of Vlan412, addr 10.1.66.84 5136A6C0
>  output chain: IP adj out of Vlan412, addr 10.1.66.84 5136A6C0
> 
> This is totally random. When I shut/no shut the SVI the problem goes
> away and comes back soon after but on different IPs.
> 
> Clearing the CEF table has the same effect.
> 
> When I shut down BGP the problem seems to go away.
> 
> Also BGP sessions are flapping from time to time without apparent
> reason.
> 
> Any idea what can cause this?
> 
> Next steps include switching to the other Supervisor installed and/or
> downgrade IOS.
> 
> Regards
> 
> Sebastian
> 
> 
> -- 
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