use of secondary address in router interface

Unanswered Question
Mar 24th, 2007

How can we use the secondary address in a router interface ? How does it work ? What is the command to configure the secondary address in a router interface?

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Overall Rating: 3 (3 ratings)
mahmoodmkl Sat, 03/24/2007 - 01:21


The usage of secondry address depends upon u r requirement.i.e during IP migration etc.

u can use the below commands to configure it.

int f0/0

ip address secondry



shantharam.sury... Sat, 03/24/2007 - 04:38

Hi Manoj,

Any device you are connecting directly below Router or L3 switch you have to add primary address

Attached Image and below config will guide you.



ip address

ip address seecondary

ip address seecondary

ip address seecondary

ip route

ip route

Please rate if your question is answered


S. Shantharam

scottmac Sat, 03/24/2007 - 08:27

The primary use for secondary addressing is for address migration, for example:

Your company wants to re-do their addressing, perhaps to make it more hierarchical for the purpose of proper summarization, or to expand the node count.

Both address blocks can be assigned *** TEMPORARILY *** to one interface, so that the clients can be migrated in phases and still have be be able to access all of the network resources. Once the clients are migrated, the SECONDARY addressing should be removed from the interface.

SECONDARY addressing is considered a security risk, it can screw up some routing protocols, and unnecessarily complicates the operation and administration.

SECONDARY addressing should not be used for anything other than temporary, "band aid" workarounds until the ultimate solution can be implemented.

To use it, just add an additional address command to an existing interface:

ip address <---existing

ip address SECONDARY <---adds additional address block

ip address SECONDARY <-----Adds a third address block

You can have any number of additional SECONDARYs, but remember, it's not meant to be anything but a temporary solution.

Good Luck


manojkumarnb Sat, 03/24/2007 - 22:31

Thanks, this information is very knowledgable and very useful. Thanks once again.


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