Re: [dnsop] Re: Root Anycast (fwd)

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On Thu, 30 Sep 2004, Iljitsch van Beijnum wrote:

> Note though that it's *very* hard to create a setup where packets are  
> delivered to different multicast instances, as it's hard to imagine how  
> any real-world anycast setup could match the criteria in

Its quite easy for anycast: (real names used, but not real relationships)

                Av8
              /   \
          sprint   att
              \   /
              F-root              


If Av8 turns on PPLB, traffic to F-root will go through both sprint and
att on a per-packet basis. However F-root is really anycasted, so it looks
really like this:

                              Av8

                          /           \
                  sprint                 att
                   |  |                  |  |
              ,----+--+--.            ,--+--+----.
              | router 1 |            | router 2 |  ...
              `--+-------'            `-------+--'
                 |                            |
              ,--+-------.            ,-------+--.
              | switch 1 +------------+ switch 2 |  ...
              `-+------+-'            `-+------+-'
                |      |                |      |
         ,------+-.  ,-+------.  ,------+-.  ,-+------.
         | f-root1|  | host 2 |  | f-root3|  | host 4 |  ...
         `--------'  `--------'  `--------'  `--------'
     
So, we see that some packets will go to f-root1 and some packets will go
to f-root3, on a per-packet basis. TCP will not work to an anycasted root
IF anyone on the internet uses PPLB and has the same peers/transit
providers as an anycasted root.

It might well be that packets from f-root1 and f-root3 both go through att
to Av8, assuming that f-root's operator doesn't use PPLB, but that doesn't
matter. The TCP connection can't be made or kept established.


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