Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 60)

Changing the TTL threshold
The time to live (TTL) threshold prevents routing loops by specifying the maximum number of router
hops an IP packet originated by the Layer 3 switch can travel through. Each device capable of
forwarding IP that receives the packet decrements (decreases) the packet 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 value for the TTL threshold is 64. You can change the TTL threshold to a value from 1
through 255.
To modify the TTL threshold to 25, enter the ip ttl command.
device(config)# ip ttl 25
Syntax: ip ttl ttl-threshold
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 ip directed-broadcast command.
device(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 no ip directed-broadcast command in the CONFIG
mode.
device(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.
device(config)# interface ethernet 1/1
device(config-if-1/1)# ip directed-broadcast
Syntax: [no] ip directed-broadcast
Changing the TTL threshold
60 FastIron Ethernet Switch Layer 3 Routing Configuration Guide
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