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Configuring IP
December 2000
15 - 35
Configuring Forwarding Parameters
The following configurable parameters control the forwarding behavior of Foundry 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’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, use either of the following methods.
USING THE CLI
To modify the TTL threshold to 25, enter the following commands:
BigIron(config)# ip ttl 25
Syntax:
ip ttl <1-255>
USING THE WEB MANAGEMENT INTERFACE
1.
Log on to the device using a valid user name and password for read-write access. The System configuration
panel is displayed.
2.
Click on the plus sign next to Configure in the tree view to display the list of configuration options.
3.
Click on the plus sign next to IP to display the list of IP configuration options.
4.
Select the General link to display the IP configuration panel.
5.
Enter a value from 1 – 255 into the TTL field.
6.
Click the Apply button to save the change to the device’s running-config file.
7.
Select the Save link at the bottom of the dialog. Select Yes when prompted to save the configuration change
to the startup-config file on the device’s flash memory.
Enabling Forwarding of Directed Broadcasts
A directed broadcast is an IP broadcast to all devices within a single directly-attached network or sub-net. A net-
directed broadcast goes to all devices on a given network. A sub-net-directed broadcast goes to all devices within
a given sub-net.
NOTE:
A less common type, the all-sub-nets broadcast, goes to all directly-attached sub-nets. Forwarding for
this broadcast type also is supported, but most networks use IP multicasting instead of all-sub-net 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, use either of the following methods.
USING THE CLI
BigIron(config)# ip directed-broadcast
Syntax:
[no] ip directed-broadcast
Summary of Contents for Switch and Router
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