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?

I have this problem too.
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mahmoodmkl Sat, 03/24/2007 - 01:21

Hi

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 1.1.1.2 255.0.0.0 secondry

Thanks

Mahmood

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.

Router

f0/0

ip address 10.0.0.1 255.255.255.252

ip address 192.168.1.1 255.255.255.0 seecondary

ip address 192.168.2.1 255.255.255.0 seecondary

ip address 192.168.3.1 255.255.255.0 seecondary

ip route 172.16.5.0 255.255.255.0 192.168.1.2

ip route 172.16.3.0 255.255.255.0 192.168.3.2

Please rate if your question is answered

Regards

S. Shantharam

Attachment: 
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 172.16.1.0 255.255.255.0 <---existing

ip address 192.168.1.0 255.255.255.0 SECONDARY <---adds additional address block

ip address 10.1.1.1 255.255.255.0 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

Scott

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

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

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