Apply the Zone protection profile to one zone or both, depending on if asymmetric traffic is required. The duplicate ACK is typically received at the Sender in the following scenario: Receiver receives packet 1. This will normally happen if there is asymmetric routing in the network. For example, if a SYN packet goes through the Palo Alto Networks firewall, but SYN-ACK never goes through the firewall and the firewall receives an ACK. The firewall will drop the packets because of a failure in the TCP reassembly.Issue. Running tshark or dumpcap to packet capture on the loopback interface results in TCP ACKed unseen segment and TCP Previous segment not captured when run in a virtual machine.
Tcp Ack Unseen Segment Full Connections Which
The packet traverses as belowClient - firewall - ipsec tunnel - firewall - loadbalancer - serverWhen we do a TCP dump between the firewall and loadbalancer we can see the successfull connections which follows the normal 3 way handshake as expected but when we look at the failed transactions we are seeing the follwingSYN,ACK SEQ(totally random number 124124) ACK(totally random number + 1 - 124125) SYN SEQ(1000000)SYN,ACK SEQ(t124124) ACK(124125)And so on until the packet is dropped. I have been investigating an issue for a month now and still can't figure out what the issue is.Basically we have clients connecting to a server on port 80 but 1% of the connections fail due to a socket error. For more information on packet captures, see: Using Packet Filtering through GUI with PAN-OS 4.1As shown below, in the counters see that the packets are getting dropped due to TCP reassembly. Captures show it is receiving a SYN packet and an ACK packet, but never receives a SYN ACK:Use the following command to configure the firewall to bypass asymmetric routing globally.# set deviceconfig setting tcp asymmetric-path bypassThe changes can be reverted back with the following:# delete deviceconfig setting tcp asymmetric-pathUse the following command to check the current action on asymmetric traffic:> show running tcp state | match asymmetricSession with asymmetric path : drop packetAlternatively, users can narrow down bypass asymmetric routing just for traffic going to a specific destination Zone by creating a Zone Protection Profile. Go to the Packet Based Attack Protection tab and, on the pulldown menu, select the following: Go to Network > Zone Protection Profile.
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