Fast ethernet interface redundancy

[jasonjoanne]

Gentlement,

I have one router 2621 with 2 fast Ethernet interface. my questions as below:

1) Could i configured 2 fa interface with same IP address for redundancy.

2) if can, how to configure it?

Thanks

[attrgautam]

No you cannot redundancy with the same iP address on FE (atleast in global routing table). You could if u used vrf lite.It doesnt allow you to configure the same IP address on both interfaces.

[jasonjoanne]

Hi,

Thanks for your informations. and I have few questions again:

1) Do I need 2 routers for running HSRP? How about one router with 2 interfaces?

2) How to configure the 2 routers for running HSRP and the cable connection between the 2 routers becasue I only have one E1 line.

Thank you

[spremkumar]

hi

Itz not possible to configure the same ip on 2 fast ethernet interfaces,instead configure 2 different ip address and configure 2 default gateways in your PC.

The primary default gateway without any metric and the secondary one with metric.

regds

[ankurbhasin]

Hi Friend,

You cannot configure 2 fa interface on same router with same ip address nor you can have same subnet ip for 2 interface on same router.

If you try to configure you will get overlapping ip address error message.

If you have 2 routers then you can configure them using same subnet ip address but again not with same ip address and can have same standby ip address on both the interface on 2 routers (HSRP) and can make one router fa interface active and second fa interface on secoind router as standby but this is not possible on same router.

HTH

Ankur

[jasonjoanne]

Hi,

Thanks for your informations. and I have few questions again:

1) Do I need 2 routers for running HSRP? How about one router with 2 interfaces?

2) How to configure the 2 routers for running HSRP and the cable connection between the 2 routers becasue I only have one E1 line.

Thank you

[Richard Burts]

1) Yes you need 2 routers to run HSRP. HSRP requires 2 layer 3 interfaces in the same subnet and in the same broadcast domain. The IOS will not allow 2 interfaces on the same router to be configured as layer 3 interfaces in the same subnet. So 2 interfaces on the same router will not work for HSRP.

2) I do not understand your question here. If you are saying that you have only 1 E1 line then you can have only 1 router with the outbound connection and HSRP is not much use for that situation.

HTH

Rick

[jasonjoanne]

Rick,

Sorry confusing. you are right, i only have one E1 line at outbound connection. Since you said HSRP not much use for that situation, so do you have any idea how to do a redundency with 2 router and with one E1 line?

Thanks

[Richard Burts]

Seng

I suggest that you think through what you are trying to accomplish. I believe that once we get clear on what problem we are trying to solve it becomes much more easy to find an appropriate solution.

You raise the question of redundancy, so lets think a bit about redundancy. You state that you have only a single E1, so there is no redundancy for outbound traffic. You have only a single link for outbound traffic and a potential single point of failure there. Two routers running HSRP could provide redundancy for the LAN connection. It might be helpful to have HSRP if there is significant traffic from end stations to destinations in the local environment but in different subnets so it would go through the router as default gateway (what HSRP really provides is redundancy of the default gateway of the end stations). Is that the environment that you are in?

HTH

Rick

[jarathbu]

Hello,

No you can not configure a pair of FE interfaces with the same IP address. However, for redundancy, etc, you can configure HSRP, GLBP or VRRP. This will allow you to use the same "virtual IP address" but the physical addresses must be unique. Hope this helps.

Regards,

James

[Richard Burts]

James suggestions are interesting but I am not sure that they would work. In particular I believe the HSRP solution would not work since the two interfaces are on the same router. HSRP needs two interfaces in the same broadcast domain, where each interface has a unique address in the same subnet and the interfaces share a virtual address. But IOS will not allow you to configure two LAN interfaces on the same router to be in the same subnet. I have similar doubts about GLBP and VRRP.

There is one alternative which might work which is to configure Integrated Routing and Bridging. In doing this you configure both FastEthernet interfaces with bridging enabled and no IP address on the physical interface. You configure a BVI (Bridged Virtual Interface) which shares the bridge group with the interfaces and the IP address is configured on the BVI. The IOS will allow you to do this and it would allow both FastEthernet interfaces to be connected in the same broadcast domain.

I suspect that the IRB solution may be more complex than you want to get into. Perhaps if you tell us more about what you are attempting to achieve we might find other suggestions of how to achieve it.

HTH

Rick