[v4tov6transition] IPv6 VPNs configured over 1280 MTU tunnels

"Templin, Fred L" <Fred.L.Templin@boeing.com> Fri, 08 October 2010 17:16 UTC

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From: "Templin, Fred L" <Fred.L.Templin@boeing.com>
To: Softwires <softwires@ietf.org>, "v4tov6transition@ietf.org" <v4tov6transition@ietf.org>
Date: Fri, 8 Oct 2010 10:17:40 -0700
Thread-Topic: IPv6 VPNs configured over 1280 MTU tunnels
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Subject: [v4tov6transition] IPv6 VPNs configured over 1280 MTU tunnels
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End systems in end user networks that connect to the
IPv6 Internet will likely want to configure IPv6 VPNs,
e.g., so that they can securely connect to their home
office networks. Those VPN links must present a 1280
minimum MTU to upper layers, but if they traverse a
link in the path with a too-small MTU then the end
system will see an MTU underrun and will need to use
IPv6 fragmentation.

An IPv6-in-IPv4 tunnel with a fixed static 1280 MTU is
an example of a link in the path that could cause such
an MTU underrun for end system VPN links. So, should we
be concerned that tunnels with a fixed 1280 MTU would
make life difficult for the common operational practice
of end systems using VPNs?

Thanks - Fred

> -----Original Message-----
> From: v4tov6transition-bounces@ietf.org 
> [mailto:v4tov6transition-bounces@ietf.org] On Behalf Of 
> Templin, Fred L
> Sent: Friday, October 08, 2010 7:52 AM
> To: Yiu L. Lee; Brian E Carpenter; Ole Troan
> Cc: Softwires; v4tov6transition@ietf.org
> Subject: Re: [v4tov6transition] [Softwires] ISP support of 
> NativeIPv6across NAT44 CPEs -Proposed 6a44 Specification
> > CPE. This double tunneling tech seems scary.
> More to this point about double-tunneling, how were
> folks thinking that IPv6 VPNs would be run over a
> 1280 MTU IPv6-in-IPv4 tunnel? That is double-tunneling,
> and seems like it would be a quite common case, but the
> MTU seems deficient. Should it use IPv6 fragmentation?
> Fred
> fred.l.templin@boeing.com
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