Hi Peter.
On 26 Aug 2014, at 16:43, Peter Psenak <[email protected]> wrote:
>
> On 8/26/14 17:32 , Hannes Gredler wrote:
>>
>> operators want to assign node-tags as per router function (ABR, PE, core)
>> and then
>> the LFA-selection becomes much easier to specify. - e.g.
>> - only pick a LFA that does not cross another PE router.
>>
>> similarily it is desirable for "LFA tunnel termination"
>> to put out a constraint which says
>> - only pick a PQ neighbor which has node tag 'X'
>
> my point is that with the above approach you have to:
> 1. On candidate PQ nodes configure the tag X
> 2. on all other nodes configure "only pick a PQ neighbor which has node tag
> 'X'"
>
> It's (2) which makes me feel uncomfortable, as it's a config to be applied to
> many nodes.
I’m unclear on how one would solve this — the key thing is that there are
number of scenarios where it is *operator* preference rather than node
capabilities that mean that we want to select a particular node for some
certain application. This preference may be on a per-calculating node basis. If
this is the case, then a single capability that says that a particular target
node is capable of acting in a particular role is not sufficient.
(Consider this scenario:
- rtr-A is in country 1.
- rtr-B is in country 2.
- Both rtr-A and rtf-B are capable of acting as PQ nodes,and need to
act as such for ‘local’ nodes (i.e., those in the same country as them).
- rtr-A should never select rtr-B as a PQ.
In this case, we need some tag that specifies country, as well as some tag that
specifies that it is a valid PQ node. We then need specific policy on rtr-A and
rtr-B to implement this policy.)
It is very typical that where we have such policy implementations, then we need
to configure the behaviour on a per-node basis. This is especially true where
policies must consider characteristics of the topology.
>>
>> i found it always strange that we for TE (as an example for
>> constraining paths) we have got ways to tag links, but
>> not way to tag nodes - that draft aims to fix that.
>
> I'm not against tagging nodes as such. What worries me if we end up using
> node tags for signalling capabilities of node.
As per the above, I do not think that this mechanism replaces any capability,
it just gives an operator a means to be more granular than the binary
“supported”/“not supported” view that a flag indicating capabilities does.
I, of course, support the adoption of this draft as a co-author.
Cheers,
r.
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