Bridging Ethernet to WAN

[provis]

1. Is it possible to bridge an ethernet port to and E1 WAn port on a cisco

router.

2. How Can it be done.

ethernetport<router1>WANport------leasedline------WANport<router2>Ethernet

What are the cisco router that supports this configuration and what are the basic bridging commands to be used ?

Thanks.

[vcjones]

You are looking for standard remote transparent bridging, which is available on virtually all Cisco routers, although it may not be on the very small SOHO routers like the 800 series. There are many example configurations here on CCO, try searching for "bridge group" one of the commands required which will be in all the example configurations.

The far more critical question you need to ask yourself is "Do you really want to bridge?" Remote bridging is problematic in terms of performance and rarely useful on any WAN link slower than T1, and many applications have significant performance problems even at that data rate because they assume negligable delivery delays on individual packets. Catch-22 is that it is usually the applications which are most prone to performance problems which are forcing you to use remote bridging in the first place.

Good luck and have fun, and if you're technically inclined, read the white paper "Performance Impact of Backbone Speed in Switched Backbone Architectures" on my web site and substitute your WAN for the LAN backbone in the analysis.

Vincent C Jones

www.networkingunlimited.com

[provis]

The purpuse i'm bridging is to pass vlan tags through the two links.

Is there any other way beside bridging that i could do it over an E1 WAN link?

The only other way that i could think of is to pull a direct fiber to connect the two LANs.

Thanks for your reply :)

[lgijssel]

When you install a fiber link it will be very well possible to connect the two sites by means of a vlan-trunk. If you need to use the E1 connection, you will be better off (performancewise) when you use the E1 as a routed connection.

You will need to establish two distinct vtp-domains and correct routing between the sites. This will perform much better because of:

- smaller datagrams are sent over the link, with briding L2 is included

- no background broadcast traffic on the E1, but a lot of it when bridiging.

Regards,

Leo

[bbravo]

Are you also aware of utilization issues when bridging over a DS3? for instance I'm having an issue with my DS3 link, it seems (through Ciscoworks) that only 40 % gets used no matter how many file transfer and file sizes go across the link, thanks for your time.

[vcjones]

Two possibilities come to mind:

1 - Does the bandwidth parameter configured on the interface match the actual bandwidth of the link? (See what "show interface" says the bandwidth is).

2 - The DS3 introduces delay, which can have a major impact on throughput if the TCP window size is not large enough. Hint: Windows default window size (RWIN) is not large enough for a DS3.

Good luck and good hunting!

Vincent C Jones