RE: RFC3484 problem: scoping with site-locals/ULAs

["Durand, Alain" <Alain_Durand@cable.comcast.com>]

In my previous live, we were all using a large server for many things.
That server had 17 physical interfaces. Each interface had one IPv4
address
and 2 IPv6 addressses. Each client had also one IPv4 address and two
IPv6 addresses.

That makes the total combination: 17*2*2 for IPv6 plus 17*1*1 for IPv4,
that is 85.

Trying them all at the same time for potentially hundreds of clients,
many of them on different subnets than any of the 17 interfaces, is
overkill.

   - Alain.

  

> -----Original Message-----
> From: Fred Baker [mailto:fred@cisco.com] 
> Sent: Wednesday, May 10, 2006 11:31 AM
> To: Pekka Savola
> Cc: v6ops@ops.ietf.org; David Woodhouse; ipv6@ietf.org
> Subject: Re: RFC3484 problem: scoping with site-locals/ULAs
> 
> So I have a dumb question.
> 
> Why not:
> 	- use a DNS lookup that asks for all records (including 
> A, MX, and
> AAAA)
> 	- open both a v4 and a v6 connection simultaneously
> 	- accept the first to successfully open and shut down all others
> 
> Down sides: It gets all of the DNS data, which may be more 
> than it wanted to know, and it issues a second 
> SYN-or-whatever, and in the worst case one to each address. 
> But it deterministically finds a solution that works and 
> gives the system the service it is looking for.
> 
> I the big picture, the problem with that behavior is what?
> 
> On May 9, 2006, at 7:27 AM, Pekka Savola wrote:
> 
> > Hi,
> >
> > I was alerted to a practical deployment problem. As a result Linux 
> > glibc has started prefering IPv4 by default... so, I 
> believe we need 
> > to find a better solution.
> >
> > 1) v6 site-local address selection problems
> >
> > A site has deployed IPv6 site-local addresses (alongside with NATed 
> > v4).  They do not have global IPv6 reachability yet, but 
> want to test 
> > IPv6 alongside IPv4 internally.
> >
> > As a result, RFC 3484 address selection breaks: when trying 
> to connect 
> > to a hostname with a public IPv4 and IPv6 address, the host 
> will first 
> > try v6 fails (incurring about 3 min TCP timeout if ICMP 
> error is not 
> > sent), and after that connects to the v4 address.
> >
> > I.e., 'prefer matching scope' has v6 globals and site-locals, while
> > v4 has globals and private v4 addresses, and v6 wins, with bad 
> > results.
> >
> > An easy fix could be that v4 is preferable to v6 if both have 
> > mismatching scope as v4 is likely to be NATed while v6 isn't.
> >
> > Has anyone else run into this problem?  Is there something I'm 
> > missing?  What has been the implementation (or deployment) approach 
> > here?
> >
> > (I don't believe using RFC 4191 to advertise only the site-local 
> > prefix instead of a default route is a feasible solution here.
> > Likewise, requiring that routers will always send back an 
> ICMP error 
> > and the host gets it and honors it seems unfeasible in general.)
> >
> > 2) v6 ULA address selection problems
> >
> > Deploying ULAs doesn't help here, it just makes the problem 
> worse as 
> > you couldn't even use the 'matching scope' tweak.
> >
> > Do we need to specify that v6 ULAs should be treated as 
> "site scope" 
> > for the purposes of default address selection, or something else?
> >
> > Note that I do not believe it's sufficient to require that 
> each site 
> > (and each host within the site) deploys non-default RFC3484 
> policies.
> >
> > -- 
> > Pekka Savola                 "You each name yourselves king, yet the
> > Netcore Oy                    kingdom bleeds."
> > Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings
> 
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