[c-nsp] Quick routing question.

[Jon Lewis]

On Thu, 9 Sep 2010, Drew Weaver wrote:

> I currently have two connections to Level3 because I am upgrading, one 
> (the old one) is a 1Gbps connection in Router-1, the second one is a 
> 10Gbps connection in Router-2.
>
> Both connections are up/up, the old connection is getting a full BGP session from Level3.

I assume the new connection doesn't have BGP turned up yet?

> I noticed that no matter what I do, I can't seem to ping Level3's side 
> of our 10Gbps interface on the new connection from either of the 2 
> routers
...
> I am able to ping their side of the interface from hosts downstream from the routers, just not the routers themselves.
>
> [root at vmz ~]# ping x.x.x.13
> PING x.x.x.13 (x.x.x.13) 56(84) bytes of data.
> 64 bytes from x.x.x.13: icmp_seq=1 ttl=60 time=3.27 ms

Ah...but when you do this, are you sure x.x.x.13 is really the other side 
of your 10G connection?  This is ethernet, so when you try to ping 
x.x.x.13 from your router, it sees a route for x.x.x.12/30 via the 10G 
Level3 interface, and sends an arp request for x.x.x.13.  If Level3's end isn't 
actually configured for the /30 you are, they're not going to reply to 
that arp...and maybe the x.x.x.13 you're looking for really is in use 
somewhere else on their network?  Are you redistributing x.x.x.12/30 into 
your IGP, or might those packets be going out the old connection?

What's show ip arp on your router show you?

----------------------------------------------------------------------
  Jon Lewis, MCP :)           |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
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