re: [RRG] ALT's strong aggregation often leads to *very* long paths

[Xu Xiaohu <xuxh@huawei.com>]

>    LISP-ALT routers are deployed in a hierarchy which matches the
>    EID prefix allocation hierarchy.  LISP-ALT routers at each level
>    in the this hierarchy are responsible for aggregating all EID
>    prefixes learned from LISP-ALT routers logically "below" them and
>    advertising summary prefixes to the LISP-ALT routers logically
>    "above" them.
Does LISP-ALT seem like a variation or a simplified instance of LISP-CONS? 
Both of them introduce a hierarchical overlay network which is
topology-independent. The difference is: in LISP-CONS, the overlay network
is just used for mapping query and reply. While in LISP-ALT, the overlay can
also be used for forwarding the initial traffic in order to solve the
initial packets loss in ITR when cache missed. Is that correct?

> This is presumably impossible at the edge of the network, since the
> location of ETRs for a given EIDs are scattered around the place
> with little or no correlation with geography. 
...
> By mandating the structure of the ALT network be strongly driven by
> address aggregation, this means the connections between one router
> and the next in the hierarchy will have little or no relation to
> geography.  Therefore, the average length of inter-router distance
> will be far longer than for ordinary BGP routers, where the network
> structure is based primarily on linking to geographic neighbours,
> and not at all on address aggregation.
If the overlay network is used for traffic forwarding, what you mentioned is
inevitable. And if the usage of PI address is desired and encouraged, the
major assumption of ALT will have not a leg to stand on and the things will
become worse.

Xiaohu XU


--
to unsubscribe send a message to rrg-request@psg.com with the
word 'unsubscribe' in a single line as the message text body.
archive: <http://psg.com/lists/rrg/> & ftp://psg.com/pub/lists/rrg