use broadcast messages to add ARP table entries

m4rtin · 11-10-2012, 06:53 PM

Is it possible to configure Linux kernel(I guess it depends on TCP/IP stack) to use broadcast messages for building up ARP table? I mean for example I have two hosts PC1 and PC2 in the same broadcast domain and both hosts have empty ARP table. Now if I execute "ping -b -c1 10.10.10.255" in one of the hosts, then other receives:

Code:

02:34:35.783967 00:1a:6b:6c:0c:cc > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 98: 10.10.10.2 > 10.10.10.255: ICMP echo request, id 8297, seq 1, length 64

Technically it could add association between 00:1a:6b:6c:0c:cc and 10.10.10.2 to it's ARP table but it does not. I guess this behavior is turned off in order to avoid huge ARP tables in case of large broadcast domains? Is there a way to use broadcast messages to add ARP table entries? I use 2.6.32-5-amd64 Linux.

unSpawn · 11-11-2012, 12:58 PM

Quote:

Originally Posted by m4rtin

Is it possible to configure Linux (..) to use broadcast messages for building up ARP table?

Broadcasts are the way for populating the ARP cache AFAIK.

Quote:

Originally Posted by m4rtin

I have two hosts PC1 and PC2 in the same broadcast domain and both hosts have empty ARP table.

If with "broadcast domain" you mean the same network segment then I would first wonder what would be wrong with these hosts or their settings. (BTW 'arp -a' doesn't produce as much detail as 'ip -s n ls'.) If you have fixed MAC - IP mappings then you could use static ARP entries in /etc/ethers.

BTW thanks for mentioning Cloudshark in your other post. Good to know such a service exists.