Quick Reference Guide

592 PowerConnect B-Series TI24X Configuration Guide
53-1002269-02
Configuring IP parameters – Layer 3 Switches
21
Configuring forwarding parameters
The following configurable parameters control the forwarding behavior of Layer 3 Switches:
• Time-To-Live (TTL) threshold
• Forwarding of directed broadcasts
• Forwarding of source-routed packets
• Ones-based and zero-based broadcasts
All these parameters are global and thus affect all IP interfaces configured on the Layer 3 Switch.
To configure these parameters, use the procedures in the following sections.
Changing the TTL threshold
The 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 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.
PowerConnect(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.
PowerConnect(config)#ip directed-broadcast
Syntax: [no] ip directed-broadcast
NOTE
This command is not supported on the PowerConnect B-Series TI24X devices.
Device 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.