Hi, JP
See in-line please.
> Hi Adrian,
>
> On Feb 5, 2007, at 7:11 PM, Adrian Farrel wrote:
>
>> Hi Greg,
>>
>>> - would you agree that usually ASBRs are eBGP speakers
>>> and are fully mesh connected. In that case eBGP can be
>>> viable solution for the inter-AS TE links computation by
>>> ASBR.
>>
>> So the question has to be:
>> Do other nodes apart from ASBRs need this information?
>>
>> What about an ingress LSR trying to compute a path out of the AS?
>>
>> If we require that the ingress LSR always consults an external PCE
>> that is a BGP speaker, then I guess this is fine, but most LSRs
>> today are capable of path computation and could handle this case
>> (for example, for the pd-path scenario) without needing to consult
>> an external PCE.
>>
>>> - I'm concerned with scaling aspect of flooding inter-AS TE
>>> information throughout both AS and an area
>>
>> I have this concern, too, but I wonder how many TE links we are
>> talking about, and how this compares with the number of TE links
>> within an area.
>>
>
> It is probably negligible ... Note that by contrast with the
approach
> proposing to flooding Inter-ASBR TE LSP, we're only looking at
> flooding the TE information of the inter-ASBR *links*.
>
>>> and I see that you're concerned as well (SHOULD for Type
>>> 10 and MAY for Type 11). I think that it would be
>>> helpful if use of both Type 10 and Type 11 for inter-AS
>>> TE Link advertisement be illustrated by scenarios. I think
>>> that use of area scope makes these OSPF extensions less
>>> applicable to inter-AS path computation by the head-end
>>> LSR/LER.
>>
>> Yes, that would be the case.
>
>> I agree that we need to look more closely at the scenarios. I
don't
>> think we have given enough thought to the nested domains case
(i.e.
>> areas in ASes) given that both pd-path and brpc (largely) treat
the
>> nested case as simply a flat sequence.
>
> Looking at the nested case, what would be the point of domain-scope
> since all TE-related info for the intra-area links have an area
scope ?
[ZRH]I try to give an answer.
With a new sub-tlv(remote AS number)and a new link type
(inter-AS link type) are specified, in a multi-areas AS, the entry
ASBR
when receving a path mesg can get the exit ASBR(in another area) with
this AS-scope advertisement and the path mesg(downstream AS number
is given in ERO). then, the inter-area computation can be performed.
Regards,
Zhang Renhai
>
>>
>>> - Could you please illustrate which links are excluded by the
>>> following:
>>> " Routers or PCEs that are capable of processing
advertisements of
>>> inter-AS TE links SHOULD NOT use such links to compute paths
that
>>> exit an AS to a remote ASBR and then immediately re-enter
the AS.
>>> Such paths would constitute extremely rare occurrences and MUST
>>> only
>>> be allowed as the result of specific policy configuration at
the
>>> router or PCE computing the path."
>>> Are there two links that interconnect a pair of ASBRs that belong
>>> to two
>>> different neighboring ASes?
>>
>> Renhai can comment, but I assumed that this meant that two ASes
are
>> linked by more than two TE links. The LSP should not under normal
>> circumstances leave AS1 to AS2 through TE link 1 and return to AS1
>> from AS2 through TE link 2.
>>
>> The example you give (ASBR1 in AS1 connects to ASBR2 in AS2 with
>> two links, the LSP goes out on one and back on the other) would be
>> detected as a loop in RSVP-TE, and would not offer any benefit
anyway.
>
> Thanks.
>
> JP.
>
>>
>> Regards,
>> Adrian
>
>