Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide 8.x
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Your software release might not support all the features documented in this module. For the latest caveats and feature information,
see the Bug Search Tool at https://tools.cisco.com/bugsearch/ and the release notes for your software release. To find information about the features documented in this module, and to
see a list of the releases in which each feature is supported, see the "New and Changed Information"chapter or the Feature
History table in this chapter.
Feature History for IP TCP MSS
Table 1. Feature History for IP TCP MSS
Feature Name
Release
Feature Information
IP TCP MSS
8.2(1)
The IP TCP Maximum Segment Size (MSS) feature enables a switch to set a maximum segment size for all the TCP connections that
originate from or terminate at a Cisco Nexus 7000 Series Switch.
Information About IP TCP MSS
The IP TCP Maximum Segment Size (MSS) feature enables a switch to set a maximum segment size for all TCP connections that
originate or terminate at a Cisco Nexus 7000 Series switch. The MSS in a TCP header field is the maximum data size or payload
that a host can send or receive in a single segment. By default, a Cisco Nexus 7000 Series switch sets the MSS value to 536
bytes for IPv4 TCP connections and 1240 bytes for IPv6 TCP connections. This default value is set by the switch during the
initial TCP connection establishment.
The following figure shows how the MSS value is set between two switches for IPv4 TCP connections:
The ip tcp mss<2000> command is used on Host A to set the MSS to 2000 bytes. The difference between the route interface MTU (1500 bytes) and the
protocol header (40 bytes) is 1460 bytes.
Note
For IPv6 TCP connections, the difference between the route interface MTU (1500 bytes) and the protocol header (60 bytes) is
1440 bytes.
The switch from which the TCP connection originates will always set the MSS to the user-configured MSS or the difference between
the route interface MTU and the protocol header, whichever is lower. Thus, Host A sends a SYN packet with the proposed MSS
of 1460 bytes to Host B. After receiving the SYN packet with the proposed MSS, Host B sends a SYN-ACK packet to Host A, accepting
the proposed MSS value for the TCP connection. Host A sends an ACK packet to Host B, setting the MSS value to 1460 for the
TCP connection.
Default Settings for IP TCP MSS
Parameter
Default Setting
IP TCP MSS
536 bytes for IPv4 TCP connections
1240 bytes for IPv6 TCP connections
Guidelines and Limitations for IP TCP MSS
If the MSS has to be set to a value that is more than 1460 bytes for IPv4 TCP connections, the corresponding MTU value should
be set to the required MSS value plus 40 bytes. If the MSS has to be set to a value that is more than 1440 bytes for IPv6
TCP connections, the corresponding MTU value should be set to the required MSS value plus 60 bytes.
Configuring IP TCP MSS
Setting the MSS for TCP Connections
Procedure
Step 1
Enter global configuration mode:
switch# configure terminal
Step 2
Set a maximum segment size:
switch(config)# ip tcp mss<bytes>
Note
The IP TCP MSS range is from 68 to 10000 bytes.
Step 3
(Optional) Display the configured IP TCP MSS:
switch# show ip tcp mss
Example: Running Configuration
This example shows a running configuration, followed by a verification command that displays the configured IP TCP MSS:
configure terminal
ip tcp mss 5000
Setting TCP MSS to 5000 bytes
switch# show ip tcp mss
TCP MSS value 5000 bytes
Removing a Set IP TCP MSS
Procedure
Step 1
Enter global configuration mode:
switch# configure terminal
Step 2
Remove the configured IP TCP MSS and set the IP TCP MSS to default values:
switch(config)# no ip tcp mss
Step 3
(Optional) Display the configured IP TCP MSS:
switch# show ip tcp mss
Example: Running Configuration
This example shows a running configuration, followed by a verification command that displays the configured IP TCP MSS:
configure terminal
no ip tcp mss 5000
Setting default MSS value is 536 bytes
switch# show ip tcp mss
TCP MSS value 536 bytes
Configuration Examples for IP TCP MSS
Example: Setting the MSS for TCP Connections
configure terminal
ip tcp mss 2000
Example: Removing a Set IP TCP MSS
configure terminal
no ip tcp mss
Verifying IP TCP MSS
Command
Purpose
show ip tcp mss
Displays the set IP TCP MSS.
Additional References for IP TCP MSS
This section describes additional information related to configuring IP TCP MSS.