topic Re: default route precedence in Operating System - HP-UX

default route precedence

Jay Cantwell — Fri, 24 Jun 2005 08:01:30 GMT

I tried looking through some threads and could not find a cut and dry answer to my question:

How does routing precedence take place, is the default route used first, and then statics?

Or are the static routes looked at first, and if they are not found then the default is used?

thanks...Jay

Re: default route precedence

Jeff Schussele — Fri, 24 Jun 2005 08:20:36 GMT

Hi Jay,

As I understand it, it all depends on how you construct the routes.
IF you set up the static routes as 0 hop & indicate the local I/F as the gateway then any traffic destined to that route will go out the specified I/F. All other traffic will go out to the default gateway.

HTH,
Jeff

Re: default route precedence

Jay Cantwell — Fri, 24 Jun 2005 08:26:07 GMT

Hi Jeff....

Okay with the 0 hops, unfortunately I have to set up my routes with a hop count of 1. How does this change the use of the route table ?

Jay

Re: default route precedence

C. Beerse_1 — Mon, 27 Jun 2005 04:00:55 GMT

afaik, the default route is only used where the other (static) routes do not match for the target.

Only where there are more routes to the target (like multiple default routes) then all routes will be used in some order. Some routers count hops, some use metrics, check the manual for your route software for details. As far as I read `man route` on hpux, there is not much to define.

Re: default route precedence

rick jones — Mon, 27 Jun 2005 12:12:21 GMT

Closer matches to the destiation IP addresses are used first, so that would be:

1) matching host routes
2) matching (sub)network routes
3) default route

IE the default route is used last. As someone else pointed-out, when there are two otherwise identical routes, the metric will be used to pick. If the metric is the same, then it should assumed to be chance as to which is used first. Never assume that first or last set will be the order when the routes are otherwise identical.

If ip_strong_es_model is set, then source IP address as well as destination IP address is included in the route lookup, and routes with matching source IP's are used first. I do not know however, if a networking route with a matching source IP would "trump" a specific host route without matching source IP. That much has not come-up before :)