rfc1362.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                           M. Allen
Request for Comments: 1362                                  Novell, Inc.
                                                          September 1992


               Novell IPX Over Various WAN Media (IPXWAN)

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard.  Distribution of this memo is
   unlimited.

Abstract

   This document describes how Novell IPX operates over various WAN
   media.  Specifically, it describes the common "IPX WAN" protocol
   Novell uses to exchange necessary router to router information prior
   to exchanging standard IPX routing information and traffic over WAN
   datalinks.

Table of Contents

   1.  Introduction .................................................  1
   1.1. Operation Over PPP ..........................................  2
   1.2. Operation Over X.25 Switched Virtual Circuits ...............  2
   1.3. Operation Over X.25 Permanent Virtual Circuits ..............  2
   1.4. Operation Over Frame Relay ..................................  3
   1.5. Operation Over Other WAN Media ..............................  3
   2.  Glossary Of Terms ............................................  3
   3.  IPX WAN Protocol Description .................................  4
   4.  Information Exchange Packet Formats ..........................  5
   4.1. Timer Request Packet ........................................  6
   4.2. Timer Response Packet .......................................  8
   4.3. Information Request Packet .................................. 10
   4.4. Information Response Packet ................................. 12
   5.  References ................................................... 12
   6.  Security Considerations ...................................... 13
   7.  Author's Address.............................................. 13

1. Introduction

   This document describes how Novell IPX operates over various WAN
   media. It is strongly motivated by a desire for IPX to treat ALL wide
   area links in the same manner. Sections 3 and 4 describe this common
   "IPX WAN" protocol.





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RFC 1362                         IPXWAN                   September 1992


   IPX WAN protocol operation begins immediately after link
   establishment. While IPX is a connectionless datagram protocol, WANs
   are often connection-oriented.  Different WANs have different methods
   of link establishment. The subsections of section 1 of this document
   describe what link establishment means to IPX for different media.
   They also describe other WAN-media-dependent aspects of IPX
   operation, such as protocol identification, frame encapsulation, and
   link tear down.

1.1 Operation Over PPP

   IPX uses PPP [1] when operating over point-to-point synchronous and
   asynchronous networks.

   With PPP, link establishment means the IPX NCP [4] reaches the Open
   state. NetWare IPX will reject all NCP options, and uses normal frame
   encapsulation as defined by PPP. The IPXWAN protocol MUST NOT occur
   until the IPX NCP reaches the Open state.

   PPP allows either side of a connection to stop forwarding IPX if one
   end sends an IPXCP or an LCP Terminate-Request. When a router detects
   this, it will immediately reflect the lost connectivity in its
   routing information database instead of naturally aging it out.

1.2 Operation over X.25 Switched Virtual Circuits

   With X.25, link establishment means successfully opening an X.25
   virtual circuit.  As specified in RFC-1356, "Multiprotocol
   Interconnect on X.25 and ISDN in the Packet Mode" [2], the protocol
   identifier 0x800000008137 is used in the X.25 Call User Data field of
   the Call Request frame, and indicates that the virtual circuit will
   be devoted to IPX.

   Furthermore, each IPX packet is encapsulated directly in X.25 data
   frame sequences without additional framing.

   Either side of the virtual circuit may close it, thereby tearing down
   the IPX link. When a router detects this, it will immediately reflect
   the lost connectivity in its routing information database instead of
   naturally aging it out.

1.3 Operation over X.25 Permanent Virtual Circuits

   The nature of X.25 PVC's is that no call request is made.  When the
   router is informed that X.25 Layer 2 is up, the router should assume
   that link establishment is complete.





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RFC 1362                         IPXWAN                   September 1992


   Each IPX packet is encapsulated in an X.25 data frame sequence
   without additional framing. Novell IPX assumes a particular X.25
   permanent circuit is devoted to the use of IPX.

   If a router receives a layer 2 error condition (e.g., X.25 Restart),
   it should reflect lost connectivity for the permanent circuits in its
   routing information database and re-perform the necessary steps to
   obtain a full IPX connection.

1.4 Operation over Frame Relay

   Novell conforms to RFC-1294, "Multiprotocol Interconnect over Frame
   Relay" [3] for frame relay service and packet encapsulation.
   Currently, Novell has not stabilized the method for treating frame
   relay connections - whether they treat the connections as LANs or
   WANs.

1.5 Operation over other WAN media

   Additional WAN media will be added here as specifications are
   developed.

