tcp-mss (Protocols BGP)
Syntax
tcp-mss segment-size;
Hierarchy Level
[edit logical-systems logical-system-name protocols bgp], [edit logical-systems logical-system-name protocols bgp group group-name], [edit logical-systems logical-system-name protocols bgp group group-name neighbor neighbor-name], [edit logical-systems logical-system-name routing-instances routing-instance-name protocols bgp], [edit logical-systems logical-system-name routing-instances routing-instance-name protocols bgp group group-name], [edit logical-systems logical-system-name routing-instances routing-instance-name protocols bgp group group-name neighbor neighbor-name], [edit protocols bgp], [edit protocols bgp group group-name], [edit protocols bgp group group-name neighbor neighbor-name], [edit routing-instances routing-instance-name protocols bgp], [edit routing-instances routing-instance-name protocols bgp group group-name], [edit routing-instances routing-instance-name protocols bgp group group-name neighbor neighbor-name]
Description
Configure the maximum segment size (MSS) for the TCP connection for BGP neighbors.
You can set the MSS globally or for a particular neighbor. If the router receives a
TCP packet with the SYN bit and the MSS option set, and the MSS option specified in
the packet is larger than the MSS value specified by the tcp-mss
statement, the router replaces the MSS value in the packet with the lower value
specified by the tcp-mss statement.
The MSS is only valid in increments of 2 KB. The value used is based on the value set, but is rounded down to the nearest multiple of 2048.
This configuration statement is for host-originated packets. To configure the TCP MSS value for transit traffic on a particular interface, see tcp-mss (Interfaces) .
There
are multiple factors that define the MSS value for TCP packets, which are reflected
in the MSS value displayed in the output of the show system connections command:
-
The MSS value offered by the peer in the SYN packet.
-
Rounding the MSS off to the nearest multiple of 2048.
-
The MTU value of the interface.
-
The configured path MTU value.
-
Whether TCP sessions are not directly connected and path MTU discovery is disabled.
-
Whether the TCP sessions are on a directly-connected network.
Limitations
-
The
tcp-mssconfiguration is not supported for dynamic (allow) or auto-discovered BGP peers. This limitation exists due to the current BGP session establishment design in the operating system, which does not apply the TCP MSS setting to sessions formed with dynamically discovered peers. -
This setting is effective only for statically configured BGP neighbors.
Options
| segment-size | MSS for the TCP connection.
|
Required Privilege Level
routing—To view this statement in the configuration.
routing-control—To add this statement to the configuration.
Release Information
Statement introduced in Junos OS Release 8.1.