I've experienced a few issues with enabling anti-spoofing through the unicast reverse path forwarding feature on ASAs.
The version in question is 9.1.3 on an HA pair of ASA5550's.
When enabling this through the commands: ip verify reverse-path interfaceinterface_name it seemed to cause a couple of issues:
(it was enabled on all interfaces to begin with)
1. The first issue was that all outbound traffic was dropped altogether.
2. The second issue was that for connected remote access VPN clients, they were able to connect fine but subsequent outbound internet connectivity was unavailable until this page was refreshed several times. This issue went away as soon as this feature was removed.
I know that unicast reverse path forwarding typically should only uncover problems with the flow of network due to diverse routing etc. but I was wondering whether anyone has uncovered any strangle anomolies when implementing this.
For outside traffic, for example, the ASA can use the default route to satisfy Unicast RPF protection. If traffic enters from an outside interface, and the source address is not known to the routing table, the ASA uses the default route to correctly identify the outside interface as the source interface.
Thanks so much for your replies. It turned out that there was neither diverse/asymmetric routing in place but the drops were all packets that should have been dropped such as broadcasts. We never got to the bottom of the VPN anomaly as it seemed to resolve itself but that seemed to be AV linked.
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...