Hi Adrian!My comment is below.
Thank you.
SY,Boris
On Monday, June 1, 2020, 11:16:17 PM GMT+3, Adrian Farrel
<[email protected]> wrote:
Hello again,
[snip]
>>> 2) Fig 1, IMO, needs additional information about which AS/ ASes
>>> are used for Ingress and Egress SR Domains (Guess AS1 and AS2
>>> respectively, but it has to be shown). Current version looks a bit
>>> confusing, for example, why we need AS3 on Fig.1?
>>
>> I'm looking at the figure and I don't understand your confusion: sorry.
>> The ASes are not used for Ingress and Egress SR Domains. The two
>> domains are marked separately.
>> Packets are routed from the Ingress SR domain to the Egress SR
>> domain through the Gateways (also marked) and across the ASes
>> that provide connectivity.
>
> BKH> The text after Fig.1 says about limitations of BGP Add-Path
> especially in Inter-AS case with ASBRs in regards to GW identity,
> but Fig.1 also have AS3, it makes some dissonance with that
> message, IMO. That is why I was confused. May be I was just too
> focused on details :)
I’m not sure. Maybe if we had numbered the ASes differently so that the obvious
least AS-hops (“shortest”) path was through AS1, and AS2/AS3 was the path that
would lose the GW identities?
But I still don’t see the problem you are raising, and I really want to.
The figure shows that there are multiple possible routes from ingress domain to
egress domain:
- GW-AS3-GW2
- GW-AS1-[choice of ASBRs]-AS2-GW1
- GW-AS1-[choice of ASBRs]-AS2-GW2
The text notes that:
- Add-Paths enables the presentation of {AS3} and {AS1, AS2} as paths
- Add-Paths loses the identities and so choice of GW1 and GW2 in the {AS1,
AS2} case
BKH> I think, that t would be better to clarify the relationship between
Ingress and Egress SR domains with AS1,AS2,AS3 from BGP point of view on FIg 1.
Are they just part of AS3 (so IBGP between GW and PE of AS3) or separate ASes
(EBGP), it will be much easier to understand the further steps in regards to
why Add Path is not suitable there.
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