[quagga-dev 12909] Re: Question about Not allowing outside programs to remove Quagga routes

Greg Troxel gdt at ir.bbn.com
Thu Aug 6 19:15:32 BST 2015

Donald Sharp <sharpd at cumulusnetworks.com> writes:

> This patch changes the behavior of Quagga to reinstall routes, that were
> sourced from Quagga, back into the kernel if a route delete is received.
> David felt that this behavior was enough of a change that it should be
> brought to the list for discussion/decision.  The whole crux of the
> decision revolves around the question 'Who is the source of truth for
> routes?'.  We've written this patch because we believe that the answer to
> this question is that Quagga is the source of truth of routes if it is
> being run.

Definitely this needs discussion.  At first glance this seems like it
should be an option, not default behavior.

In a system with a kernel, quagga, and other things, there needs to be a
plan.  I see your point that if the plan is other than "quagga
controls", things are perhaps messy.  But quagga deals with static
routes that were already installed (leavint them, and redistributing
them) and I think would cope with newly-appearing static routes.

To make the plan work, the total system needs to be arranged so that
other things that modify routes don't fight quagga.  I can see why you'd
want quagga to put routes back, but if two programs play this game it's
just going to be a mess.

I think it would be helpful to hear about a situation where there is
some other program modifying the routing table while quagga is running
and where that isn't just a misconfiguration that should be corrected
(and then perhaps a reboot).   So far this seems like a workaround for
a wrong configuration and I don't see why it isn't better to expect
people to fix their misconfigurations.

An alternative approach could be to set some sort of ACLs and
permissions on routes so that non-quagga could not change quagga routes.

> Finally David also had some questions about how this could be done on BSD
> as well.

Looking at the patch, it seems to be at the zebra level and thus should
work the same way.  On BSD, the routing socket sends RTM_DELETE
messages, and this should get reflected into the zebra API.

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