Changing The Ttl Threshold; Configuring Dhcp Assist - Foundry Networks FESX Manual

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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 2 Switch can travel through. Each device capable of forwarding IP that receives the packet

decrements (decreases) the packet's TTL by one. If a router receives a packet with a TTL of 1 and reduces the

TTL to zero, the router 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:

FESX424 Switch(config)# ip ttl 25

FESX424 Switch(config)# exit

Syntax: ip ttl <1-255>

DHCP Assist allows a Foundry Layer 2 Switch to assist a router that is performing multi-netting on its interfaces as

part of its DHCP relay function.

DHCP Assist ensures that a DHCP server that manages multiple IP sub-nets can readily recognize the requester's

IP sub-net, even when that server is not on the client's local LAN segment. The Foundry Layer 2 Switch does so

by stamping each request with its IP gateway address in the DHCP discovery packet.

NOTE: Foundry Layer 3 Switches provide BootP/DHCP assistance by default on an individual port basis. See

"Changing the IP Address Used for Stamping BootP/DHCP Requests" on page 16-50.

By allowing multiple sub-net DHCP requests to be sent on the same wire, you can reduce the number of router

ports required to support secondary addressing as well as reduce the number of DHCP servers required, by

allowing a server to manage multiple sub-net address assignments.

December 2005

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