On 13-11-03 02:27 PM, Loïc BLOT wrote:
then to explain my draft here is my own configuration, and why it could be useful to set custom priorities: [...] Without the possibility to change the priorities (and dynamically is better than recompile the kernel and change constant values, it would be a great function to everybody want), it's impossible to solve this routing loop (i have patched ospfd to refuse adding some specific routes from specific hosts but it's not a proper solution, whereas it worked...).
FWIW, I agree with Loïc on this; a router administrator should be able to have fine-grained control over route preference.
I've run into this in the past, where in a strange topology I wound up with a router (not OpenBSD) learning the same route via EIGRP, OSPF and BGP - each with a different next-hop. Only one of those used the preferred (low-latency, high-bandwidth) path, I don't recall which, but we did have to manually adjust the local preference of one of the protocols in order to make it "win".
Policy routing would not (could not) have solved the problem, since it was all dynamic routes.
I'm about to re-build something similar, actually, using BGP and OSPF (or possibly BGP and static routes), where I will need the ability to control which routing protocol takes precedence. I'll have a route learned via BGP that I want used first, and a route learned by OSPF that I want used only if the BGP route vanishes. (It's a partial overlay network, with backup link over VPN to maintain control functions in the case of an outage on the main link which talks BGP to its peer.)
However... in reading route(8), I see the "-priority" flag exists. Delving a bit deeper into .../net/route.h, I see that the routing table *already has* exactly the support I need (and that I think Loïc needs) in "rt_priority" and the associated macros.
The change I think we're both asking for is that in .../usr/sbin/bgpd/kroute.c, on line 505 (5.4-RELEASE), where we see "kr->r.priority = RTP_BGP;", we need a way to override that value in (presumably) bgpd.conf. (Ditto for the IPv6 function.)
Similarly, in .../usr/sbin/ospfd/kroute.c:257, where we have "kn->r.priority = RTP_OSPF;", and presumably the same sort of thing in routed(8), ripd(8), ospf6d(8), possibly even ldpd(8)...
I believe all the support we need is already in the kernel, what we lack is a user-exposed knob to fiddle with those (for now) constant values. I believe they should be default values, not constant values.
I believe it is possible to work around this problem currently with "route change", but doing so is a very, very ugly idea (worse in Loïc's case than mine, I think). You'd have to have a script/daemon of your own watching the output from "route monitor" and executing "route change" every time a route gets inserted with the wrong priority. This leads to much duplication of routing logic, since the correct route is not always known a priori.
-- -Adam Thompson athom...@athompso.net
