We have equipment stored in two data centres. Currently we have a layer 2 network that spans both centres. This layer 2 network is provided to us by our ISP and they also run transit on top, a single IP range that also spans both centres. This forms essentially an active/active connection
Both sites have the same default gateway
This means I can use
a.b.c.1/24 on site A a.b.c.2/24 on site B
and if I have any issues on site A I can move a.b.c.1/24 to a device on site B and everything carries on working ok.
I don't know 100% what our provider uses to achieve this apart from a VRRP instance to provide some resilience for gateway address.
Now I am looking to install an exact copy of this setup as a backup connection. For now all I wanted was for another provider to do exactly the same thing just with a different IP range (we don't have a PI range).
This time round I have been told that the only way this can be done is if we establish a BGP peering session to them (the backup provider) and advertise the (new) IP addresses we are using at each site back to them.
To me this didn't sound right but then I haven't done a lot of work with BGP. Is it possible that you can advertise the same IP range to a single ISP from two different sites and be able to achieve what I described above?