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3640 with Dual Ethernets on the same subnet

I have a 3640 that I want to use for a new site. It has two Ethernet ports that I would like to use for load balancing and redundancy. The Lan will have one subnet since it is a small office. I've tried to put both interfaces in the same subnet but I am getting a subnet overlap message when I try.

1 ACCEPTED SOLUTION

Accepted Solutions

Re: 3640 with Dual Ethernets on the same subnet

You can use IRB to get around this issue.

Sample config:

bridge irb

bridge 1 protocol ieee

bridge 1 route ip

interface ethernet0

no ip address

bridge-group 1

no shut

interface ethernet1

no ip address

bridge-group 1

no shut

interface bvi1

ip address x.x.x.x y.y.y.y

(other interface commands you're using)

no shut

6 REPLIES

Re: 3640 with Dual Ethernets on the same subnet

You can use IRB to get around this issue.

Sample config:

bridge irb

bridge 1 protocol ieee

bridge 1 route ip

interface ethernet0

no ip address

bridge-group 1

no shut

interface ethernet1

no ip address

bridge-group 1

no shut

interface bvi1

ip address x.x.x.x y.y.y.y

(other interface commands you're using)

no shut

New Member

Re: 3640 with Dual Ethernets on the same subnet

If the router is connected to a switch (not a hub), and the interfaces support it, you can also configure etherchannel between the router and the switch. This is likely to be more more efficient than IRB (although IRB will work). Configure etherchannel on the 3640 as per... interface Port-Channel N ip address a.b.c.d m.a.s.k ! interface fastethernet1/0 no ip address channel-group N ! interface fastethernet1/1 no ip address channel-group N Configuring the switch depends on whether the switch runs CatOS or IOS. For CatOS... set port channel 3/1,3/2 on For IOS-based switches it's similar to the router.

Hope this helps.

New Member

Re: 3640 with Dual Ethernets on the same subnet

I'll give that a try. Thanks for the help.

J. Caulder

New Member

Re: 3640 with Dual Ethernets on the same subnet

The router is connected to a switch, a 3524XL. I found references for port-channeling on CCO but the router does not support it from what I can tell or I'm not at the correct IOS because I don't have the command when I'm in config mode. The router is currently at 12.2(10b) IP Plus. Also, the interfaces are Ethernet (10M) only.

Thanks, J.

Re: 3640 with Dual Ethernets on the same subnet

I believe Etherchannel (Port-Channel) is only available on higher end routers (7200, 7500, etc).

New Member

Re: 3640 with Dual Ethernets on the same subnet

Unfortunately, I understand that ether-channel is not supported on simple 10BaseT interfaces. It requires 100BaseTX interfaces to do this.

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