Brocade Communications Systems ICX 7250 series, Configuration Manual

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NOTE
To prevent packet loss after the 24 byte GRE header is added, make sure that any physical interface that is carrying GRE tunnel
traffic has an IP MTU setting at least 24 bytes greater than the tunnel MTU setting. This configuration is only allowed on the
system if the tunnel mode is set to GRE.
Changing the maximum number of tunnels supported
Use the following table to determine how many GRE tunnels are supported. You can configure the device to support up to the maximum
number of GRE tunnels as displayed in the following table.
Device Max # of GRE tunnels Default # of GRE tunnels
ICX 7250 8 8
ICX 7420 64 16
ICX 7750 64 16
To change the maximum number of tunnels supported, enter commands such as the following.
device(config)# system-max gre-tunnels 16
Reload required. Please write memory and then reload or power cycle.
device(config)# write memory
device(config)# exit
device# reload
NOTE
You must save the configuration (write memory) and reload the software to place the change into
effect.
Syntax: system-max gre-tunnels number
The number variable specifies the number of GRE tunnels that can be supported on the device. The permissible range is 16 - 64. The
system-max gre-tunnels command determines the interface range that is supported for an interface tunnel. For example, if the system-
max value is reduced, it is possible that the configured interfaces may be rejected after a system reload.
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.
NOTE
Keepalives are not supported when a tunnel interface is not within the default-VRF.
To configure GRE link keepalive, enter commands such as the following.
device(config)# interface tunnel 1
device(config-tnif-1)# keepalive 12 4
IPv4 point-to-point GRE tunnels
Brocade FastIron Layer 3 Routing Configuration Guide
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