There is no reason why the 2 (GLBP + A/S on FWSM) can't co-exist. They are independent of each other.
MSFC would forward traffic over your L2 trunk between your 6500 chassis to the active firewall. Which answers your next question - yes you do need L2 trunk for the FWSM vlans for 2 reasons
1) For forwarding traffic as described above
2) For failover between the FWSM modules.
You could run GLBP on vlan 100 but you wouldn't get any benefit because the source mac-address will always be the active FWSM and this is the only sender on that vlan so there are no other senders to load balance across both MSFCs.
No you don't have to trunk all the user vlans, apologies if i gave that impression. But you do need to trunk vlan 100 so that if the MSFC that is acting as the default-gateway on the clients is on the other 6500 from the FWSM active gateway it can stil send traffic to the active FWSM.
You do have a L2 trunk on your diagram unless i am misunderstanding - the one for the FWSM vlans ?
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...