Bridged router interfaces and OSPF

[Jesse Hottle]

Hello,

Is it possible to bridge two interfaces together and run OSPF between on each interface? Example: We have a remote site with two connections to a central location. We would like to share the bandwidth of both connections between the two locations, while also having a backup in case one of the connections fails.

Each site has a router.

Any help would be appreciated.

[paolo bevilacqua]

Hi, you don't need to use bridging to share bandwidth. Configure OSPF for the physical interfaces, and it will share traffic nicely. That is what routing is designed for.

[Jesse Hottle]

lol. I agree.

What I have is two 30mb links. If we bridge the two interfaces, we affectively get close to 60mb aggregate. At this central locations we are also running other instances of osfp on our backbone network.

All I am asking is if this is possible and what are the plus/minuses for such a configuration.

[paolo bevilacqua]

Hi, when you bridge over parallel links, one link will shut down due to STP, and that is understandable, as bridging has no load sharing mechanism.

If you're looking for single-session speeds of more that 30 mb in your case, that is not possible to do with ethernet, sorry.

Else, both an etherchannel/PAgP or routing based load sharing configuration would use both circuits equally on a statistical basis.

[Jesse Hottle]

Is this just a "Cisco" thing? Because I can do this using a MikroTik, StarOS, or ImageStream routers. Our site to site links are wireless backhauls.

Here is an example:

Site A:

Int1

description Link A

10.1.0.1/30

opsf point-to-point

bridge1

Int2

description Link B

10.2.0.1/30

ospf point-to-point

bridge1

Site B:

Int1

description Link A

10.1.0.2/30

ospf point-to-point

bridge2

Int2

description Link B

10.2.0.2/30

ospf point-to-point

bridge2

ospf

network 10.1.0.0/30

network 10.2.0.0/30

One thing we have been doing is we bridge both Int1 and Int2 on each router. Each interface is seperate within our OSPF configuration. If we keep the cost the same for both links, we are able to use the full combined throughput of both wireless backhauls. If we change the cost on one of the links, this give us a failover link. We run router to router tcp throughput tests, and we see total throughput of close to 60mbps.

I guess I am looking for a way to do this with Cisco, as this is my own personal perference.

[Jesse Hottle]

Need clarify this, were seeing 60mbps aggregate throughput. So one backhaul in maxing at 30mb TX, and the other maxing at 30mb RX

[paolo bevilacqua]

There is no way to do with cisco, beside configuring per-packet load sharing. Since that can lead to out of order packet arrival, a bad thing, it is recommended not to be done, then again each one does what he wants with his own equipment.