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

Allan Leinwand allan at vyatta.com
Wed Jun 7 08:35:03 PDT 2006

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 ( should reply with a proxy ARP if it has a route to I'm assuming that this router has a directly connected route to

I would make sure that:

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

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

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

Take care,

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


  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  :
Router1:  &
Router2:    &
Router3: &
HostB  :

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 it does the following:

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


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

Same is the case in the opposite direction

I ran tcpdump on the interface on Router1 and it is getting arp 
arp who-is tell

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 being sent out by the host ( ?

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



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