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Conserve VLAN tagging over a 7204 with one ATM PVC


we want to move our DataCenter and want to bridge our networks during the move between the two locations. The routers are 7204 and the Switches in both locations 6509/6006/4006.

Is it possible to conserve multiple VLANs through one ATM PVC in bridging mode on the 7204?



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Re: Conserve VLAN tagging over a 7204 with one ATM PVC

Hi Traugott,

The trick here is to preserve the "tag" {VLAN ID} across the ATM WAN. You will need to establish VLAN trunk connections between the switches and 7204 routers via either using ISL or 802.1q encapsulation. From what I have read, the "tag" is stripped from the frame on the router's ingress port. Remember ISL / 802.1q trunking is "truely" point-to-point! There are two possible solutions to this:

1) Test Transparent Bridging between the router's trunk port and the ATM interface (ie every frame received on the trunk port is "bridged" across to the ATM PVC) - and likewise the frame is delivered to the other end with the "tag" field still preserved.

2) On the router configure for 802.1q Tunnelling - this is a SP feature which allows the transport of multiple VLANs across a WAN (ie SP network) using only 1 VLAN - ie the original tag field is not stripped, but rather an additional tag is added at the 802.1q tunnel ingress point and later stripped at the tunnel egress point. (You can search CCO for info on this)

The cavaet is that the 7200 platform does not support 802.1q trunking nor the 802.1q tunnel feature. Suggest to look at perhaps the 3600 router as you can get ATM modules for it and it supports all the 802.1q functionality. Come to think of it the 7600 platform supports this functionality.(IP PLUS image).


BTW - I'm also relocation a Data Centre and will shortly perform POC testing with the above - when I obtain some additional DRAM etc :-)

Good Luck

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