dhclient dry-run - need to know the def gateway without installing the def route
alessandro.macuz at gmail.com
Mon Apr 7 20:23:32 UTC 2014
2014-04-07 21:15 GMT+02:00 Simon Hobson <dhcp1 at thehobsons.co.uk>:
> alessandro macuz <alessandro.macuz at gmail.com> wrote:
> > I could deduce the gateway from the DHCP server IP address because
> normally they coincide but that would be my assumption.
> You've heard the expression that "assume" makes an "ass" out of "u" and
> "me", well your assumption is badly wrong. In home and small networks it is
> likely to be true (not mine though). But once you get to business networks
> then its more likely that the DHCP server is not at the same IP address as
> the router.
However, I'm still not quite sure why you are doing things the long way
> round. What's specifically wrong with using the route that comes with the
> lease ? Or more to the point, what's wrong with dealing with it when you
> get it ? And BTW - have you considered the possibility of getting different
> answers to your two queries ?
Sorry maybe I should have added more details but there is only one defaut
gateway on the network of that interface and hence the dry-run returns
always the same IP address. As to the second reply it will configure the
Why I want to run a dry-run? Because eventually I need to install some
routes pointing to the only gateway on the network. On the system there is
another interface that gets the IP dinamically and two default routes are
> For many clients (certainly the ISC one on Linux) you can supply your own
> script/modify the stock one. That means you can go and accept a lease, then
> use your own script to fiddle with the system. Or at least I thin that's
> the case.
I thought of this and delete the 2nd def route but even if for less than a
second packets would load-balanced between the two default routes. Now that
I'm writing I realize that the loadbalancing mechanism is in place only
when the adm distance is the same, so maybe I can play with that value if
the DHCP protocol allows that.
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