Thursday, 9 May 2013

Understanding TCP connection flags

Cisco ASA Firewall  TCP Connection Flags.
 When troubleshooting TCP connections through the ASA, the connection flags shown for each TCP

connection provide a wealth of information about the state of TCP connections to the ASA. This information can be used to troubleshoot problems with the ASA, as well as problems elsewhere in the network.

Here is the output of the show conn protocol tcp command, which shows the state of all TCP connections through the ASA. These connections can also be seen with the show conn command.

ASA# show conn protocol tcp
101 in use, 5589 most used
TCP outside 10.23.232.59:5223 inside 192.168.1.3:52419, idle 0:00:11, bytes 0, flags saA
TCP outside 192.168.3.5:80 dmz 172.16.103.221:57646, idle 0:00:29, bytes 2176, flags UIO
TCP outside 10.23.232.217:5223 inside 192.168.1.3:52425, idle 0:00:10, bytes 0, flags saA
TCP outside 10.23.232.217:443 inside 192.168.1.3:52427, idle 0:01:02, bytes 4504, flags UIO
TCP outside 10.23.232.57:5223 inside 192.168.1.3:52412, idle 0:00:23, bytes 0, flags saA
TCP outside 10.23.232.116:5223 inside 192.168.1.3:52408, idle 0:00:23, bytes 0, flags saA
TCP outside 10.23.232.60:5223 inside 192.168.1.3:52413, idle 0:00:23, bytes 0, flags saA
TCP outside 10.23.232.96:5223 inside 192.168.1.3:52421, idle 0:00:11, bytes 0, flags saA
TCP outside 10.23.232.190:5223 inside 192.168.1.3:52424, idle 0:00:10, bytes 0, flags saA



The next picture shows the ASA TCP Connection flags at different stages of the TCP state machine. The
connection flags can be seen with the show conn command on the ASA.
 


TCP Connection Flag Values
   
Additionally, in order to view all of the possible connection flags issue the show connection detail command
on the command line:
ASA# show conn detail
84 in use, 1537 most used
Flags: A − awaiting inside ACK to SYN, a − awaiting outside ACK to SYN,
B − initial SYN from outside, b − TCP state−bypass or nailed, C − CTIQBE media,
D − DNS, d − dump, E − outside back connection, F − outside FIN, f − inside FIN,
G − group, g − MGCP, H − H.323, h − H.225.0, I − inbound data,
i − incomplete, J − GTP, j − GTP data, K − GTP t3−response
k − Skinny media, M − SMTP data, m − SIP media, n − GUP
O − outbound data, P − inside back connection, p − Phone−proxy TFTP connection,
q − SQL*Net data, R − outside acknowledged FIN,
R − UDP SUNRPC, r − inside acknowledged FIN, S − awaiting inside SYN,
s − awaiting outside SYN, T − SIP, t − SIP transient, U − up,
V − VPN orphan, W − WAAS,
X − inspected by service module

 



No comments:

Post a Comment