[Xorp-users] ARP problems with static routes in XORP

[Allan Leinwand]

Hi Vikram,

   It looks like your host may be doing the right thing, depending on how you have your default gateway set up. The host is sending an ARP for the destination IP address and the router (17.17.17.1) should reply with a proxy ARP if it has a route to 10.1.1.2. I'm assuming that this router has a directly connected route to 10.1.1.0/24.

I would make sure that:

1) the host has a default gateway set to 17.17.17.1.  You can use netstat -r (Linux/Win) and check for the presence of a 0.0.0.0/0 route to 17.17.17.1.

2) the router has a connected route to 10.1.1.0/24 (my assumption on your subnet mask)

3) the router at 10.1.1.2 has a route (static or RIP derived) back to 17.17.17.0/24 (again, I'm assuming you're using a /24 here again).


Take care,

Allan
Vyatta, Inc.

----- Original Message -----
From: Vikram KAUL <vkaul at research.telcordia.com>
To: xorp-users at xorp.org
Sent: Wednesday, June 7, 2006 8:17:39 AM GMT-0800
Subject: [Xorp-users] ARP problems with static routes in XORP


Folks,

  I need help with a skeletal XORP setup with 3 routers and two hosts. I am 
seeing the problem with static routes as well as with RIP, so I will just 
describe the static case, and hope I can resolve the problem

  The network is laid out like follows


   17.17.17.x    10.1.1.x    192.168.0.x      16.16.16.x

H ---------- R ---------- R ------------- R ----------- H
.20       .1  .1       .2   .2          .3  .3         .20


HostA  : 17.17.17.20
Router1: 17.17.17.1  & 10.1.1.1
Router2: 10.1.1.2    & 192.168.0.2
Router3: 192.168.0.3 & 16.16.16.3
HostB  : 16.16.16.20

When I configure XORP for static routes (or even RIP), the unicast tables 
appear properly in the routers (1,2,3). I am able to ping and traceroute 
from one to the other without any problems

Then, when I connect the host (HostA) and configure the default gw to be 
17.17.17.1 it does the following:

Ping from 17.17.17.20 (host) to 17.17.17.1 (gw router) is OK
Ping from 17.17.17.20 (host) to 10.1.1.1   (gw router, next interface) is OK

But

Ping from 17.17.17.20 (host) to 10.1.1.2 (next hop after gw) FAILS

Same is the case in the opposite direction

I ran tcpdump on the 17.17.17.1 interface on Router1 and it is getting arp 
queries
arp who-is 10.1.1.2 tell 17.17.17.20

Why is this happening ?
Shouldn't the host merely send the ping packet to the gw router which 
should then forward it to the next hop and get the reply back in the same 
way ?

Why is arp for 10.1.1.2 being sent out by the host (17.17.17.20) ?

Is this a configuration issue at the host ? or something in XORP ?

Thanks

Vikram

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