Stretch VLANs & network across 3 sites with P2P links

[Peter Thomas]

Looking for advice on the following:

Primary site with WAN connectivity to all offices through 3rd party WAN provider.

Backup site has failover WAN connectivity to all offices through 3rd party WAN provider.

100MB P2P link in place between primary & backup site.

VLAN & network currently stretched across two sites.

Need to open a new office and looking to see best method to stretch existing vlans across this new office. New office will have 100MB link to primary and another 100M P2P to backup site.

Collapsed core at primary is stack of 3850, collapsed core at backup is stack of 3850.

Considering the risk of broadcast storm, split-horizon and complex routing, what is the recommended approach to this design.

[Dennis Mink]

I would think talk to your provider that has already offered you the layer 2 link and get an additional layer 2 link to your new office.

my question would be, do you really need that layer 2 link. normally you would see layer 2 links between core sites i.e. redundant datacentres?

[paul driver]

Hello

personally I wouldn’t go for a L2 extended design as you would need rely on stp to negated loops - which could be negated by a L3 design approach.

However if you need to extended by L2 then obviously apply latest stp (802.1w - rpvst+). prune off any vlans not require to traverse the trunks interconnects and apply L2 port security.

Have the trunks to either core stack aggregated for extra resiliency