Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 - Manual (Page 122)

104 Brocade ICX 6650 Layer 3 Routing Configuration Guide
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IPv4 point-to-point GRE tunnels
Changing the MTU value for a tunnel interface
For important configuration considerations regarding this feature, refer to “GRE MTU configuration
considerations” on page 99.
You can set an MTU value for packets entering the tunnel. Packets that exceed either the default
MTU value of 1476/10194 bytes (for jumbo case) or the value that you set using this command, are
fragmented and encapsulated with IP/GRE headers for transit through the tunnel (if they do not
have the DF bit set in the IP header). All fragments will carry the same DF bit as the incoming
packet. Jumbo packets are supported, although they may be fragmented based on the configured
MTU value.
The following command allows you to change the MTU value for packets transiting “tunnel 1”:
Brocade(config)# interface tunnel 1
Brocade(config-tnif-1)# ip mtu 1200
Syntax: ip mtu packet-size
The packet-size variable specifies the maximum size in bytes for the packets transiting the tunnel.
Enter a value from 576 through 1476. The default value is 1476.
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
By default, Brocade ICX 6650 IPv6 devices support up to 32 GRE tunnels. You can configure the
device to support 16–64 GRE tunnels. To change the maximum number of tunnels supported,
enter commands such as the following.
Brocade(config)# system-max gre-tunnels 16
Reload required. Please write memory and then reload or power cycle.
Brocade(config)# write memory
Brocade(config)# exit
Brocade# 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