A router sends an ICMP Redirect frame to a host to tell the host that the
host has a more direct route to a destination.
In the Redirect frame, the router says which device the host should send
the frame to. In some cases, the host can reach the destination directly.
This can happen when you have two IP subnets on the same interface (because
of a VLAN design perhaps). The hosts think they have to use the router, but
the router knows that the hosts can reach other directly.
In some cases, the router tells the host to use a different router. You
might have two routers on an Ethernet segment. Which do you use for the
default gateway for the hosts? Well, it often doesn't matter, especially
since, if a host uses the less optimal router, that router sends an ICMP
Redirect specifying the more optimum router to use. (The scenarios are
difficult to explain without a whiteboard! &;-)
The reasons for turning ICMP Redirect off usually have to do with control,
security, and performance. When a host receives the ICMP Redirect, it is
supposed to thereafter use the new route for this destination. Perhaps
that's not what you want. Perhaps you want to make sure all traffic goes
through the default router where you have security or performance features
configured.
Another reason to turn it off is that it doesn't really do much good. Since
hosts generally revert to using their default gateway for every new session
anyway, it's a waste of bandwidth for the router to send Redirects.
Priscilla
At 07:17 AM 12/5/00, FREDL L AZARES wrote:
>What's the purpose of no ip redirects in VLAN ehternet subinterface
>configuration? Thanks in advance.
>
>Fredl Azares
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