2. Glossary Of Terms

Primary Network Number:

      Every IPX WAN router has a "primary network number". This is an
      IPX network number unique to the entire internet.  This number
      will be a permanently assigned network number for the router.
      Those readers familiar with NetWare 3.x servers should realize
      that this is the "Internal" network number.

Router Name:

      Every IPX WAN router must have a "Router Name". This is a symbolic
      name given to the router. Its purpose is to allow routers to know
      who they are connected to after link establishment - particularly
      for network management purposes.  A symbolic name conveys more
      information to an operator than a set of numbers. The symbolic
      name should be between 1 and 47 characters in length containing
      the characters 'A' through 'Z', underscore (_), hyphen (-) and
      "at" sign (@). The string of characters should be followed by a
      null character (byte of zero) and padded to 48 characters using
      the null character.  Those readers familiar with NetWare 3.x
      servers should realize that the file server name is the Router
      Name.





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RFC 1362                         IPXWAN                   September 1992


3. IPX WAN Protocol Description

   IPX WAN links have the concept of a LINK MASTER and a LINK SLAVE.
   This relationship is decided upon based on information contained
   within the first IPX packets transferred across the WAN link.

   After link establishment, both sides of the link send "Timer Request"
   packets and start a timer waiting for a "Timer Response". These
   "Timer Request" packets are sent every 20 seconds until a response is
   received or a time-out occurs trying to initialize a connection (the
   timer is restarted each time a new "Timer Request" is sent). The
   time-out should be configurable, and is normally about one minute.
   This is directly dependent on the call setup time for the connection.
   If a time-out occurs, the router issues a disconnect on the offending
   connection and optionally attempts to retry the connection.

   When a "Timer Request" is received, the router with the lowest
   primary network number MUST respond with a "Timer Response" packet -
   and become the "Slave" of the link. If the "Slave" determines that it
   cannot support any of the Routing Types included in the "Timer
   Request" packet, the "Slave" should issue a disconnect on the
   connection being established. The "Master" of the link (determined
   when a "Timer Response" packet is received) is responsible for
   defining the network number that is to be used as a common network
   number for the new WAN link, and for calculating the RIP transport
   time that will be advertized to other RIP routers for the new link.
   This is calculated by stopping the timer which was started when a
   "Timer Request" was initiated and applying the algorithm in section
   4.2.

   To allow this, both sides of the link MUST have an adequate pool of
   WAN network numbers (unique within the internetwork) available to be
   assigned to the link when the call is fully completed. The "Master"
   of the link MUST then select a network number and construct an
   "Information Request" packet containing the calculated link delay,
   the common network number, and its own router name. On receiving this
   packet, the "Slave" MUST turn the packet around, overwrite the router
   name and node identifier and send an "Information Response".

   After the "Master" has received the "Information Response" and the
   "Slave" has received the "Information Request", standard IPX RIP and
   SAP packets are transferred across the WAN link, as currently defined
   for LAN links. The "IPX Router Specification" [5] contains
   information describing the Novell RIP/SAP protocol for third party
   developers.

   Note that the "Information Request" and "Information Response"
   packets are specific to the "Routing Type"=0 information exchanges.



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RFC 1362                         IPXWAN                   September 1992


   With this routing type, no retransmission is made of any of the
   Information packets. If a response has not been received within the
   predefined time-out period, a disconnect is issued on the link, and
   the link can optionally be attempted later.

   If a router detects an error for which no suitable protocol response
   exists (e.g., unable to allocate a network number), the link should
   be terminated according to the relevant media specification.

   Under certain circumstances, particularly on X.25 permanent circuits,
   it is only possible to detect the remote router went away when it
   comes back up again.  In this case, one side of the link receives a
   Timer Request packet when IPX is in a fully connected state.  The
   side receiving the Timer Request MUST realize that a problem
   occurred, and revert to the IPX link establishment phase.
   Furthermore, the routing information learned from this connection
   should be immediately discarded.

4. Information Exchange Packet Formats

   All IPX WAN information exchange packets conform to the standard
   Novell IPX packet format. The packets use the IPX defined packet type
   04 defining a Packet Exchange Packet. The socket number 0x9004 is a
   Novell reserved socket number for exclusive use with IPX WAN
   information exchange. IPX defines that a network number of 0 is
   interpreted as being a local network of unknown number that requires
   no routing. This feature is of use to us in transferring these
   packets before the common network number is exchanged. Some routers
   need to know a "Node Number" (or MAC address) for each node on a
   link. Node numbers will be formed from the "WNode ID" field.  The
   node number will be the 4 bytes of WNode ID followed by 2 bytes of
   zero.

