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… Les From: Tony Li <tony1ath...@gmail.com> Sent: Thursday, August 06, 2020 9:32 AM To: Les Ginsberg (ginsberg) <ginsb...@cisco.com> Cc: Acee Lindem (acee) <a...@cisco.com>; Bruno Decraene <bruno.decra...@orange.com>; email@example.com Subject: Re: [Lsr] draft-ietf-lsr-isis-area-proxy-02 Les, 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. Tony
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