Interesting Situation

[corey.mckinney]

Scenario:

I have 2 routers at a location. The ethernet interfaces are on the same subnet. The serial interfaces go to seperate locations. Currently, I have everything on the ethernet subnet routing to one of the routers and that router will then determine if it needs to route to the other router.

What I would like to do is have a virtual IP address that both routers will respond to and then which ever one has the route to the destination, that router will take it.

Can this be done???

Thank you in advance.

[Richard Burts]

Corey

What you describe sounds almost (but not quite) like HSRP. In HSRP there is a virtual address which the routers share. The end stations configure that virtual (shared) address as their default gateway and forward to it. But you are describing a situation where both routers actively receive packets sent to the shared address and in HSRP one of the router is active on the shared address and the other router is standby.

I do not know of a way to achieve what you are describing. It seems to me that there are a couple of issues in doing what you describe. What would happen if both routers receive the packet and both routers have a route for the destination? What would happen if both routers receive the packet and neither router has a good route for the destination?

I believe that the optimum solution is to use HSRP.

HTH

Rick

[rafaelgarcia]

Hi,

I believe I understand what you are trying to do. HSRP won't suit your purposes since it is used to create redundancy.

Now, I have seen other people that use IP Redirect for this implementation. Basically, IP Redirect tells the host what router has the best route to the destination it is trying to reach. There are some security concerns when using IP Redirect.

I hope it helps.

[kamlesh.sharma]

Hi corey Mckinney,

rburts what you have explained is true for HSRP that only one router will forward the packet at time.well we have tracking facility in HSRP to trach interface as well it will work for you.

please rate if helps

HTH

kamlesh

but i have another design to do load share what if i put router 1 ip address say for example 1.1.1.1 as default gateway in 50% machines and router 2 ip address 1.1.1.2 as DG in 50 % machine and in all the machine we will have secondary default gateway as virtual ip address 1.1.1.254.

so in case of router1 goes down 50 % machine will do an ARP for virtual ip address whichever router is master will reply back to that ARP.

Will it work like i am thinking.

please rate if helps

HTH

kamlesh

[jstoecker]

Corey,

Just thinking out loud, so to speak...

I would say that if avoiding ICMP redirects is a high priority, you might consider what it would take to "smarten up" your traffic sources on that ethernet subnet, so that they know which router IP to forward to, or figure out a way to move the 2nd link onto the first router (assuming that administrative and/or configuration issues don't prevent the latter).

"Smarten up" could be running a routing protocol shared with the two routers (has its pluses and minuses, but if the ciscos only source the routing information and never accept any back from those machines it might not be too bad - rip ver2, maybe?) or static routes if the number of hosts / destination networks is limited (hmmm, static routes in hosts are not one of my favorite things - but if the devil drives...).

John

[Ian Wilson]

HSRP supports ICMP redirects from 12.2 onwards.

You could setup two HSRP groups - one Active for each router. Split your hosts such that half have one HSRP IP address and half have the other HSRP IP address.

Ensure ICMP redirects are enabled. ICMP will coordinate with HSRP such that hosts are redirected to a virtual IP address.

For example, lets say host A has def gw of HSRP 1, and HSRP 1 is Active in rtr 1. If the hosts sends a packet to a destination that is of off rtr 2 then rtr 1 will redirect that host to the HSRP virtual IP address that is Active in rtr 2.

Thus you get the benefit of both ICMP redirects *and* the redundancy provided by HSRP.

Ian