Re: IPv6 Formal Anycast Addresses and Functional Anycast Addresses (Fwd: New Version Notification for draft-smith-6man-form-func-anycast-addresses-01.txt)

Michael Richardson <mcr+ietf@sandelman.ca> Mon, 04 November 2019 00:26 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: 6MAN <6man@ietf.org>
Subject: Re: IPv6 Formal Anycast Addresses and Functional Anycast Addresses (Fwd: New Version Notification for draft-smith-6man-form-func-anycast-addresses-01.txt)
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Date: Sun, 03 Nov 2019 19:26:51 -0500
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Fred Baker <fredbaker.ietf@gmail.com>; wrote:
    > Funny. It doesn't work that way in DNS. Every root server simply thinks
    > that one of its addresses is the anycast address and so accepts the
    > packet as "directed to it". It also responds from that address, so that
    > the requester recognizes the response.

Yes, as long as it's UDP, or very short-lived TCP connections, it works.
If someone wants to use anycast for a longer-lived connection (in DNS, that
could include DoT...) then we run into problems.

{shim6 could have dealt with this, but we decided we couldn't do it. I'm
still sad}

    >> On Nov 3, 2019, at 4:27 PM, Toerless Eckert <tte@cs.fau.de>; wrote:
    >>
    >> It is somewhat architecturally dissatisfying that (AFAIK) we seem to need to
    >> resolve limitations of anycast addresses at the transport layer,
    >> e.g.: redirecting connection requests to an anycast address to a
    >> unicast address of the transport responder. If initiators would know an address is
    >> an anycast address, they could use some TBD network layer (ICMP) extension
    >> to do that resolution independent of individual transport protocols.
    >>
    >> And the network layer would only know it needed to do this if there was
    >> a way for the initiator to identify an address as an anycast address
    >> AFAIK (can't think of a simpler way).
    >>
    >> Cheers

--
Michael Richardson <mcr+IETF@sandelman.ca>;, Sandelman Software Works
 -= IPv6 IoT consulting =-