   Router Type number assignment. Other vendors IPX routing protocols
   can make use of the IPXWAN protocol definition by obtaining Router
   Types from Novell. This document will then include the new Router
   Types (with the references to vendor protocol description documents).

   WOption Number assignment. These numbers only need to be assigned
   from Novell for the "Timer Request" and "Timer Response" packets.
   Other packet types (e.g., the "Information Request" packets, are
   dependent on the "Router Type" negotiated and can contain any (vendor
   defined) packet type other than 0 or 1. WOption numbers in these
   packets are then defined by the vendor defining the Routing Type. The
   same packet format should still be maintained.






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RFC 1362                         IPXWAN                   September 1992


4.1 Timer Request Packet

   +---------------------------------------------------------------+
   | Checksum         | FF FF             | Always FFFF            |
   | Packet Length    | 02 40             | Max IPX size (576 bytes|
   |                  |                   | Hi Lo order)           |
   | Trans Control    | 00                | Hops traversed         |
   | Packet Type      | 04                | Packet Exchange Packet |
   | Dest Net #       | 00 00 00 00       | Local Network          |
   | Dest Node #      | FF FF FF FF FF FF | Broadcast              |
   | Dest Socket #    | 90 04             | Reserved WAN socket    |
   | Source Net #     | 00 00 00 00       | Local Network          |
   | Source Node #    | 00 00 00 00 00 00 | Set to zero            |
   | Source Socket #  | 90 04             | Reserved WAN socket    |
   |------------------+-------------------+------------------------|
   | WIdentifier      | 57 41 53 4D       | Confidence identifier  |
   | WPacket Type     | 00                | Timer Request          |
   | WNode ID         | xx xx xx xx       | Primary Net # of       |
   |                  |                   | sending router         |
   |                  |                   | (Hi Lo order)          |
   | WSequence #      | xx                | Sequence start at 0    |
   | WNum Options     | 02                | 2 Options follow       |
   | WOption Number   | 00                | Define Routing Type    |
   | WAccept Option   | 01                | 0=No,1=Yes,3=Not Applic|
   | WOption Data Len | 00 01             | Option length (Hi Lo)  |
   | WOption Data     | 00                | IPX RIP/SAP Routing    |
   | WOption Number   | FF                | Pad option             |
   | WAccept Option   | 01                | 0=No,1=Yes,3=Not Applic|
   | WOption Data Len | 02 0E             | Pad data length (Hi Lo)|
   | WOption Data     | 00->FF's          | Repeated sequence of 00|
   |                  |                   | through FF's.          |
   +---------------------------------------------------------------+

   Note:
        Timer Request packets will always be 576 bytes. However,
        there should be no assumption made about the number of
        options specified in this packet.

   After link establishment, Timer Request packets are sent by both
   sides of the link. Each end starts their sequence number at zero.
   Subsequent retries (every 20 seconds) will increment the value of
   this sequence number.  Only a Timer Response packet with a sequence
   number matching the last sent sequence number will be acted upon.

   When receiving this packet, the WNode ID should be compared to the
   receiver's Primary Network #. If the WNode ID is larger than the
   receiver's Primary Network #, a Timer Response packet should be sent,
   and the receiver should become the link "Slave".



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RFC 1362                         IPXWAN                   September 1992


   Packets received on the reserved socket number not having the
   WIdentifier set to the hexadecimal values noted above should be
   discarded.

Routing Type Option:

   A routing type of zero (0) is the minimum interoperability
   requirement (as defined by this document). A router ready to send a
   Timer Response (and receiving a routing type of zero) MUST respond
   with a routing type of zero. A router ready to send a Timer Response
   (and receiving routing types not matching a supported value) SHOULD
   respond with a Routing Type of zero indicating support for the
   minimum common protocol.

   Note that multiple Routing Type Options can be included in the Timer
   Request packet if the router supports multiple routing methods for
   IPX. The included Router Types MUST include and support this type
   zero option.

Accept Option (for Routing Type and PAD options):

   This field MUST be set to YES if the option is supported, and NO if
   an option is not supported. A Timer Response MUST respond with ONLY
   one Router Type set to YES.