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Re: Generic anycast addresses...

Michael Richardson <mcr+ietf@sandelman.ca> Sat, 01 June 2019 14:05 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Mark Smith <markzzzsmith@gmail.com>
cc: Ted Lemon <mellon@fugue.com>, 6MAN <6man@ietf.org>
Subject: Re: Generic anycast addresses...
In-Reply-To: <CAO42Z2x9iTrbvZuCxqSpDX-CQ9MtY8V1yyb-hg+XYtXXYn7LKg@mail.gmail.com>
References: <D22E680C-3EE3-4AD7-90C0-9339DA2E5A29@fugue.com> <BN6PR21MB04978DB375C05CB3CE4C914EA31F0@BN6PR21MB0497.namprd21.prod.outlook.com> <4EF97F31-1F39-4150-B044-955C46E96FB4@fugue.com> <20190530002833.wfvjfbj2lv2ig664@faui48f.informatik.uni-erlangen.de> <7A9560FC-0393-45DF-8389-B868455AC6DD@fugue.com> <20190530005734.7d2alod2zoaemmhc@faui48f.informatik.uni-erlangen.de> <D6E27B45-437F-45BE-A305-47DD460BCE02@fugue.com> <26144.1559226966@localhost> <1DD451A7-D898-4105-974C-53776A3DA9F2@fugue.com> <20190530152902.l2nmyhadr4e4kt7x@faui48f.informatik.uni-erlangen.de> <0FF19D6D-1A45-41EF-BE34-CC35B5E51E1E@steffann.nl> <D91629F6-73AC-4A80-80EF-16644F73DA36@fugue.com> <701687d4-842c-6a16-3c97-349125324e3f@gmail.com> <D648647D-60E1-4DCE-B0BE-11002E0AE5A4@fugue.com> <25631.1559317738@localhost> <CAO42Z2x9iTrbvZuCxqSpDX-CQ9MtY8V1yyb-hg+XYtXXYn7LKg@mail.gmail.com>
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Date: Sat, 01 Jun 2019 10:05:08 -0400
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Mark Smith <markzzzsmith@gmail.com> wrote:
    >> hop 1 is the router at home, and hope 2 is the access router at my ISP, and
    >> hop 3 is my ISP's core router connect to upstream peers.
    >>
    >> Should hop 1 (home router) or hop 2 (access node) were to blackhole route
    >> fc00::/6 (ULA-R and ULA-C), would that affect your use case?  Or could the
    >> anycast service possibly be at the ISP?

    > I'm guessing you don't have internal ULA address space, which is why you're
    > more successful than if you did.

I do have a lot of ULA, but I didn't try from within those segments, because I
was not at my office and I couldn't get there from the conference I was at.

    >> Should home routers install routes to 2000::/3 when they see "default"
    >> rather
    >> than "::/0"?  I have made that argument, but I see the other point about
    >> how limiting it could be in the future.

    > A ULA address at an ISP would only be reachable to customers who only have
    > GUA addresses.

    > If a customer has ULA internally, a ULA source address would be preferred
    > over a GUA source to reach an ISP ULA (anycast) destination. That ULA
    > source address would cause the packet to be dropped by a BCP38 filter at
    > the ISP access router, assuming they have them, as they should.

    > Even if the ISP doesn't have BCP 38 filters, the ISP's routing is very
    > unlikely to have routes back to all customers' ULA address spaces.

This is a good point you make.
So should home routers do BCP38 filtering on their external interface?
(Better to drop it early)

    > So you need global scope anycast addresses for working source address
    > selection. Except that defeats the goal of having anycast destined packets'
    > travel being restricted to a domain smaller than global when that is
    > required or desirable.

Do you think we need another scope of address?

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

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