[j-nsp] proxy arp C vs J

Gordon Smith gordon at gswsystems.com
Tue Feb 7 19:10:59 EST 2012

Proxy ARP can be useful while sorting out a broken (misconfigured) network,
but can also cause you a lot of grief.
If the network is configured correctly, it's just a hindrance. Most
definitely turn it off, then fix any routing issues it was masking.

I see someone mentioned turning off gratuitous arps, but I'd only do that if
really necessary, as its very useful for forcing a refresh of an entry e.g.
E-Series cable customers


-----Original Message-----
From: juniper-nsp-bounces at puck.nether.net
[mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of biwa net
Sent: Tuesday, 7 February 2012 5:57 a.m.
To: juniper-nsp at puck.nether.net
Subject: [j-nsp] proxy arp C vs J

Hi Guys
We are experiencing some issues in one of our client sites,

Basically we migrate from a Cisco to a Juniper MX80, and since there has
been some issues,  mainly we are seeing IP addresses being shared by 2-3 mac
address, to be precise , mac address being rewritten , ie: one IP is being
seen on the Juniper owned by 3 different mac address within one hour (  the
1st mac address is being re-writen by the 2nd one and then 2nd by the 3rd

This is causing a lot of users not having any kind of internet
connectivity.When we rollback to the Cisco device , this issue does not

After investigation we can safely eliminates the DHCP server being the cause
of issue (, also proved when Cisco is roll back in the topology),

The config of the Cisco is fairly simple and is almost 99.99% than the one
being copied over to the Juniper.

One thing we notice is that both Cisco and Juniper has proxy-arp configured
on some of the interface, and we are planning in our next maintenance to
disable it.

my question is: is the proxy-arp behavior in Juniper slightly different than
the Cisco ?

thanks for your inputs
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