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Hierarchy Level


Enable and specify the TCP maximum segment size (TCP MSS) for Generic Routing Encapsulation (GRE) packets that are coming out from an IPsec VPN tunnel. If the device receives a GRE-encapsulated TCP packet with the SYN bit and TCP MSS option set and the TCP MSS option specified in the packet exceeds the TCP MSS specified by the device, the device modifies the TCP MSS value accordingly. By default, a TCP MSS for GRE packets is not set.


mss value —TCP MSS for GRE packets. Value is optional.

  • Range: 64 through 63535 bytes

  • Default: 1320 bytes, if no value is specified

Required Privilege Level

security—To view this in the configuration.

security-control—To add this to the configuration.

Release Information

Statement introduced in Junos OS Release 8.5.