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Re: Deploying IPv6 in a datacenter (Was: Awful quiet?)

  • From: James
  • Date: Wed Dec 21 09:22:18 2005

On Wed, Dec 21, 2005 at 07:50:14AM -0600, Kevin Day wrote:

[ .. snip .. ]

> 
> 1) IPv6 on the internet overall seems a bit unreliable at the moment.  
> Entire /32's disappear and reappear, gone for days at a time. The  
> most common path over IPv6 from the US to Europe is US->JP->US->EU. I  
> realize this may be specific to our connection itself, but browsing  
> looking glasses seems to back up that it's not just us.

That really depends on who you are using for an upstream.

There are already *several* sane v6 networks in US who have proper
routing and high-quality US-Europe inter-connections, including
commercial networks that one can purchase transit from.

Networks that still implement legacy 6bone routing practice will find
themselves using scenic routes (i.e. US-JP-US-EU).

[ .. snip .. ]

> 
> 10) Smaller than normal MTUs seem much more common on IPv6, and it is  
> exposing PMTUD breakage on a lot of people's networks.

This is almost all the time due to people misconfiguring their tunnels.
Popular vendors' routers tend to automatically derive tunnel payload
MTU based from physical circuit MTU instead of a 'commonly accepted'
size.

We had problems where a tunneled peer has SONET interface on their side,
basing a tunnel MTU out of 4470, while our side is manually set to 1480
for ipip tunnel.  This causes problem with pmtud.

As outlined in C&W's v6 presentation[1], tunnel MTUs should be explicitly
configured wherever possible.

[1]: http://www.nanog.org/mtg-0505/steinegger.html

[ .. snip .. ]

> 
> I'm also personally a bit concerned with how IPv6 allocation and  
> routing works with respect to small to medium sized networks like  
> ours. I know this is still a hot topic and several proposals are  
> being passed around to resolve some of these issues, but it seems  
> like I *lose* functionality with IPv6 that I have with IPv4, mostly  
> due to the "don't deaggregate your allocation" mantra, and how far  
> the bar was raised to get PI space.  We do a lot of things things in  
> IPv4 land with regard to routing and addressing that I don't believe  
> we can do in IPv6, which worries me more. Shim6 and other proposals  
> are creative, but don't replace a lot of the functionality I'd be  
> losing. This is another story though, that is getting really off topic.
> 

I agree.. but this opens up the whole "Great Multihoming Debate" ;>

James




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