[c-nsp] Strange Routing..

[Fabio Mendes]

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> 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 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, 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, 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, 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, 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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