Step 1
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show
tcp [line-number] [tcb
address]
Displays the status of TCP connections. The arguments and keyword are as follows:
line-number—(Optional) Absolute line number of the Telnet connection status.
tcb—(Optional) Transmission control block (TCB) of the Explicit Congestion Notification (ECN)-enabled connection.
address—(Optional) TCB hexadecimal address. The valid range is from 0x0 to 0xFFFFFFFF.
The following sample output from the
show
tcp
tcb command displays detailed information about an ECN-enabled connection that uses a hexadecimal address format:
Example:
Device# show tcp tcb 0x62CD2BB8
Connection state is LISTEN, I/O status: 1, unread input bytes: 0
Connection is ECN enabled
Local host: 10.10.10.1, Local port: 179
Foreign host: 10.10.10.2, Foreign port: 12000
Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)
Event Timers (current time is 0x4F31940):
Timer Starts Wakeups Next
Retrans 0 0 0x0
TimeWait 0 0 0x0
AckHold 0 0 0x0
SendWnd 0 0 0x0
KeepAlive 0 0 0x0
GiveUp 0 0 0x0
PmtuAger 0 0 0x0
DeadWait 0 0 0x0
iss: 0 snduna: 0 sndnxt: 0 sndwnd: 0
irs: 0 rcvnxt: 0 rcvwnd: 4128 delrcvwnd: 0
SRTT: 0 ms, RTTO: 2000 ms, RTV: 2000 ms, KRTT: 0 ms
minRTT: 60000 ms, maxRTT: 0 ms, ACK hold: 200 ms
Flags: passive open, higher precedence, retransmission timeout
TCB is waiting for TCP Process (67)
Datagrams (max data segment is 516 bytes):
Rcvd: 6 (out of order: 0), with data: 0, total data bytes: 0
Sent: 0 (retransmit: 0, fastretransmit: 0), with data: 0, total data
bytes: 0
Cisco Software Modularity
The following sample output from the
show
tcp
tcb command displays a Software Modularity image:
Example:
Device# show tcp tcb 0x1059C10
Connection state is ESTAB, I/O status: 0, unread input bytes: 0
Local host: 10.4.2.32, Local port: 23
Foreign host: 10.4.2.39, Foreign port: 11000
VRF table id is: 0
Current send queue size: 0 (max 65536)
Current receive queue size: 0 (max 32768) mis-ordered: 0 bytes
Event Timers (current time is 0xB9ACB9):
Timer Starts Wakeups Next(msec)
Retrans 6 0 0
SendWnd 0 0 0
TimeWait 0 0 0
AckHold 8 4 0
KeepAlive 11 0 7199992
PmtuAger 0 0 0
GiveUp 0 0 0
Throttle 0 0 0
irs: 1633857851 rcvnxt: 1633857890 rcvadv: 1633890620 rcvwnd: 32730
iss: 4231531315 snduna: 4231531392 sndnxt: 4231531392 sndwnd: 4052
sndmax: 4231531392 sndcwnd: 10220
SRTT: 84 ms, RTTO: 650 ms, RTV: 69 ms, KRTT: 0 ms
minRTT: 0 ms, maxRTT: 200 ms, ACK hold: 200 ms
Keepalive time: 7200 sec, SYN wait time: 75 sec
Giveup time: 0 ms, Retransmission retries: 0, Retransmit forever: FALSE
State flags: none
Feature flags: Nagle
Request flags: none
Window scales: rcv 0, snd 0, request rcv 0, request snd 0
Timestamp option: recent 0, recent age 0, last ACK sent 0
Datagrams (in bytes): MSS 1460, peer MSS 1460, min MSS 1460, max MSS 1460
Rcvd: 14 (out of order: 0), with data: 10, total data bytes: 38
Sent: 10 (retransmit: 0, fastretransmit: 0), with data: 5, total data bytes: 76
Header prediction hit rate: 72 %
Socket states: SS_ISCONNECTED, SS_PRIV
Read buffer flags: SB_WAIT, SB_SEL, SB_DEL_WAKEUP
Read notifications: 4
Write buffer flags: SB_DEL_WAKEUP
Write notifications: 0
Socket status: 0
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Step 2
|
show
tcp
brief [all |
numeric]
(Optional) Displays addresses in IP format.
