Sudden connection failures in TCP traffic such as SSH, NFS, CIFS with Cisco ASA firewall

Solution Unverified - Updated -


  • After a Cisco ASA firmware upgrade, connections are dropped. The Cisco ASA reports a TCP PAWS failure and drops packets:
33: 19:10:43.774236       802.1Q vlan#123 P0 > P 299327905:299328005(100) ack 207669419 win 339 <nop,nop,timestamp 2703 2363294310> Drop-reason: (tcp-paws-fail) TCP packet failed PAWS test
  • TCP sessions like SSH appear to hang, but establishing a new session works again straight away
  • NFS Client reports "nfs: server not responding" then "nfs: server OK" 10 minutes later


  • Red Hat Enterprise Linux
  • Cisco ASA, seen on firmware versions 9.6(2) or 9.1(7)9
  • TCP connection. More likely with long-lived TCP connection such as SSH, NFS, CIFS, etc

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