Brocade Communications Systems FastIron SX 800 Configuration Manual page 114

IPv4 point-to-point GRE tunnels
The retries variable specifies the number of times that a packet is sent before the system places the tunnel in the DOWN state. Possible
values are from 1 through 255. The default number of retries is 3.
Use the show interface tunnel and show ip tunnel traffic commands to view the GRE link keepalive configuration.
Configuring Path MTU Discovery (PMTUD)
PMTUD is enabled by default on tunnel interfaces. This section describes how to disable and re-enable PMTUD on a tunnel interface,
change the PMTUD age timer, manually clear the tunnel PMTUD, and view the PMTUD configuration.
NOTE
For the SX-FI8GMR6, SX-FI2XGMR6, SX-FI624HF, SX-FI624C, SX-FI624P, and the SX-FI62XG modules, all fragments will
carry the same DF bit as the incoming packet. For the SX-FI-24GPP, SX-FI48GPP, SX-FI-24HF, SX-FI-2XG, and SX-FI-8XG
modules and the FCX modules, the DF bit on the outer IP header after encapsulation will be set if the PMTU is enabled. If
PMTU is disabled, the DF bit will be unset irrespective of the DF bit of the incoming packet.
Disabling and re-enabling PMTUD
PMTUD is enabled by default. To disable it, enter the following command:
device(config-tnif-1)# tunnel path-mtu-discovery disable
To re-enable PMTUD after it has been disabled, enter the following command:
device(config-tnif-1)# no tunnel path-mtu-discovery disable
Syntax: [no] tunnel path-mtu-discovery disable
Changing the age timer for PMTUD
By default, when PMTUD is enabled on a tunnel interface, the path MTU is reset to its original value every 10 minutes. If desired, you
can change the reset time (default age timer) to a value of up to 30 minutes. To do so, enter a command such as the following on the
GRE tunnel interface.
device(config-tnif-1)# tunnel path-mtu-discovery age-timer 20
This command configures the device to wait for 20 minutes before resetting the path MTU to its original value.
Syntax:[no] tunnel path-mtu-discovery { age-timer minutes | infinite }
For minutes , enter a value from 10 to 30.
Enter infinite to disable the timer.
Clearing the PMTUD dynamic value
To reset a dynamically-configured MTU on a tunnel Interface back to the configured value, enter the following command.
device(config)# clear ip tunnel pmtud 1
Syntax: clear ip tunnel pmtud tunnel-ID
The tunnel-ID variable is a valid tunnel number or name.
114
FastIron Ethernet Switch Layer 3 Routing
53-1003627-04