On Nov 1, 2010, at 7:15 PM, Juliusz Chroboczek wrote: >>> Ah. You want the Babel network to be non-convex. Ouch. > >> I think a) giving each network disjoint sets of prefixes and b) making >> sure Babel never sees re-announcements from itself simplifies the >> problem to the point where it's workable. > > The attached *completely* *untested* patch implements the two new > features that you've asked for: > > - specifying "inherit" instead of a metric in a redistribute statement > causes the Babel metric to be 256 times the kernel priority; > - specifying "-k inherit" on the command line causes the kernel > priority of routes installed by Babel to be 1/256 of the Babel metric > (rounded up).
Great! One thing I don't understand: why is the priority multiplied/divided by 256 going into and out of the kernel? RTA_PRIORITY attributes appear to be a unsigned 32-bit int for both IPv4 and IPv6, which is more than enough to contain Babel metrics unmodified. > Once again -- it's completely untested. Even if it works, it will most > certainly cause transitory routing loops; and unless you're careful, it > will cause persistent routing loops. I think I see where you're coming from for both of these, but could you expound on the cases you had in mind? In particular, I don't think they affect my scenario -- I believe I can accomplish my goals by redistributing Babel into OSPF, not the other way around, and not Babel <-> OSPF <-> Babel. The only loops I can think of involve cases where a prefix falls off the network entirely, but that affects all Babel networks with overlapping announcements (e.g. default routes), whether redistributed across protocols or not. > This patch is not committed into the Babel tree. If you confirm that > your idea works (and manage to convince me), I'll consider making > a cleaner version for inclusion in Babel. I built a new image with the patched babeld and re-flashed my test Babel + OSPF device, and the babeld patch certainly appears to be working. I'm having an issue with getting Quagga 0.99.17 to read metrics from the kernel, and I haven't yet figured out exactly what's broken. (At the moment, I believe it picks up the RTA_PRIORITY from netlink routes on boot, but not on RTM_NEWROUTE events, so new/changed routes come up with metrics of 0.) My efforts so far have been hindered by a long compile/flash/test cycle and limited debugging tools, so I plan to re-work this section of my test network to include a normal Linux machine, and use it to get this resolved. Regardless, ospf6d announces external routes it learns from zebra as type 5 LSAs, and with a route map to set them to type 2 metrics, the Zebra route object's metric is copied into the announced cost. So, once I figure out where I'm losing metrics, we should be good. Thanks! --Will Glynn _______________________________________________ Babel-users mailing list [email protected] http://lists.alioth.debian.org/mailman/listinfo/babel-users
