Link Controller, dual-homing with two ISP and own ASN and IP blocks
I've been reading and searching around to find an answer to my question but there is one part that is not clear.
We have a data center with our own /21 IP block and ASN. Currently we are connected through an ISP and have a pair of BIG-IP Link controllers in HA connected to a pair of Cisco routers which are then connected to the service provider. Inbound traffic goes through a Firewall before entering the network.
It is not possible to provide IP-transit, so BGP is out of the question.
We want to have a second ISP as backup link so we can have failover in case the main link goes down.
Everything I read around the Internet speak about how to configure the links and how the device manages links and can load balance. I understand the scenarios where we should have two separate VLANs for connections to ISPs, and virtual servers and pools.
But the question is, knowing that we have our IP block that should be advertised by the ISP for global routing, how is that managed in case a second ISP enters the game, since they should both advertise the routes towards the data center, what happens if one link goes down?
Does this setup require the ISPs to cooperate with us and perhaps stop advertising if one link goes down, thus the setup is no longer transparent to the ISPs?
Also, when having both links up and running, with both ISPs advertising, does this mean response packets can come back through the other link? and does the BIG-IP handle that?
Or it is not possible to have the entire range advertised by both and we should be splitting the range and have each service presented with two virtual servers, one for each link?