SUMMARY change default route

From: Ellen Davis <daviser_at_email.uc.edu>
Date: Wed, 10 Feb 1999 10:15:22 -0500

Thanks to all for the quick responses.

"Michael Matthews" <mike_at_matthews.net>
Ralf Lehmann <rl1_at_irz301.inf.tu-dresden.de>
Matt Harrington <matth_at_itsa.ucsf.edu>
"Leonard, Roger" <rleonard_at_cvty.com>
Robert Otterson <Robert.Otterson_at_digital.com>
wmills_at_WellsFargo.COM
Phil Thomas <Phil.Thomas_at_digital.com>
Girish Phadke <pgirish_at_maxisnet.com.my>
Arnaud valeix <arnaud.valeix_at_sncf.fr>
Pascal Van Bever <Pascal.VanBever_at_digital.com>
Jim Bostwick <Jim_Bostwick_at_cargill.com>

My original question:
>Can I change the default route without having to reboot the machine and
>knock off all my users?
>
>I am having a networking problem and the network guys here want me to use a
>different default route. My route is currently defined in /etc/route and I
>am running gated (if it matters). Oh, the machine is running DU4.0D.

Phil Thomas summed it up the best. One caution, make sure the new route is
a correct route. I ended up needing to reboot the system for another
purpose, so I simply changed /etc/routes and rebooted.

---Phil Thomas <Phil.Thomas_at_digital.com>

gated will generally prevent you from removing routes on-the-fly with the
route(8) command, however you can follow this procedure...

1. update /etc/routes with the new default route
2. kill gated with "gdc KILL", which prevents gated from cleaning up
(note: "gdc stop" will also stop the gated, however it allows the daemon to
remove from the kernel all the routes it entered -- i.e. the system will
lose connectivity to remote subnets until gated comes back and repopulates
the kernel routing table.)
3. remove the current default route with "route delete default <whatever>"
4. add the new default route with "route add default <whatever-new>"
5. restart gated with "gdc start"

WARNING: if you're dealing with a production system that has users on remote
subnets there is the potential for a service outage if anything goes wrong
during this process. If there's anything significant riding on the
availability of the system (like your job...) you should take steps to avoid
or limit possible impact! (test on another system, apply the change out of
hours, ...)

Complications aside, however, this process will switch the default route
without affecting connectivity. All you may lose is a minute of route
updates, and the whole process should take less than a minute.

(And having said all this, you may want to try just steps 1, 3, 4 on their
own first to see if gated will let you adjust the default route without
restarting gated. I expect that you may already have tried this.)

Also note that it is possible to import the default route through a routing
protocol, however a locally defined static route will normally take
preference over an imported one.

man gdc(8), gated(8), gated.conf(8) for more info about gated routing.
-----

 Ellen Davis
 Ellen.Davis_at_uc.edu
Received on Wed Feb 10 1999 - 15:15:30 NZDT

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