Router Backup Interface

[l.aviv]

Hi,

I have a router with 2 lan interfaces.

I need to define a backup interface (LAN) for the same IP address as the primary one.

Is it possible? How?

thank's

Lior

[vkasacavage]

I do not believe this is possible. The router should prevent you from using the same IP address on another interface. HSRP will perform similar functionality to what you are trying to do

[l.aviv]

What about using the backup interface command?

[tselvan]

Hi,

I have assigned the same ip address to two ethernet interfaces of cisco 7200 router using the back up interface command.But when the active link goes down,standy link doesnot come up automatically. This issue to due to ARP.When i delete the ARP in the PC,this is possible.

Can anyone help me out to solve this problem.

tselvan

[DALE FRANCIS]

The best bet has been mentioned, is to use the HSRP as it can provide laod balancing capabilites with MHSRP etc..

[l.aviv]

But, can I use the HSRP on the same router?

an d what if I have two routers with tha same configuration?

[DALE FRANCIS · Accepted solution]

These two router's will be on the same wire/segment.

Depending on what platform you can configure mutiple groups on a single interface. The simplest way is to config

R1 - Active

standby 1 priority 140 preempt

standby 1 authentication LAB

standby 1 name Live_Net

standby 1 ip 10.1.10.254

R2 - Standby

standby 1 priority 110 preempt

standby 1 authentication LAB

standby 1 name Live_Net

standby 1 ip 10.1.10.254

In the above R1 is active and if this interface fails then, R2 will flip over and resume traffic flow, You can also configure multple groups on an interace eg:

Int VLAN 10

standby 2 priority 140 preempt

standby 2 ip 10.1.10.200

standby 1 priority 110 preempt

standby 1 ip 10.1.10.254

So on once side active IP will be the end users Default G/W of 10.1.10.200 and the the other end the Default G/W will use 10.1.l0.254, so this creates a load balancing scenario

You could also track other interafaces on a router with "standby 1 track"

[subbarao.s]

Hi,

How about using the same MAC Address on both the interfaces? I think this works? PC Does not require ARP entry to timeout.

If something rellay restrict you from configuring HSRP, you can go ahead with setting same MAC Address manually, this should work.

Regards,

[tselvan]

Hi subbarao,

Thanks for the information.I assigned the same mac address,it works fine.

Rgds,

tselvan

[9mmurphy]

One note to make, standby will decrement the priority by 10 points by default. If you track an interface, with the priority different by 30 points, it will not switch over to the standby interface. It will work during a complete failure of the interface, because of the lost communication between interfaces. A value of 5 points difference will cause the priority feature to function properly.