Dropping packets with UDP port 0 is normal behaviour because firewall products treat this as a security violation, and drop the packet. You may try to configure the traffic to use some other port or you may permit the UDP port 0 by applying an access-list.
Something like that happen to me in the past with OS 6.X with a Solaris box. When users try to established an Exceed session the PIX block the traffic. The X Windows use ports 0 and 1 for the displays. I had to call the TAC and it took 2 days to figure it out. The command that fix the problem was the established.
established command?This command allows return connections from a lower security host to a higher security host if there is already an established connection from the higher level host to the lower level host.
For same security interfaces, you can configure established commands for both directions.
This was the command I used:
established tcp 0 6000 permitto tcp 6000 permitfrom tcp 1024-65535
Still I don't know if it will resolve your issue because your traffic it's UDP.
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...