[c-nsp] Strange Routing..

Howard Leadmon howard at leadmon.net
Tue Nov 22 20:08:17 EST 2016


  OK, this is even crazier, and now I may never find it.   After updating and restarting the router this issue happened, but I found out I forgot one of the prefix lists to a peer, so thought OK, let’s be safe and just reload the BGP configs I had stored to be safe.   After doing that reload, the local route vanished as mentioned before, and now everything is showing clean:

 

#sho ip route 206.126.237.0 

Routing entry for 206.126.237.0/32, 1 known subnets

  Attached (1 connections)

  L        206.126.237.136 is directly connected, Vlan99

 

 

I guess the change caused it to update the fib, and it seems to be working right.

 

I ran the command as you requested Fabio, but of course now it looks fine..

 

#show ip cef 206.126.236.37 detail

206.126.236.37/32, epoch 8, flags attached

  Adj source: IP adj out of Vlan99, addr 206.126.236.37 4C4BADE0

   Dependent covered prefix type adjfib, cover 206.126.236.0/22

  2 RR sources [heavily shared]

  attached to Vlan99

 

Would love to know what happened, but at the moment guessing I’d be chasing my tail..

 

 

---

Howard Leadmon 

PBW Communications, LLC

http://www.pbwcomm.com

 

From: Fabio Mendes [mailto:fabio.mendes at bsd.com.br] 
Sent: Tuesday, November 22, 2016 7:59 PM
To: Howard Leadmon <howard at leadmon.net>
Cc: Cisco Network Service Providers <cisco-nsp at puck.nether.net>
Subject: Re: [c-nsp] Strange Routing..

 

What does a 'show ip cef detail' return for those?

 

 

 

On Tue, Nov 22, 2016 at 7:15 PM, Howard Leadmon <howard at leadmon.net <mailto:howard at leadmon.net> > wrote:

  OK, and in my terrible lack of sleep maybe I am missing something that I
shouldn't be, but here is the issue..



I have a 7606 with RSP720's running IOS 15.3(3)S6 at this time.  Across the
Ashburn exchange they use the IP block of 206.126.236.0/22 <http://206.126.236.0/22>  for peering.  If I
look at the router and ask it for the routing for this block I see:



#sho ip route 206.126.236.0

Routing entry for 206.126.236.0/22 <http://206.126.236.0/22> , supernet

  Known via "connected", distance 0, metric 0 (connected, via interface)

  Routing Descriptor Blocks:

  * directly connected, via Vlan99

      Route metric is 0, traffic share count is 1





My IP in use on the exchange is 206.126.237.136



So if I run a show route on a few peers we connect with, I would expect it to
fall inside the above supernet, and if they are in .236, .238, or .239 they
do, but not if they are part of .237.    As an example:



#sho ip route 206.126.236.37

Routing entry for 206.126.236.0/22 <http://206.126.236.0/22> , supernet

  Known via "connected", distance 0, metric 0 (connected, via interface)

  Routing Descriptor Blocks:

  * directly connected, via Vlan99





.236 is good..



#sho ip route 206.126.237.37

% Subnet not in table



.237 is bad..



#sho ip route 206.126.238.37

Routing entry for 206.126.236.0/22 <http://206.126.236.0/22> , supernet

  Known via "connected", distance 0, metric 0 (connected, via interface)

  Routing Descriptor Blocks:

  * directly connected, via Vlan99



.238 is good, as well at .239..



If I look at the routes I see the router seems to be injecting a local /32
which doesn't make a lot of sense to me either:



#sho ip route 206.126.237.0

Routing entry for 206.126.237.0/32 <http://206.126.237.0/32> , 1 known subnets

  Attached (1 connections)

L        206.126.237.136 is directly connected, Vlan99



 This is causing connection issues for some of the peers for sure, and a
static route for the /24 will add it to the routing table, I am at a total
lost as to why it's not already present with the /22 in the table, and with
the fact the interface to the IX shows with a mask of 255.255.252.0.   All of
my IPv6 is great, just this one issue with IPv4 driving me batty.



Any suggestions or advice most welcome..





---

Howard Leadmon

PBW Communications, LLC

 <http://www.pbwcomm.com> http://www.pbwcomm.com



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