On 8/16/07, Stephen Hemminger [off-list ref] wrote:

The problem with socket options is how does the application know
the correct policy? Pushing configuration to application is just deferring
the problem, not solving it.  You want some policy to be done by the
infrastructure; that means kernel, libraries, daemons, etc. Doing it in
the application is often inflexible and unusable.

The policy will usually be done by the kernel. If the flag is not set,
which will happen most of the time, the driver will use a sensible
default ttl. The socket option would only be used by applications that
are specifically interested in a configurable ttl (like an application
to plot neighbors within an specific diameter). A per-interface
setting is not good enough, since we do not want the neighbor-plotting
tool to affect the ttl of other connections (e.g. a ssh session) that
might be going on at the same time.

-- 
Luis Carlos Cobo Rus       GnuPG ID: 44019B60
cozybit Inc.