Explanation required for the secondary address behavior

ambi · ‎09-03-2007

I just tried pinging to the broadcast address of a subnet to see how many hosts reply to it.

I saw some replies from IPs that were other the subnet. when i checked the L3 configuration i saw a secondary address associated with the interface but i am unable to understand the behavior

router#p 172.16.56.255

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.16.56.255, timeout is 2 seconds:

Reply to request 0 from 172.16.56.2, 8 ms

Reply to request 0 from 144.12.16.208, 8 ms

Reply to request 0 from 144.12.16.14, 8 ms

Reply to request 0 from 172.16.56.4, 8 ms

Reply to request 0 from 172.16.56.3, 8 ms

Reply to request 0 from 144.12.16.3, 8 ms

Reply to request 1 from 144.12.16.208, 4 ms

Reply to request 1 from 144.12.16.14, 4 ms

Reply to request 1 from 172.16.56.4, 4 ms

Reply to request 1 from 172.16.56.6, 4 ms

Reply to request 1 from 172.16.56.3, 4 ms

Reply to request 1 from 144.12.16.3, 4 ms

layer 3#sh run int vlan 1

Building configuration...

Current configuration : 222 bytes

!

interface Vlan1

ip address 172.16.56.5 255.255.255.0 secondary

ip address 144.12.16.14 255.255.255.0

no ip redirects

no ip unreachables

end

thanks in advance

Edison Ortiz · ‎09-03-2007

They may be different IP subnets but they are both in the same broadcast domain (Vlan1).

If you take a packet trace, you will see the destination MAC for 172.16.56.255 is ff:ff:ff:ff:ff:ff

All hosts within that broadcast domain will process that packet.