4. プロトコル要求

   As discussed in section 1, IPv6 nodes are not required to implement
   Path MTU Discovery.  The requirements in this section apply only to
   those implementations that include Path MTU Discovery.

1. 序論で議論したように、IPv6ノードは経路MTUの実装を要求されない。当章での要求は、経路MTU探索を含む実装にのみ適用されるものである。

   When a node receives a Packet Too Big message, it MUST reduce its
   estimate of the PMTU for the relevant path, based on the value of the
   MTU field in the message.  The precise behavior of a node in this
   circumstance is not specified, since different applications may have
   different requirements, and since different implementation
   architectures may favor different strategies.


   After receiving a Packet Too Big message, a node MUST attempt to
   avoid eliciting more such messages in the near future.  The node MUST
   reduce the size of the packets it is sending along the path.  Using a
   PMTU estimate larger than the IPv6 minimum link MTU may continue to
   elicit Packet Too Big messages.  Since each of these messages (and
   the dropped packets they respond to) consume network resources, the
   node MUST force the Path MTU Discovery process to end.


   Nodes using Path MTU Discovery MUST detect decreases in PMTU as fast
   as possible.  Nodes MAY detect increases in PMTU, but because doing
   so requires sending packets larger than the current estimated PMTU,
   and because the likelihood is that the PMTU will not have increased,
   this MUST be done at infrequent intervals.  An attempt to detect an
   increase (by sending a packet larger than the current estimate) MUST
   NOT be done less than 5 minutes after a Packet Too Big message has
   been received for the given path.  The recommended setting for this
   timer is twice its minimum value (10 minutes).

経路MTU探索を用いるノードは、可能な限り早くPMTUの減少を検出しなければならない(MUST)。ノードはPMTUの増加を検出するかもしれない(MAY)が、現在の概算PMTUよりも大きなパケットの送信を要求するため、且つPMTUが増えることはないとの見込みのため、これは稀な間隔で行われなければならない(MUST)。(現在の概算より大きなパケットを送信することによる)増加の検出の試みは、与えられた経路にてパケット過大メッセージが受信された後、5分以内に行われてはならない(MUST NOT)。このタイマの推奨される設定は、その最小値の2倍(10分)である。

   A node MUST NOT reduce its estimate of the Path MTU below the IPv6
   minimum link MTU.

ノードは、IPv6最小リンクMTUより小さい経路MTUの概算を減らしてはならない(MUST NOT)。

      Note: A node may receive a Packet Too Big message reporting a
      next-hop MTU that is less than the IPv6 minimum link MTU.  In that
      case, the node is not required to reduce the size of subsequent
      packets sent on the path to less than the IPv6 minimun link MTU,
      but rather must include a Fragment header in those packets [IPv6-


   A node MUST NOT increase its estimate of the Path MTU in response to
   the contents of a Packet Too Big message.  A message purporting to
   announce an increase in the Path MTU might be a stale packet that has
   been floating around in the network, a false packet injected as part
   of a denial-of-service attack, or the result of having multiple paths
   to the destination, each with a different PMTU.

ノードは、パケット過大メッセージの内容への応答に経路MTUの概算を増加してはならない(MUST NOT)。経路MTUの増加通知とのメッセージは、ネットワーク上を古いパケットかもしれないし、サービス不能攻撃の一部として発生する偽造パケットかもしれないし、異なるPMTUをそれぞれがもつ宛先への複数の経路の結果かもしれないからである。


Copyright (C) 2006 七鍵 key@do.ai 初版:2006年10月30日 最終更新:2006年10月30日