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New Member

Routing VLANs

First off, I am new to this area of VLANs so bear with me. Here is what I am trying to do. I have a 2611XM router at my corporate office (this is all still a lab set up right now for testing). E1 I have set up as and a 2950 switch attached with VLAN 1 as the only VLAN on the switch, and a PC connected to the switch (PC E0 I have set up as with a 2950 switch attached with VLAN 2 as the only VLAN on the switch and a PC connected to the switch (PC I have trunking set up between the 2 switches. I am running EIGRP on the 2611. With all this set up, I can't ping from the PC to the PC Also I am getting a "not on common subnet" EIGRP error message. What am I missing here? Shouldn't the 2611 be able to route the 2 VLANS? Any help would be appreciated. I can provide the configs if needed. Thanks!


Re: Routing VLANs

You are getting the not on common subnet because of the trunk link between switches, so your eigrp multicast packets are leaving one interface and hitting the other, and they are on different subnets. Remove the trunk link and the messages will drop. The PCs should have a default gateway to the router's local interface, then it should work.


New Member

Re: Routing VLANs

Great! That worked. Ok, now is it possible to have both those vlans on the same switch rather than 2 switches?

Thanks for your help

Re: Routing VLANs

Yes, you have at least 3 options:

-On one switch, create 2 vlans, have vlan x connecting to port e0, and vlan y connecting to port e1. Put switch ports in appropriate vlan. Have PCs gateway pointing to ethernet port of same vlan. Downside is a wasted interface on the router.

-Create a secondary IP on e0 for the second IP range (eg and have the PCs point to the gateway. Downside is the switch sees it (ie both subnets) as all one vlan (not bad for unicast, just broadcasts).

-If it's fastethernet, create subinterfaces on one of the ethernet ports that correspond to the vlans, enable dot1q or isl trunking on the router, and trunk on the switch port that connects to the router. Uses one interface and seen as 2 vlans by switch.


New Member

Re: Routing VLANs

I really appreciate your help. The router I am using is a 2611XM with 2 fastethernet ports. I can create a subinterface, but when I try to give it an ip address, I get the following error "Configuring IP routing on a LAN subinterface is only allowed if that subinterface is already configured as part of an IEEE 802.10, IEEE 802.1Q, or ISL vLAN." I assume it is because I have to set the encapsulation to dot1q, but encapsulation is giving me an unrecognized command error? Any ideas?

Re: Routing VLANs

ISL/dot1q encapsulation is configurable on Fast Ethernet interfaces.

Router(config)# interface fastethernet 2.10

Router(config-subif)# encap isl 10 (encap dot1q)

Router(config-subif)#ip address

Router(config-subif)# exit

Router(config)# interface fastethernet 2.20

Router(config-subif)# encap isl 20

See link:

If a no go do a:

Router(config-subif)# encap ?

See what it says. Check your IOS version as well. Should be supported by your hardware but maybe may not.