if-up is creating route entry for

All,

The following section of /etc/.../if-up in both RH9 and FC1
appears to be creating extranous route table entries.
Sometime they show up with eth0 and sometimes with usb0.

What is causing this??

# Add Zeroconf route.
if [ -z "${NOZEROCONF}" -a "${ISALIAS}" = "no" ]; then
ip route replace 169.254.0.0/16 dev ${REALDEVICE}
fi

Thanks,
Dan



dan

dan wrote:
> All,
>
> The following section of /etc/.../if-up in both RH9 and FC1 appears to
> be creating extranous route table entries. Sometime they show up with
> eth0 and sometimes with usb0.
>
> What is causing this??
>
> # Add Zeroconf route.
> if [ -z "${NOZEROCONF}" -a "${ISALIAS}" = "no" ]; then
> ip route replace 169.254.0.0/16 dev ${REALDEVICE}
> fi
>

IP addresses in the 169.254/16 range are reserved for use on the local
data link. These "link local" IP addresses are not routable, and they
are used with autoconfiguration schemes (see also "ZEROCONF").

Link local IP addresses serve a number of purposes. For example: If a
DHCP client tries to lease an IP address from a DHCP server and the
lease attempt fails, the DHCP client can, as a "plan B", try to allocate
itself a link local IP address instead. Granted, a link local IP address
is not routable, and therefore can only be used to communicate with
hosts on the local data link. However, system designers often feel that
having a link local IP address is better than having no IP address at all.

Another common use for link local IP addresses is roaming. For example,
a laptop with a wireless card can try to autoconfigure itself with a
link local IP address when it enters the service area of a wireless base
station. The laptop can then communicate with the other hosts on the
local data link (i.e., in the base station's service area) using its
link local IP address.

Most OS environments these days (Win32, MacOS, Linux, etc.) support link
local IP addresses - e.g., they implicitly add an entry for the
169.254/16 address range in a host's routing table.

Here's some additional info on link local IP addresses and their uses,
if you're interested:

http://files.zeroconf.org/draft-ietf...-linklocal.txt
http://www.ittc.ku.edu/~amitk/801/801-doc.html
http://www.faqs.org/rfcs/rfc3330.html

--
Jim

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