Brocade BigIron RX Series Configuration Guide - Manual (Page 275)

BigIron RX Series Configuration Guide 197
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Configuring forwarding parameters
7
Changing the TTL threshold
The TTL threshold prevents routing loops by specifying the maximum number of router hops an IP
packet originated by the device can travel through. Each device capable of forwarding IP that
receives the packet decreases the packet’s TTL by one. If a device receives a packet with a TTL of 1
and reduces the TTL to zero, the device drops the packet.
The default TTL is 64. You can change the TTL to a value from 1– 255.
To modify the TTL threshold to 25, enter the following commands.
BigIron RX(config)# ip ttl 25
Syntax: ip ttl <1-255>
Enabling forwarding of directed broadcasts
A directed broadcast is an IP broadcast to all devices within a single directly-attached network or
subnet. A net-directed broadcast goes to all devices on a given network. A subnet-directed
broadcast goes to all devices within a given subnet.
NOTE
A less common type, the all-subnets broadcast, goes to all directly-attached subnets. Forwarding for
this broadcast type also is supported, but most networks use IP multicasting instead of all-subnet
broadcasting.
Forwarding for all types of IP directed broadcasts is disabled by default. You can enable forwarding
for all types if needed. You cannot enable forwarding for specific broadcast types.
To enable forwarding of IP directed broadcasts, enter the following command.
BigIron RX(config)# ip directed-broadcast
Syntax: [no] ip directed-broadcast
Brocade software makes the forwarding decision based on the router's knowledge of the
destination network prefix. Routers cannot determine that a message is unicast or directed
broadcast apart from the destination network prefix. The decision to forward or not forward the
message is by definition only possible in the last hop router.
To disable the directed broadcasts, enter the following command in the CONFIG mode.
BigIron RX(config)# no ip directed-broadcast
To enable directed broadcasts on an individual interface instead of globally for all interfaces, enter
commands such as the following.
BigIron RX(config)# interface ethernet 1/1
BigIron RX(config-if-e10000-1/1)# ip directed-broadcast
Syntax: [no] ip directed-broadcast
Disabling forwarding of IP source-routed packets
A source-routed packet specifies the exact router path for the packet. The packet specifies the path
by listing the IP addresses of the router interfaces through which the packet must pass on its way to
the destination. The device supports both types of IP source routing: