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Spanning VLAN's


I would like to know if anyone has come across my situation before, our server guys want to have primary and backup servers on the same IP subnet which are located in our local site and DR site across a WAN connection.

In the past I have rejected this request as I do not want to span VLAN's over the WAN connection for obvious layer 2 issues that can arise and have suggested that they use DNS.

Could anyone sugest a solution to this problem if DNS cannot be used but the primary and secondary devices must be on the same IP Subnet.



Re: Spanning VLAN's

You were quite right in refusing to implement this. Using the WAN for layer2 ethernet is only possible when you have an ethernet-type of wan link with ethernet speed.

Nowadays this kind of links are becoming more and more available and your company might posess one as well but still there is likely to be a mismatch in speed while the latency, packet loss and overbooking on the wan must be taken into account as well.

My personal opinion is that a good server design should not require this type of measures to be taken in the infrastructure.

Be warned that they will know where to find you once they are running into troubles with the link.

Now, I have built a design like above using a dual fiber ring with gigabit ethernet and 6500 series switches. This worked but proved once more that a redundant layer2 design will always have the issues that are related to spanning tree.

Using a Layer3 design is really the preferrable solution.



New Member

Re: Spanning VLAN's

um you can lookinto IRB feature of IOS - so you can populate your VLANs from one facility to another ... i believe there is something more newer than IRB (as IRB has some can google on cisco's website)

second option will be EoMPLS (Ethernet over MPLS)

and third option (which i have only herd - not used) is Anycast routing :)

if you go through anycast techniques (manipulate it apporpriately according to your scenario)

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