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New Member

Secondary IP address not replying to ARP

TO change IP address I put a secondary IP address on an interface and told the clients to update their machines to the new address over the next couple of weeks. However, the first one to do so, failed. I could ping his new address from the router, but nowhere else. Using a sniffer, I saw him issue a ARP to my routers new secondary address, but no response.

To make him work, I flipped the primary & secondary desginations on the router interface. This fixed the one now on the primary, but broke all others. Why, I thought the router would reply to ARP requests for botht he primary & secondary addresses?

router config:

interface FastEthernet2/0/0

ip address secondary

ip address

no ip directed-broadcast

ip accounting output-packets

no ip route-cache distributed

Version 12.0(6a)

VIP Purple

Re: Secondary IP address not replying to ARP


which OS are your clients running ? If it is a Windows OS you might want to try and flush the ARP table with the command:

arp -f

and also the routing table with the command:

route delete *

from a DOS prompt. Do the clients have the secondary IP address as theur default gateway after changing their IP addresses ?



New Member

Re: Secondary IP address not replying to ARP

The clients do not run Windows. However, I did see them issue an ARP on the LAN for the secondary IP address of the router, so I think their config is correct ... in addition, by simply flipping the primary and secondary desgination on my router interface cured the renumbered clients.