Layer 2 bridge over WAN

[Brunhuber Adrian]

Hi,i`m running in a problem.

I have to find a solution to migrate a subnet from site A to site B without changing the adressing.

The sites are 10km away and i dont have the posibility to go MPLS or dark fiber.

I`m thinking of implementing l2tpv3.What do you think ? This tehnology is stable ? Have you seen it somewhere in production ?

What models or routers support this feature ?

Thanks.

[Giuseppe Larosa · Accepted solution]

Hello Adrian,

L2TPv3 can be used also on SW routers like ISR 2800 series with appropriate image feature.

as a temporary fix until you move all users to the other site it may be the right tool

You understand that the amount of broadcast and multicast traffic over the involved Vlan has to be as low as possible or you will end up using all the access links or loading too much the involved routers.

Another possible solution could be NAT to be used until all hosts are migrated to the new site, this would allow better control over the level of broadcast multicast traffic but it can break some applications if ip addresses are hard coded in code.

This is important when hosts are servers that are currently interacting on a common IP subnet

Hope to help
Giuseppe

[Brunhuber Adrian]

Thanks for your quick answer.You are right,i have to control the broadcast traffic so it will not eat all my bandwidth.A few years ago when studying for CCNP i saw a scenario who used nat for this kind of situation,but i cannot see how nat can be used here ? Where do you implement nat translation in this scenario ?

[Giuseppe Larosa · Accepted solution]

Hello Adrian,

NAT could be implemented on new site to make the just moved hosts to appear to outside world as coming from a different non ambiguos subnet, or it can be done on the old site.

The issue is that for servers you may need to update DNS entries two times:

one during migration to map the moved server to the NATTED address

one at the end of migration  to restore the original entry after NAT will be removed as not needed anymore.

Hope to help

Giuseppe

[Brunhuber Adrian]

I think i will go with the l2tpv3 as a termporary solution till i`ll move all the hosts to the new site.

I the scenario for the disaster recovery if i only transport to the other site the vlan of servers (10-15 servers) so the brodcast

is at minimum do you think it will work ? I this solution only for some low incredental backups and in the case of failure users on site A to be able to authenticate in the AD on the disaster recovery site working in "emergency state" until the primary servers are up and running.

[Giuseppe Larosa · Accepted solution]

Hello Adrian,

if there are only 10-15 servers exchanging traffic over incremental backups and no multicast the only broadcast traffic is reduced to few ARP requests every X hours in the worst case  and you should be fine

Hope to help

Giuseppe