Inter vlan routing dilemma

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May 28th, 2007
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Hi all.I have a slight dilemma regarding VLANs and inter network routing.I have a network in which there are 2 routers and 2 3750 switches (with standard images on them connected over a trunk).

I need to implement VLANs on the switches and I'm thinking of using one of the following options:


1. enabling RIPv2 routing on one 3750 switch and on the routers since there will be a few VLANs


2. using one of the routers in the router on a stick configuration to do the inter VLAN routing for the network using EIGRP.


My dilemma is if I use the 1st option as the network grows RIPv2 will become impractical and if I use the 2nd option the router will possibly have additional subinterfaces created and I'm not sure if it will be able to cope with so many subifs.BTW routers are 2811 and 2821.

Any advice?


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ankbhasi Mon, 05/28/2007 - 08:01
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Hi Friend,


May be I am not very clear with your question so I will like to know more about your network. Can you confirm you want to enable EIGRP in option 2 and RIPv2 in option 1 for inter-vlan routing or to make your vlan subnets to talk to your other network where you have rip or eigrp?


In your second option you are concerned about subinterfaces on your router so I will say do not worry about the same as it will have good enough to support your number of vlans. It depends upon interface IDBs.


Have a look at this link which will give you an idea about number of IDBs supported on

different router platorm


http://www.cisco.com/warp/public/63/idb_limit.html#addtl_idb_limitsisr


HTH


Ankur


*Pls rate all helpfull post

Amit Singh Mon, 05/28/2007 - 08:03
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What is your overall topology. Is it something like this


Topology 1 :


Switch1----link---Router1---WAN LINK----Router2-----Link---Switch2


Topology 2 :


Switch1----Trunk---Switch2---- Router1 and Router 2 connected to the switches.


In case1, I would suggest to do the intervlan routing on 3750 switches at each site and run RIPv2 on 3750 and routers to advertise all the routers.


In case 2, I would still still suggest you do inter-vlan routing on 3750's only and run RIPv2 to advertise all the routes to routers. You cannot use EIGRP on 3750's as you are running standard image on them.


You can either upgrade the 3750's to enhanced image to support advanced routing protocol. If you want to use EIGRP on routers using a router on stick config, then it should be Ok as router can support a lots of sub-interfaces.


I would not suggest to go for option 2 as when your network will grow you will again see a lots of challenges in scaling the network in this design. With the advent of L3 switches, the design always suggest to have interlvan routing done on the L3 switches and run a routing protocol across your routers to advertise the routing updates end-end.


HTH,Pleae rate if it does.

-amit singh



IgorHamzic Mon, 05/28/2007 - 10:08
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Topology 2 is the topology I have.I see now that I haven't been too clear in my explanation.Sorry for that.There will also be two ASA's in failover connected to the switches but thta's another matter.


So you are suggesting that doing RIPv2 inter vlan routing and then advertising the routes from the 3750's to the routers is better than doing the router on a stick configuration.

Thanks for the advice.I wasn't sure which one would be better.


One more question though.Wouldn't it be better to run RIPv2 just on one switch and let the other just connect to it over a trunk and rely on it for inter vlan routing.I don't think it would work if I enable the same VLAN interfaces on both routers.Or am I wrong?

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