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New Member

2621 Ethernet Interfaces both on same subnet?

Hi,

This is a bit tricky.

1) Is it possible to configure both of the fixed ethernet ports on a 2621 router to be connected to the same subnet?

i.e

interface Ethernet0/0

ip address 192.168.3.8 255.255.255.0

interface Ethernet0/1

ip address 192.168.3.18 255.255.255.0

2) Once this is done is it possible to configure a second router in the same way and implement HSRP between the two routers?

My goal is to set up a Redundant LAN that duplicates all hardware (2 switches, 2 routers, 2WAN links) but only contains one single LAN subnet. For each of the LAN hosts I am using two special network adapters that support "Fault Tolerance" whereby a failure in one cable or one of the switches is automatically detected by the network interface and then the standby interface is started. I am basically trying to do the same thing on the routers.

Thanks in advance.

AM

6 REPLIES
Bronze

Re: 2621 Ethernet Interfaces both on same subnet?

If you bridge between the two interfaces than it's possible. If you want to route

you need one or more subnet per interface.

Hope that was you question.

Roger

New Member

Re: 2621 Ethernet Interfaces both on same subnet?

I'm not bridging between the two interface. I accidentally entered the question without entering the details of my question. Much more detail is now included. Sorry.

Bronze

Re: 2621 Ethernet Interfaces both on same subnet?

Hello

To question 1.....it's not possible. You can try to implement it but the router does not let you configure the same subnet on different interfaces.

2) I probably don't understand you all the way....but is it not enough if you have

two routers in the same subnet an run a HSRP between the routers for the redundandency out of the LAN?

As you can not implement the same subnet on two differnet interfaces on the same router you could use may be two different subnets?!

Ciao

Roger

New Member

Re: 2621 Ethernet Interfaces both on same subnet?

Hi,

Thanks for the response.

Regarding question 2) I cannot do it the way you suggested as I want to avoid using the backup router (slower WAN link) in the event of a LAN switch failure. I only want to use it if the main router fails.

thanks.

A.

Bronze

Re: 2621 Ethernet Interfaces both on same subnet?

Hi,

Maybe you could solve this problem with a back-to-back connection between

the two routers with a crossed ethernet cable. But the router schould be close

together.

So in case of HSRP ist aktiv on the "slower router, let's say because of some

switch failure, and the "faster router" is still running you could implement you routing so the data will use the back-to-back connection and go over the fast wan connection of the "faster router".

Ciao

Roger

New Member

Re: 2621 Ethernet Interfaces both on same subnet?

Hmmmm. Your suggestion has some merit. Thanks.

I now intend to seperate the WAN links across the two routers and make all of them faster WAN links and also to disable HSRP. Therefore, no backup WAN links. Just two seperate routers.

I am proposing connecting the two 2621 routers back-to-back with a x-over ethernet cable (on a different subnet to the switch-conected interfaces) and have their second ethernet interfaces on the routers connected to the two LAN switches (on the same subnet). Therefore, if there is a failure in a switch, router A's ethernet interface will fail, but packets might be routed through the back-to-back connection of router B to the WAN links on router A. I intend to use RIP v2. Does what I describe sound acceptable?

Thanks again,

regards,

A.

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