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New Member

Bridging Across serial interfaces...same subnet on both ends

I have two routers connected via 64K serial interfaces....The ip address on the ethernet of both routers is in the same subnet....My questions is..>Can I bridge like subnets across those serial interfaces...I need to maintain IP integrity at both ends for management purposes...perhaps a tunnel...I just don't know..can't remember...

9 REPLIES
Hall of Fame Super Silver

Re: Bridging Across serial interfaces...same subnet on both ends

Hello,

you need to use IRB and bridging over the serial interfaces

int eth0

no ip address

bridge-group 1

int ser0/0

ip addr

bridge-group 1

int bv1

! here the shared subnet

ip address x.x.x.1 255.255.255.0

bridge 1 protocol ieee

bridge 1 route ip

do it on both ends/routers

Hope to help

Giuseppe

New Member

Re: Bridging Across serial interfaces...same subnet on both ends

Do the serial interfaces need a 30 bit IP range to connect them///or no ip address on the serial

Hall of Fame Super Silver

Re: Bridging Across serial interfaces...same subnet on both ends

Hello,

you should be fine with no ip address on the serial interfaces.

I've noticed that you say you have only 64kbps link so a bridging solution is probably troublesome:

broadcast traffic is enough to saturate the link if this is a real production network and not a lab.

Hope to help

Giuseppe

New Member

Re: Bridging Across serial interfaces...same subnet on both ends

The bandwidth is small but, the application is tiny..just polling a RTU...once evrey 5 minutes...the whole network is for that...thanks again

Hall of Fame Super Bronze

Re: Bridging Across serial interfaces...same subnet on both ends

Once you configure bridging, the WAN won't be used just for that small application transfer but every single broadcast in either side of the network will traverse that link.

In a LAN segment, broadcast traffic is barely a problem since you usually have a LAN with speeds of 10Mbps or better.

With this design, your LAN speed will be as low as 64kbps depending on the switch/router root placement.

I strongly suggest to revisit this design.

__

Edison.

Hall of Fame Super Bronze

Re: Bridging Across serial interfaces...same subnet on both ends

Be aware that extending your Layer2 topology over slow unreliable WAN links will create atrocious performance issues in the network at both ends of the link.

I suggest re-examining your network and provide a Layer3 design that fulfills this need without going the bridging path.

HTH,

__

Edison.

Hall of Fame Super Blue

Re: Bridging Across serial interfaces...same subnet on both ends

Edison

Off the top of your head do you know if L2TPv3 is any better in terms of performance across a WAN link ?

Jon

Hall of Fame Super Bronze

Re: Bridging Across serial interfaces...same subnet on both ends

Jon,

They both accomplish the same thing, i.e. extending a L2 topology.

With that said, L2TPv3 is mostly used to accommodate customers on a point-to-point virtual connection.

For instance, a service provider would use 2 routers with L3 inter-connectivity and assign a L2 port for each CE. The CEs, in turn, will be able to create L3 point-to-point connection, pretty much like your typical point-to-point serial link. In this case, that's a proper use of L2TPv3 implementation.

__

Edison.

Hall of Fame Super Bronze

Re: Bridging Across serial interfaces...same subnet on both ends

Jon,

Another thing just came to my head :)

When you enable bridging between 2 routers, say a service provider doing what I mentioned before, you are automatically enabling spanning-tree and a root election will take place. This add some overhead over WAN links.

While, when you enable L2TPv3, you are creating a pseudowire for devices that are attached 'xconnect' interfaces. No spanning-tree is running on the service provider devices - hence it is much cleaner solution.

__

Edison.

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