Re: Generic anycast addresses...

[Brian E Carpenter <[e-mail]>]

On 02-Jun-19 02:05, Michael Richardson wrote:
> 
> Mark Smith <[e-mail]> 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.

For example:

C:\WINDOWS\system32>tracert fd2e:82a1:f3c4::1

Tracing route to fd2e:82a1:f3c4::1 over a maximum of 30 hops

  1     2 ms     2 ms     2 ms  fritzy [fd63:45eb:dc14:0:be05:43ff:fe8e:ce39]
  2  General failure.

Trace complete.

fritzy is my CPE, of course.

> 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?

I think we need a better definition of scope boundaries, which clearly cannot be well defined just by bits in an address prefix. But I have a whole draft about that, and it's not particularly an IPv6 problem.

    Brian