Tony –

Not sure why this needs to be explained.
Whether you are doing label forwarding or IP forwarding, the path of the packet 
still depends upon reaching the destination.
If I have a unicast destination then the packet needs to reach the unique 
advertiser of that destination.
If I have an anycast destination then the packet needs to reach only one of the 
possibly many advertisers of that destination.

Are you proposing for “Area SID” that we tie the SID to a prefix but alter the 
logic such that nodes which do not advertise the prefix can be considered as 
the final destination?
I would not like to go down that path…


From: Tony Li <>
Sent: Thursday, August 06, 2020 9:32 AM
To: Les Ginsberg (ginsberg) <>
Cc: Acee Lindem (acee) <>; Bruno Decraene 
Subject: Re: [Lsr] draft-ietf-lsr-isis-area-proxy-02


 There then remains the question as to whether the “Area Prefix” is anycast or 
unicast i.e., is it common to all IERs or is it unique to whomever gets elected 
Area Leader?

Does it matter? We have no clear semantics for this prefix. A difference that 
makes no difference is no difference.

[Les:] This question needs to be directed at those who prefer the Area Prefix 
approach. It matters as it impacts configuration and advertisement semantics. 
An anycast prefix is NOT a Node Prefix.
And it impacts how traffic is forwarded into the area.

How so?  Traffic will be directed to the SID value (modulo PHP).
[Les3:] If the prefix is private to a single router then traffic has to pass 
through that router. If it is anycast the traffic could arrive at any one of 
the routers supporting the anycast address.

I must be missing something. My understanding of SR is that you forward based 
on the label.  Please educate me.


Lsr mailing list

Reply via email to