any limit to number of secondary ip addresses?

[rachelhor]

Hi,

Is there any limit to the number of secondary ip addresses on an interface of a router?

I just took over an existing live system.

The previous engineer configured secondary ip addresses on a single physical interface.

Currently, there are 1 main ip address and 2 secondary ip addresses.

I am not allowed to change the existing configuration nor disrupt the existing live system, so I cannot use sub-interface.

When I tried to add 1 more secondary ip addresses, to make it 1 main ip and 3 secondary ip address,

but no matter how I tried, I cannot ping to the end device of this NEW secondary ip address subnet

So I removed one of the existing secondary ip address, I discovered I can ping to the end device of the NEW seconday address!!!

But when I put back the one I removed, I can no longer ping to the end device of the NEW secondary address AGAIN!

I suspect that there is a limit to the number of secondary addresses that can be configured on the physical address.

But, I check the link http://www.cisco.com/en/US/tech/tk365/technologies_q_and_a_item09186a008012d8f7.shtml#q21, it says

Q. What are the maximum number of secondary IP addesses that can be configured on a router interface?

A. There are no limits on configuring secondary IP addresses on a router interface. For more information, refer to Configuring IP Addressing.

I think Cisco could be wrong when saying "There are no limits".

Can someone kindly help me confirm whether there are any limits to the number of secondary ip addresses on an interface of a router?

thank you

[sachinraja]

Hello rachel,

I havent seen any limit to configuring secondary IPs. Are you sure that the new IP subnet is not over-lapping or merging with some other subnet on the router or LAN ? Normally, your scenario should work. Please let us know.

Regards

Raj

[rachelhor]

Hi,

The main ip and secondary ip addresses are all subnetted into 255.255.255.240.

Main IP 172.16.21.155

Secondary IP#1 = 172.16.21.141

Secondary IP#2 = 172.16.21.93

New Secondary IP#3 = 172.16.21.226

As a test, I simply remove any of the existing secondary ip addresses, and it works!

But when I put back any of the addresses I removed, the new one does not work again.

If it is ture there is no limit, can it be due to other factors like the router hardware?

Pls kindly advice.

Thank you.

Rgds,

Rachel

[glen.grant]

I would check your masking in your configs and on your client that you are trying to ping , these should not be overlapping. also make sure your default gateway on the client is correct .

[Richard Burts]

Rachel

I have seen routers configured with 16 secondary addresses and they work without problem. Without knowing specifics of what platform, what release version and what feature set you are running on your router we can not know for sure. But I am pretty positive that you are not having an issue based on a limit on the number of secondary addresses.

It would be helpful if you would post the actual interface configuration from the router and also the output of ipconfig (or maybe ipconfig /all) from the PC. This might give us better insight into what is happening.

HTH

Rick