[quagga-dev 10872] Re: [PATCH 2/4] zebra: quagga-re-onlink-support.patch

James Li jli at cumulusnetworks.com
Tue Oct 29 16:37:35 GMT 2013


On 10/29/13 6:44 AM, Christian Franke wrote:
> On 10/29/2013 01:40 PM, Joakim Tjernlund wrote:
>> Christian Franke <chris at opensourcerouting.org> wrote on 2013/10/29 12:39:40:
>> We could limit this to /32 masks(aka unnumbered) to begin with if that
>> is the only need today.
> I would be interested whether this is considered sufficient, especially
> by the babel folks, but of course by any other potential users as well.
>
>>> One question that comes to my mind, though: Wouldn't it then be easier
>>> to just always set onlink when we encounter ZEBRA_NEXTHOP_IPV4_IFINDEX?
>>> The only difference that I see is that a route installed without onlink
>>> will be removed from the FIB when the matching IP-Network is
>>> deconfigured from the outgoing interface.
>>> In that case, Zebra would notice that the route is gone and readd it
>>> with onlink set if your suggested change was implemented, wouldn't it?
>> hmm, will Q mess with routes that wasn't added by Q in the first place?
>> Or am I misreading this?
> I made a wrong assumption there, the kernel won't even remove a route of
> which the nexthop becomes unreachable.
>
> What I meant, and what is still (more) valid: It seems that the only
> thing onlink is doing, is overwriting the reachability check for the
> gateway when installing the route into the kernel.
>
> So why should we set onlink only when the nexthop is not reachable? If
> the nexthop is reachable, setting onlink wouldn't change the semantics
> anyway, would it?

The question is: do we still want the check to be there for certain 
cases, say numbered interface. I would think yes, the gateway address 
needs to be in the same subnet for numbered interface. For unnumbered, 
we set the onlink flag; for numbered, we don't. Unless for numbered we 
are not using ZEBRA_NEXTHOP_IPV4_IFINDEX?
James

> (That general point is only valid if we set onlink for any configured
> netmask. It doesn't apply if we only do that for /32)
>
> -Christian
>
>
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