rfc1582.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

   o  A router receiving fragments MUST re-assemble them before
      updating its routing database.

   o  If all fragments are not received within four times the
      retransmit period, they MUST be discarded.

      A triggered request packet MUST then be sent to the originator
      of the routing update.

      On receiving the triggered request packet, the originator of the
      routing update MUST retransmit ALL fragments.

   o  If a fragment with an updated sequence number is received, ALL
      fragments with the earlier sequence number MUST be discarded.

      An updated sequence number is defined as any sequence number
      that is different.  There is no concept of the value of the
      sequence number conveying its age.



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RFC 1582                       Demand RIP                  February 1994


   Fragmentation timer values are covered in section 7.

2.9 Preventing Queue Overload

   In order to prevent too many routing messages being queued at a WAN
   interface, the routing task MAY operate a scheme whereby
   'broadcasting' of a triggered request or triggered response to a WAN
   interface is staggered.  All routing requests or routing responses
   are not sent to ALL next hop routers on the interface in a single
   batch:

   o  The routing task should limit the number of outstanding triggered
      request messages for which a triggered response has not been
      received.

   o  The routing task should limit the number of outstanding triggered
      response messages for which a triggered acknowledgement has not
      been received.

   As outstanding messages are appropriately acknowledged, further
   messages can be sent out to other next hop routers, until all next
   hop routers have been sent the message and have acknowledged it.

   The maximum number of outstanding messages transmitted without
   acknowledgement is a function of the link speed and the number of
   other routing protocols operating the triggered update mechanism.

   Messages should always be acknowledged immediately (even if it causes
   the limit to be exceeded), since a connection is almost certainly
   available.  This has the potential benefit of allowing the VC to
   close sooner (on its idle timer).

   Sending all triggered request fragments to a destination at once is
   also beneficial.

3. IP Routing Information Protocol Version 1

   This section should be read in conjunction with reference [1].

   IP RIP is a UDP-based protocol which generally sends and receives
   datagrams on UDP port number 520.

   To support the mechanism outlined in this proposal the packet format
   for RIP version 1 [1] is modified as shown in Figure 2.

   Every Routing Information Protocol datagram contains the following:





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RFC 1582                       Demand RIP                  February 1994


   COMMAND   Commands supported in RIP Version 1 are: request (1),
             response (2), traceon (3), traceoff (4), SUN reserved (5).
             The fields sequence number, fragment number and number of
             fragments MUST NOT be included in packets with these
             command values.

             The following new commands (with values in brackets) are
             required:

       TRIGGERED REQUEST (6)

                 A request for the responding system to send all of its
                 routing database.

                 Only the first 4 octets of the packet format shown in
                 figure 2 are sent, since all routing information is
                 implied by this request type.

       TRIGGERED RESPONSE (7)

                 A message containing all of the sender's routing
                 database, excluding those entries learned from the
                 interface to which the routing information is being
                 sent.

                 This message may be sent in response to a triggered
                 request, or it may be an update message resulting
                 from a change in the routing database.

                 A triggered response message MUST be sent in response
                 to a triggered request message even if there are no
                 routes to propagate.  This would be the case for a
                 host which had a WAN interface only, but which wished
                 to run the triggered update protocol.

     0                   1                   2                   3 3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | command (1)   | version (1)   |      must be zero (2)         |
     +---------------+---------------+-------------------------------+

        The following new fields are inserted for some commands

     0                   1                   2                   3 3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    sequence number (2)        | fragment (1)  |no of frags (1)|
     +-------------------------------+-------------------------------+



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RFC 1582                       Demand RIP                  February 1994


          Followed by up to 25 routing entries (each 20 octets)

     0                   1                   2                   3 3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | address family identifier (2) |      must be zero (2)         |
     +-------------------------------+-------------------------------+
     |                         IP address (4)                        |
     +---------------------------------------------------------------+
     |                        must be zero (4)                       |
     +---------------------------------------------------------------+
     |                        must be zero (4)                       |
     +---------------------------------------------------------------+
     |                          metric (4)                           |
     +---------------------------------------------------------------+
                                     .
                                     .

     The format of an IP RIP datagram in octets, with each tick mark
     representing one bit.    All fields are in network order.

