1. Is NAT a condition to use multiple context with shared outside interface
2. Can IDSM be deployed to FWSM in multiple context. I believe If I failover single FWSM context to redundant Cat6500 chassis, IDSM will not work because IDSM can be active against one physical FWSM only.
1) That's a very good question. When you share a vlan between contexts then the FWSM classifier comes into play. You need to have a read of this section. Sharing the same vlan for outside contexts is the most common approach so it is less problematic -
If you have any more questions on this please come back.
2) Unfortunately can't really help you on this as i have no real experience with the IDSM. I have used CSM-S modules (load-balancers) in conjunction with the FWSM's and they work in failover mode but i wouldn't want to say if this is possible with the IDSM.
In my case all the NAT'ing is done on perimeter firewall and not FWSM. Traffic from firewall is routed to MSFC and then FWSM. So there is a single outside interface on FWSM, where the destination IP is already NAT'ed and should belong to one of the contexts (unique IP address). My understanding is that classifier would 'not' be required in the above scenario. Please advise.
You say there is a single outside interface on FWSM but we were talking about multiple contexts using the same vlan for outside interfaces ?
Assuming you are talking about a single context then note this from the link i sent -
"Because the classifier relies on active NAT sessions to classify the destination addresses to a context, the classifier is limited by how you can configure NAT. If you do not want to perform NAT, you must use unique interfaces."
So you need NAT but all this means is you need to setup static translations ie. you don't need to actually change the IP address eg.
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...
[toc:faq]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 and UDP are I...