Use the
show
tcp
brief command to display a concise description of TCP connection endpoints. Use the optional
all keyword to display the status for all endpoints with addresses in a Domain Name System (DNS) hostname format. If 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 Foreign Address (state)
609789AC Device.cisco.com.23 cider.cisco.com.3733 ESTAB
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 Local Address Foreign Address (state)
6523A4FC 10.1.25.3.11000 10.1.25.3.23 ESTAB
65239A84 10.1.25.3.23 10.1.25.3.11000 ESTAB
653FCBBC *.1723 *.* LISTEN
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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):
Example:
TCP0:ignoring second congestion in same window sndcwn - 512, snd_1st - 33884268765
TCP0:partial ACK received sndcwnd:338842495
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Step 4
|
debug
ip
tcp
congestion
Use the
debug
ip
tcp
congestion command to display information about TCP congestion events. The TCP/IP network isolated above the data link layer might encounter performance issues. The
debug
ip
tcp
congestion command can be used to debug these performance issues. The command also displays information related to variations in the TCP send window, congestion window, and congestion threshold window.
The following is sample output from the
debug
ip
tcp
congestion command:
Example:
Device# debug ip tcp congestion
*May 20 22:49:49.091: Setting New Reno as congestion control algorithm
*May 22 05:21:47.281: Advance cwnd by 12
*May 22 05:21:47.281: TCP85FD0C10: sndcwnd: 1472
*May 22 05:21:47.285: Advance cwnd by 3
*May 22 05:21:47.285: TCP85FD0C10: sndcwnd: 1475
*May 22 05:21:47.285: Advance cwnd by 3
*May 22 05:21:47.285: TCP85FD0C10: sndcwnd: 1478
*May 22 05:21:47.285: Advance cwnd by 9
*May 22 05:21:47.285: TCP85FD0C10: sndcwnd: 1487
*May 20 22:50:32.559: [New Reno] sndcwnd: 8388480 ssthresh: 65535 snd_mark: 232322
*May 20 22:50:32.559: 10.168.10.10:42416 <---> 10.168.30.11:49100 congestion window changes
*May 20 22:50:32.559: cwnd from 8388480 to 2514841, ssthresh from 65535 to 2514841
For Cisco TCP, New Reno is the default congestion control algorithm. However, an application can also use Binary Increase Congestion Control (BIC) as the congestion control algorithm. The following is sample output from the
debug
ip
tcp
congestion command using BIC:
Example:
Device# debug ip tcp congestion
*May 22 05:21:42.281: Setting BIC as congestion control algorithm
*May 22 05:21:47.281: Advance cwnd by 12
*May 22 05:21:47.281: TCP85FD0C10: sndcwnd: 1472
*May 22 05:21:47.285: Advance cwnd by 3
*May 22 05:21:47.285: TCP85FD0C10: sndcwnd: 1475
*May 22 05:21:47.285: Advance cwnd by 3
*May 22 05:21:47.285: TCP85FD0C10: sndcwnd: 1478
*May 22 05:21:47.285: Advance cwnd by 9
*May 22 05:21:47.285: TCP85FD0C10: sndcwnd: 1487
*May 20 22:50:32.559: [BIC] sndcwnd: 8388480 ssthresh: 65535 bic_last_max_cwnd: 0 last_cwnd: 8388480
*May 20 22:50:32.559: 10.168.10.10:42416 <---> 10.168.30.11:49100 congestion window changes
*May 20 22:50:32.559: cwnd from 8388480 to 2514841, ssthresh from 65535 to 2514841
*May 20 22:50:32.559: bic_last_max_cwnd changes from 0 to 8388480
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