     The four octets: sequence number (2), fragment number (1) and
     number of fragments (1) are not present in the original RIP
     specification.  They are only present if command takes the
     values 7 or 8.


          Figure 2.   IP Routing Information Protocol packet format


       TRIGGERED ACKNOWLEDGEMENT (8)

                 A message sent in response to every triggered response
                 packet received.

                 Only the first 8 octets of the packet format shown in
                 figure 2 are sent.

   VERSION   In this instance Version 1.

   SEQUENCE NUMBER

             This is a new field inserted if command takes the values 7
             or 8.

             The sequence number MUST be incremented every time updated
             information is sent out on a WAN.  The sequence number
             wraps round at 65535.



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RFC 1582                       Demand RIP                  February 1994


             When a triggered acknowledgement is sent the sequence
             number is set to the same value as the triggered response
             packet being acknowledged.

             The sequence number MUST be identical over fragments.  If a
             fragment is retransmitted the sequence number MUST not
             change.

   FRAGMENT NUMBER

             The fragment number is one for the first fragment of a
             routing update, and is incremented for each subsequent
             fragment.  A fragment can contain up to 25 routing entries.

             When a triggered acknowledgement is sent the fragment
             number is set to the same value as the triggered response
             packet being acknowledged.

   NUMBER OF FRAGMENTS

             In a triggered response packet this indicates the number of
             packets required to complete the routing update.

             This field has no relevance for triggered acknowledgement
             packets so should be set to zero.

   For triggered response packets the rest of the datagram contains a
   list of destinations, with information about each.  Each entry in
   this list contains the address family identifier (2 for IP), a
   destination network or host, and the metric for it.  The packet
   format is intended to allow RIP to carry routing information for
   several different protocols, identifiable by the family identifier.

   The IP address is the usual Internet address, stored as 4 octets in
   network order.  The metric field contains a value between 1 and 15
   inclusive, specifying the current metric for the destination, or the
   value 16 (representing 'infinity'), which indicates that the
   destination is not reachable.  Each route sent by a router supersedes
   any previous route to the same destination from the same router.

   The maximum datagram size is 508 octets, excluding UDP and IP
   headers.

4. IP Routing Information Protocol Version 2

   An enhancement to IP RIP to include subnetting has recently become
   available [2].  This section only describes differences from that
   RFC.



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RFC 1582                       Demand RIP                  February 1994


   The triggered update mechanism can be supported by including the
   triggered request (6), triggered response (7) and triggered
   acknowledgement (8) commands described in the previous section.

   The sequence number, fragment number and number of fragments fields
   are included in triggered response and triggered acknowledgement
   commands.

   The triggered request packet should also contain the 4 extra octets
   corresponding to the sequence number, fragment number and number of
   fragments fields - but set to zero.

   Because additional security information is included in RIP Version 2
   packets, this MUST be appended to the triggered request and triggered
   acknowledgement packets, as well as being present in the triggered
   response packet.

   The version number becomes 2.  Other aspects of packet layout follow
   reference [2].

5. Netware Routing Information Protocol

   This section should be read in conjunction with references [3], since
   it only describes differences from the specification.

   Netware [3] is the trade name of Novell Research's protocols for
   computer communication which are derived and extended from Xerox
   Network System's (XNS) protocols [4].

   Netware supports a mechanism that allows routers on an internetwork
   to exchange routing information using the Routing Information
   Protocol (RIP) which runs over the Internetwork Packet Exchange (IPX)
   protocol using socket number 453h.

   Netware RIP and IP RIP share a common heritage, in that they are both
   based on XNS RIP, but there is some divergence, mostly at the packet
   format level to reflect the differing addressing schemes.

   The triggered update mechanism can be applied to Netware RIP.  To
   support the mechanism outlined in this proposal the packet format for
   Netware RIP is modified as shown in Figure 3.

   Every datagram contains the following:








Meyer                                                          [Page 17]

RFC 1582                       Demand RIP                  February 1994


   RIP OPERATION

             Operations supported in standard Netware RIP are: request
             (1) and response (2).

             The fields sequence number, fragment number and number of
             fragments MUST NOT be included in packets with these
             operation values.

             The following new operations are required (with values
             chosen to be the same as for IP RIP commands):

     0                   1         1
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       operation (2)           |
     +---------------+---------------+

        The following new fields are inserted for some operations