I believe the text you are referring to is the following:
"When the application is sending packets too big for the path MTU
recvmsg() will return zero (indicating no data) but there will be a
cmsghdr with cmsg_type set to IPV6_PATHMTU, and cmsg_len will
indicate that cmsg_data is sizeof(struct ip6_mtuinfo) bytes long."
The way I read this, applications are informed of path MTU restrictions
when they are actively sending packets that result in ICMPv6 "packet too
big" error messages (i.e., even when the "packet too big" messages are
locally-generated). I see no requirement in this specification for
asynchronous notification of PMTU decreases.
Instead, in RFC 1918, section 5.2, I see:
Note: An implementation can avoid the use of an asynchronous
notification mechanism for PMTU decreases by postponing
notification until the next attempt to send a packet larger than
the PMTU estimate. In this approach, when an attempt is made to
SEND a packet that is larger than the PMTU estimate, the SEND
function should fail and return a suitable error indication. This
approach may be more suitable to a connectionless packetization
layer (such as one using UDP), which (in some implementations) may
be hard to "notify" from the ICMP layer. In this case, the normal
timeout-based retransmission mechanisms would be used to recover
from the dropped packets.
Fred Templin
[EMAIL PROTECTED]
Lilian Fernandes wrote:
Section 11.3 of draft-ietf-ipngwg-rfc2292bis-08 describes a socket option
IPV6_RECVPATHMTU that a UDP application can set to be notified of path MTU
changes.
http://www.ietf.org/internet-drafts/draft-ietf-ipngwg-rfc2292bis-08.txt
-Lilian
On Tue, 7 Jan 2003, Shashi Kumar wrote:
ICMP layer should recalculate the path-MTU depending on ICMP redirect
and update the routing entries appropriately and also inform
packetization layer(s) about the change in path-MTU ( you can have your
own algo.)
-Shashi
Keshava Ayanur wrote:
Hi,
I have a question about PATH-MTU .
Should the IP stack inform the application about the change in
path-MTU .
Else how does the application running on UDP will know about
change in the
size ?
Or is it up to the application running on UDP to care by some
reliable mechanism ?
Regards,
keshava
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Lilian Fernandes
AIX TCP/IP Development - IBM Austin
Tel: 512-838-7966 Fax: 512-838-3509
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