Masataka,
Thanks for your thoughtful review. Would your concern be addressed if we added
the text below?
Ron
TEXT
====
2.2.1. RFC 2460 Compliance
OLD>
The solution described above is widely-deployed on the Internet in its default
configuration.
<OLD
NEW>
The solution described above is widely-deployed on the Internet in its default
configuration. However, the default configuration is not always appropriate for
GRE tunnels that carry IPv6.
IPv6 requires that every link in the Internet have an MTU of 1280 octets or
greater. On any link that cannot convey a 1280-octet packet in one piece,
link-specific fragmentation and reassembly must be provided at a layer below
IPv6.
Therefore, the default configuration is appropriate for tunnels that carry IPv6
only if the network is engineered so that the GMTU is guaranteed to be
1280-bytes or greater. In all other scenarios, a non-default configuration is
required.
In the non-default configuration, when the GRE ingress router receives a packet
lager than the GMTU, the GRE ingress router encapsulates the entire packet in a
single GRE and delivery header. It then fragments the delivery header and sends
the resulting fragments to the GRE egress, where they are reassembled.
<NEW
-----Original Message-----
From: ietf [mailto:ietf-bounces(_at_)ietf(_dot_)org] On Behalf Of Masataka
Ohta
Sent: Friday, April 10, 2015 8:26 AM
To: ietf(_at_)ietf(_dot_)org
Cc: int-area(_at_)ietf(_dot_)org
Subject: Re: Last Call: <draft-ietf-intarea-gre-mtu-02.txt> (A Widely-
Deployed Solution To The Generic Routing Encapsulation (GRE)
Fragmentation Problem) to Informational RFC
As the draft says;
o When the GRE ingress node receives a non-fragmentable packet with
length greater than the GMTU, it discards the packet and send an
ICMP PTB message to the packet's source.
the draft should clearly state that, if GMTU<1280B, it is a violation of the
following requirement of RFC2460:
IPv6 requires that every link in the internet have an MTU of 1280
octets or greater. On any link that cannot convey a 1280-octet
packet in one piece, link-specific fragmentation and reassembly must
be provided at a layer below IPv6.
and that 1280B IPv6 packets can not be carried over IPv6 with the default GRE
configuration.
It is especially so, because, according to the draft:
Typically, GRE ingress nodes further refine their GMTU estimate by
executing PMTUD procedures. However, if an implementation supports
PMTUD for GRE tunnels, it also includes a configuration option that
disables PMTUD. This configuration option is required to mitigate
certain denial of service attacks (see Section 5).
PMTUD is often turned off and, then, RFC2460 requires GMTU<1280B.
Also, I think the paragraph above is not very honest on the reason why
PMTUD is often turned off.
Masataka Ohta