[c-nsp] Quick routing question.

Drew Weaver drew.weaver at thenap.com
Thu Sep 9 13:09:59 EDT 2010


I assume the new connection doesn't have BGP turned up yet?
Correct, I am just trying to get it to where I can ping it first (which is what I usually do, anyway).

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?  
All valid points, when I trace route to .13 from the host that can ping it I see:

[root at vmz bin]# tracert x.x.x.13
traceroute to x.x.x.13 (x.x.x.13), 30 hops max, 40 byte packets
 1  gw (gw)  0.486 ms  0.458 ms  0.463 ms
 2  core (core)  0.460 ms  0.710 ms  0.709 ms
 3  rtr (rtr)  0.427 ms  0.428 ms  0.425 ms
 4  x.x.x.Level3.net (x.x.x.13)  3.238 ms  3.238 ms  3.236 ms

However, I can't know whether the return traffic is coming back in on that connection, or not.

Are you redistributing x.x.x.12/30 into 
your IGP, or might those packets be going out the old connection?
Yes, and see above.

What's show ip arp on your router show you?
rtr#sh ip arp
Protocol  Address          Age (min)  Hardware Addr   Type        Interface
Internet  x.x.x.14              -   xxxx.xxxx.a9dc  ARPA        GigabitEthernet2/1/0
Internet  x.x.x.13             14   xxxx.xxxx.4d7a  ARPA        GigabitEthernet2/1/0
Internet  x.x.x.12              -   xxxx.xxxx.a9dc  ARPA        GigabitEthernet2/1/0

(Ignore the 'gigabit' part, on 12000s for some reason they never changed the interface names).


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