Putting 2 fastethernet together of router

Unanswered Question
Sep 24th, 2007

Hi,

We are using 1841 with one serial and two fastethernet ports for internet connectivity.

We are using NAT in router for users accessing our internal resourses from internet. For NAT we have configured NAT inside and NAT outside commands on fastethernet(0/0) and serial(0/0/0) interface respectively. So far so good it works fine.

But as a redundancy we plan to use second ethernet port also. Thus we plan to add this fastethernet (0/1) with fastethernet (0/0) so that we will be able to connect two different ports to two different switches. After these swicthes there is firewall configured in a failover mode with outside interface connected to these two seperate swicthes.

Can such clubbed interface ( fa0/0 and fa0/1) will form a HSRP with another router with similar or same configuration ( fa0/0 and fa0/1 clubbed together to form a single interface ).

In IBM AIX language this kind of clubbing on ethernet ports is "TEaming of ports".

Any similar activity experience Please share any link on cisco.com ?

Thanks and REgards

Subodh

I have this problem too.
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Richard Burts Mon, 09/24/2007 - 10:13

Subodh

It may be that I do not fully understand what you are describing. When you talk about connecting the two FastEthernet interfaces to two different switches are these in the same VLAN or in different VLANs?

Cisco IOS will not allow two Ethernet interfaces of the same router to be configured in the same subnet (in the same VLAN). If you really want to use both interfaces in the same VLAN then your alternative is to configure Integrated Routing and Bridging. In IRB neither FastEthernet interface has an IP address. You configure a bridge group and assign that bridge group to each interface to enable bridging on both interfaces. You then configure a BVI interface which is in the bridge group and the BVI has the IP address. This enables both interfaces to share the same IP address. Note that only one interface will be active at a time. It does provide redundancy.

HTH

Rick

bapatsubodh Mon, 09/24/2007 - 18:31

Hi,

Both ethernet are in same vlan ( in fact vlan 1 default ).

I will post a diagram of our setup please share ur experience with similar setup.

Thanks and Regards

Subodh

Richard Burts Tue, 09/25/2007 - 04:06

Subodh

I have no direct experience of implementing this. And I would not recommend it. I am not convinced that any benefit of having 2 FastEthernet interfaces on the same router in the same VLAN is worth the complexity that it introduces. But if you (or if your management) has decided that you want both interfaces to be active in the same VLAN then the solution with IRB that I described is the way to do it.

HTH

Rick

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