On 16-Nov-00 Erik Nordmark wrote:
>>
>> On 16-Nov-00 JINMEI Tatuya wrote:
>> > Applications can dynamically grab the path MTU by the IPV6_RECVPATHMTU
>> > socket option (upon receiving an ICMPv6 packet toobig error).
>> >
>>
>> Is that mean, when IPV6_RECVPATHMTU option is setted (UDP/raw socket), that
>> fragmentation is disabled ?
>
> No, I don't think so.
> IPV6_RECVPATHMTU is so that e.g. UDP applications that do packetization
> can determine when the path MTU changes and adjust the size of the
> packets they are sending.
>
> Should we just define the semantic equivalent of setting IP_DF on
> a raw socket with IP_HDRINCL set for IPv6? (IPV6_DONTFRAG?)
[ylg]=> Yes, that's exactly wee need, a socket option like :
int on = 1;
setsockopt(fd, IPPROTO_IPV6, IPV6_DONTFRAG, &on, sizeof(&on));
to disable fragmentation for UDP/Raw sockets (and of course on = 0 to
(re)enable fragmentation which would be the default).
> This would allow a traceroute to detect the MTU, and it would allow
> the above UDP example application to avoid "accidental" fragmentation
> by a too helpful IP/UDP layer. (The IP/UDP layer needs to be helpful for
> UDP applications which are not involved in PMTU discovery.)
>
> Erik
As we said in a previous message, F. Dupont and me, a useful option would be a
new option to getsockopt() to get the outgoing MTU. For example, it helps
tracemtu to discover the right mtu to start (otherwise, we have to set
IPV6_DONTFRAG option, and try successive MTU (choosen in a list of possible
MTU, ordered decreasingly) until we don't get EMSGSIZE error (an other pb :
does exist such a list, i.e. the (right) list of all possible MTUs?).
Regards,
----------------------------------
Yves Legrandg�rard
E-Mail: [EMAIL PROTECTED]
Date: 17-Nov-00
Time: 14:24:22
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