There is a way to firewall traffic within the same IP subnet but your firewall needs to be in transparent mode. However I am not suggesting you do this as I suspect you have other interfaces on your ASA in use and your ASA is in routed mode.
In which case no you cannot use the firewall as far as I know because traffic is never sent to the firewall ie. the traffic goes direct between clients in the same subnet.
Which means you could use another vlan although this would mean readdressing etc. or alternatively your switch may be able to filter traffic within the same vlan depending on the model. Bear in mind this is not stateful firewalling just basic acl filtering.
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...