Eigrp and two different vlans between the same L3 switches

[Ruterford]

Hi,

I have a following situation:

Switch1 is connected  to Switch2 with a trunk port.

Vlan 10 is allowed in the trunk port and set as "no passive-interface" for EIGRP 10.

Now I need to add another router in the different Vlan(cannot use Vlan 10) and advertise its networks in EIGRP 10.

So I have added Vlan 20, put it in "no passive-interface" mode in EIGRP 10,  applied access port for the new router and configured advertising of router's routes in EIGRP 10 on the router. Switch1 and Switch2 are actually HSRP nodes with the same networks advertised on both ends.

The networks from the router are advertised and I can see them in Switch1 and Switch2 in EIGRP 10,but my question is that now I see the routes previously being advertised from Switch 1 to Switch 2 thru vlan 10, now being also advertised thru Vlan 20 with equal cost. Basically Vlan 10 and Vlan 20 are in the same trunk, so I think this is not a big deal these networks are now advrtised over two Vlans with the same cost, but I am just curious maybe I am missing something and you can see some possible problems due to this change.

Thanks!

[Marwan ALshawi]

is the router multi homed/connected to both switches ?

if not it is better to connected to both as you mentioned the switches running HSRP and if one switch thats connect to the router goes down then you will lose connectivity to the router

about eqaul cost it is not a probelm if you wanted like this

but if you have your switches working in active standby it is better to have each switch to prefer the link directly connected to the router so that when the switch receive the traffic it will go directly to the router rather than spaning the inter-switch link

Hope this help

if helpful Rate

[Jon Marshall]

It is not a problem to have the 2 L3 switches peering over multiple vlan interfaces. After all the interconnect is sill the same trunk.

An example would be when you setup a pair of 6500 switches for all inter-vlan routing and run a dynamic routing protocol such as EIGRP between them. All the vlan interfaces will peer with their respective vlan interface on the other switch. Usually you would make all vlan interfaces except 2 passive to cut down on the number of peerings.

What's not clear from your setup is whether the router you added in vlan 20 is the default-gateway for clients in vlan 20. If it is then you can only set it up the way you have. If however vlan 20 has vlan interfaces on the L3 switches and you run HSRP for vlan 20 on the L3 switches then another solution would be to simply connect the router to the switch(es) using routed ports and then you don't have the vlan 20 issue eg.

router

=====

int gi0/1

ip address 192.168.5.1 255.255.255.0

switch

=====

int gi0/1

no switchport  <-- this removes the port from any vlan

ip address 192.168.5.2 255.255.255.0

you can still peer between the router and the switch with EIGRP but you are not using vlan 20 to do it.

However as i say this may not be the best solution for what you are trying to do.

Jon