Cisco ASR 1000 Series Configuration Manual page 43

Configuring TCP
this keyword is not used, endpoints in the LISTEN state are not shown. Use the optional numeric keyword to display
the status for all endpoints with addresses in IP format.
Note If the ip domain-lookup command is enabled on the device, and you execute the show tcp brief command,
the response time of the device to display the output will be very slow. To get a faster response, you should
disable the ip domain-lookup command.
The following is sample output from the show tcp brief command while a user is connected to the system by using
Telnet:
Example:
Device# show tcp brief
TCB Local Address
609789AC Device.cisco.com.23
The following example shows the IP activity after the numeric keyword is used to display addresses in IP format:
Example:
Device# show tcp brief numeric
TCB
6523A4FC
65239A84
653FCBBC
Step 3
debug ip tcp transactions
Use the debug ip tcp transactions command to display information about significant TCP transactions such as state
changes, retransmissions, and duplicate packets. The TCP/IP network isolated above the data link layer might encounter
performance issues. The debug ip tcp transactions command can be useful in debugging these performance issues.
The following is sample output from the debug ip tcp transactions command:
Example:
Device# debug ip tcp transactions
TCP: sending SYN, seq 168108, ack 88655553
TCP0: Connection to 10.9.0.13:22530, advertising MSS 966
TCP0: state was LISTEN -> SYNRCVD [23 -> 10.9.0.13(22530)]
TCP0: state was SYNSENT -> SYNRCVD [23 -> 10.9.0.13(22530)]
TCP0: Connection to 10.9.0.13:22530, received MSS 956
TCP0: restart retransmission in 5996
TCP0: state was SYNRCVD -> ESTAB [23 -> 10.9.0.13(22530)]
TCP2: restart retransmission in 10689
TCP2: restart retransmission in 10641
TCP2: restart retransmission in 10633
TCP2: restart retransmission in 13384 -> 10.0.0.13(16151)]
TCP0: restart retransmission in 5996 [23 -> 10.0.0.13(16151)]
The following line from the debug ip tcp transactions command sample output shows that TCP has entered Fast
Recovery mode:
Example:
fast re-transmit - sndcwnd - 512, snd_last - 33884268765
The following lines from the debug ip tcp transactions command sample output show that a duplicate acknowledgment
is received when TCP is in Fast Recovery mode (first line) and a partial acknowledgment has been received (second
line):
Foreign Address
cider.cisco.com.3733
Local Address Foreign Address
10.1.25.3.11000 10.1.25.3.23
10.1.25.3.23 10.1.25.3.11000
*.1723 *.* LISTEN
IP Application Services Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 1000)
Verifying TCP Performance Parameters
(state)
ESTAB
(state)
ESTAB
ESTAB
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