Configuring path mtu discovery – Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 User Manual
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Brocade ICX 6650 Layer 3 Routing Configuration Guide
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IPv4 point-to-point GRE tunnels
paths because the tunnel is always UP. To avoid this scenario, enable GRE link keepalive, which will
maintain or place the tunnel in an UP or DOWN state based upon the periodic sending of keepalive
packets and the monitoring of responses to the packets. If the packets fail to reach the tunnel far
end more frequently than the configured number of retries, the tunnel is placed in the DOWN state.
To enable GRE link keepalive, configure it on one end of the tunnel and ensure the other end of the
tunnel has GRE enabled.
To configure GRE link keepalive, enter commands such as the following.
Brocade(config)# interface tunnel 1
Brocade(config-tnif-1)# keepalive 12 4
These commands configure the device to wait for 4 consecutive lost keepalive packets before
bringing the tunnel down. There will be a 12 second interval between each packet. Note that when
the tunnel comes up, it would immediately (within one second) send the first keepalive packet.
Syntax: [no] keepalive seconds retries
Use the no form of the command to disable the keepalive option.
The seconds variable specifies the number of seconds between each initiation of a keepalive
message. The range for this interval is 2–32767 seconds. The default value is 10 seconds.
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,. For details, refer to
“Displaying GRE tunneling information”
Configuring Path MTU Discovery
Path MTU Discovery (PMTUD) support is described in the section
on page 96. 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.
Disabling and re-enabling PMTUD
PMTUD is enabled by default. To disable it, enter the following command:
Brocade(config-tnif-1)# tunnel path-mtu-discovery disable
To re-enable PMTUD after it has been disabled, enter the following command:
Brocade(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.
Brocade(config-tnif-1)# tunnel path-mtu-discovery age-timer 20