Configuration Guide User guide

1056 FastIron Configuration Guide
53-1002494-02
IPv4 point-to-point GRE tunnels
Configuring GRE link keepalive
When GRE tunnels are used in combination with static routing or policy-based routing, and a
dynamic routing protocol such as RIP, BGP, or OSPF is not deployed over the GRE tunnel, a
configured tunnel does not have the ability to bring down the line protocol of either tunnel
endpoint, if the far end becomes unreachable. Traffic sent on the tunnel cannot follow alternate
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” on page 1059.
Configuring Path MTU Discovery (PMTUD)
Path MTU Discovery (PMTUD) support is described in the section “Path MTU Discovery (PMTUD)
support” on page 1045. 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:
Brocade(config-tnif-1)# tunnel path-mtu-discovery disable