Name: Cisco ASR 1000 Series
Brand: Cisco
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Configuration Examples for TCP

Example: Verifying the Configuration of TCP ECN

The following example shows how to verify whether TCP ECN is configured:

Device# show running-config

Building configuration...

ip tcp ecn ! ECN is configured.

The following example shows how to verify whether TCP is ECN-enabled on a specific connection (local

host):

Device# show tcp tcb 123456A

!Local host

Connection state is ESTAB, I/O status: 1, unread input bytes: 0

Connection is ECN Enabled

Local host: 10.1.25.31, Local port: 11002

Foreign host: 10.1.25.34, Foreign port: 23

The following example shows how to display concise information about one address:

Device# show tcp brief

TCB Local address Foreign Address (state)

609789C Router.example.com.23 cider.example.com.3733 ESTAB

The following example shows how to enable IP TCP ECN debugging:

Device# debug ip tcp ecn

TCP ECN debugging is on

Device# telnet 10.1.25.31

Trying 10.1.25.31 ...

01:43:19: 10.1.25.35:11000 <---> 10.1.25.31:23 out ECN-setup SYN

01:43:21: 10.1.25.35:11000 <---> 10.1.25.31:23 congestion window changes

01:43:21: cwnd from 1460 to 1460, ssthresh from 65535 to 2920

01:43:21: 10.1.25.35:11000 <---> 10.1.25.31:23 in non-ECN-setup SYN-ACK

Before a TCP connection can use ECN, a host sends an ECN-setup SYN (synchronization) packet to a remote

end that contains an Echo Congestion Experience (ECE) and Congestion window reduced (CWR) bit set in

the header. Setting the ECE and CWR bits indicates to the remote end that the sending TCP is ECN capable,

rather than an indication of congestion. The remote end sends an ECN-setup SYN-ACK (acknowledgment)

packet to the sending host.

In this example the “out ECN-setup SYN” text means that a SYN packet with the ECE and CWR bit set was

sent to the remote end. The “in non-ECN-setup SYN-ACK” text means that the remote end did not favorably

acknowledge the ECN request and, therefore, the session is not ECN capable.

IP Application Services Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 1000)

Configuring TCP

Configuration Examples for TCP

Cisco ASR 1000 Series Configuration Guide

Other manuals for Cisco ASR 1000 Series