On the WAN side I do not see any issues as you will send all internet traffic over one router and then the connections to the other Sites via another router. PBR is not supported on the ASA but you will be able to accomplish this particular scenario
Now on the LAN side , the ASA 5520 needs to have each interface attached to a differnet subnet, in this case you will have two interface going to 2 different switches on the same subnet witch you cannot do it. I think what you could do is to have redundant interfaces.
You cannot use 2 interfaces at the same time connecting to the same subnet ( unless firewall is on transparent mode), so what you can do on this case will be to use redundant interfaces ( one will be up, the other one will be on stand-by) so you will provide more redundancy to your network witch I think is what you are looking for.
Julio Carvajal Senior Network Security and Core Specialist CCIE #42930, 2xCCNP, JNCIP-SEC
1-So basically the two routers are on the same broadcast domain than the ASA, the thing is that as soon as you remove the layer two switch you will need to use a separate interface to connect to each router, so then each interface will need to be on a different subnet ( let me know if that is possible).
2- So if you can set up that scenario ( 2 subnets) as you know the ASA does not support PBR but as you know the destination for the customer´s branchs we can do configure this:
Login to the FXOS chassis manager.
Direct your browser to https://hostname/, and log-in using the user-name and password.
Go to Help > About and check the current version:
Check the current version availa...
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...