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M. Allen, Novell, Inc.
September 1992
Novell IPX Over Various WAN Media (IPXWAN)
1. Introduction
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.
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. 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.
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.
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.
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.
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".
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.
PAD Option:
This option will normally be the last entry in the packet. Its sole
purpose is to fill the IPX packet to be 576 bytes. The pad option data
will contain a repeating sequence of zero's through 0xFF's. This should
stop compression modems from collapsing the packet and destroying the link
delay calculation.
Currently Assigned WOption Numbers (Timer Request Packet):
Routing Type Option = 0x00; Option Length = 0001
Current option data values:
0 Novell RIP/SAP routing with network
number assigned to the link.
PAD Type Option = 0xFF; Option Length = Variable
Compression Option = 0x80; Option Length = Variable
(length dependent on compression type)
Current option data values:
Byte 1 Compression type
0 = Telebit compression (length=3) [6]
Telebit Byte 2 - Compression options
Telebit Byte 3 - Number compression slots
4.2. Timer Response 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 | 01 | Timer Response |
| WNode ID | xx xx xx xx | Primary Net # of |
| | | sending router |
| | | (Hi Lo order) |
| WSequence # | xx | Same as Timer Request |
| | | received |
| 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 |
| | | (Minimum interoperating|
| | | requirement). Others |
| | | may be defined by at a |
| | | later date by Novell |
| 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 to stop |
| | | compression modems |
| | | doing any compression |
| | | for link delay calc. |
+---------------------------------------------------------------+
The responses contained within this packet are as described in section 4.1.
Any unknown options or not supported options from the Timer Request should
have the WAccept Option set to NO.
If the Timer Request packet contained more than one Router Type option and
the "Slave" supports all the options, the "Slave" should set the WAccept
Option to NO on all Router Types except the Routing
Type which is to be adopted. The "Master" of the link will then adopt the
routing option specified with the YES setting and complete further
information exchanges according to that routing standard.
This packet should contain the same sequence number as the received Timer
Request. This packet should ONLY be sent by the router determining
themselves to be the "Slave" of the link.
Currently Assigned WOption Numbers (Timer Response Packet):
Routing Type Option = 0x00; Option Length = 0001
Current option data values:
0 Novell RIP/SAP routing with network
number assigned to the link.
PAD Type Option = 0xFF; Option Length = Variable
Compression Option = 0x80; Option Length = Variable
(length dependant on compression type)
Current option data values:
Byte 1 Compression type
0 = Telebit compression (length=3) [6]
Telebit Byte 2 - Compression options
Telebit Byte 3 - Number compression slots
4.3. RIP/SAP Information Request Packet (Router Type=0 Only)
+---------------------------------------------------------------+
| Checksum | FF FF | Always FFFF |
| Packet Length | 00 63 | Size of header+data |
| | | (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 | 02 | Information Request |
| WNode ID | xx xx xx xx | Primary Net # of |
| | | sending router |
| | | (Hi Lo order) |
| WSequence # | 00 | Sequence start at 0 |
| WNum Options | 01 | 1 Option to follow |
| WOption Number | 01 | Define IPX RIP/SAP |
| | | info exchange |
| WAccept Option | 01 | 0=No,1=Yes,3=Not Applic|
| WOption Data Len | 00 36 | Option length (Hi Lo) |
| WOption Data | | |
| Link Delay | xx xx | Hi Lo link delay in |
| | | milli seconds (see |
| | | below for calculation) |
| Common Net # | xx xx xx xx | Hi Lo Common Network # |
| Router Name | xx (x 48 decimal) | Router name - as defned|
| | | in section 2. |
+---------------------------------------------------------------+
Calculation of link delay is performed as follows:
// Start_time is a time stamp when Timer Request sent out
// End_time is a time stamp when a Timer Response is
// received.
link_delay = end_time - start_time; // 1/18th second
// We are on a slow net, so add some biasing to help stop
// multiple workstation sessions timing out on the link
if (link_delay < 1)
{
link_delay = 1;
}/*IF*/
link_delay *= 6; // Add the biasing
link_delay *= 55; // Convert link delay to milliseconds
The "Link Delay" is used as the network transport time when advertized in
the IPX RIP packet tuple for the network entry "Common Net #". For a
consistent network, a common link delay is required at both ends of the
link and is calculated by the link "Master".
The Common Net # is supplied by the link "Master". This number must be
unique in the connected internetwork. Each WAN call requires a separate
number.
Currently only a single option is defined for the "Information Request"
packet for Routing Type=0.
4.4. RIP/SAP Information Response Packet (Router Type=0 Only)
+---------------------------------------------------------------+
| Checksum | FF FF | Always FFFF |
| Packet Length | 00 63 | Size of header+data |
| | | (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 | 03 | Information Response |
| WNode ID | xx xx xx xx | Primary Net # of |
| | | sending router |
| | | (Hi Lo order) |
| WSequence # | 00 | Sequence start at 0 |
| WNum Options | 01 | 1 Option to follow |
| WOption Number | 01 | Define IPX RIP/SAP |
| | | info exchange |
| WAccept Option | 01 | 0=No,1=Yes,3=Not Applic|
| WOption Data Len | 00 36 | Option length (Hi Lo) |
| WOption Data | | |
| Link Delay | xx xx | Hi Lo link delay (as |
| | | received in Info Requ) |
| Common Net # | xx xx xx xx | Hi Lo Common Network # |
| | | (as received in Info |
| | | request) |
| Router Name | xx (x 48 decimal) | Router name - as defned|
| | | in section 2. |
+---------------------------------------------------------------+
The responses contained within this packet are as described in
section 4.3.
5. References
[1] Simpson, W., "The Point-to-Point Protocol (PPP) for the Transmission of
Multi-protocol Datagrams over Point-to-Point Links", RFC 1331, May 1992.
[2] Malis, A., Robinson, D., and R. Ullman, "Multiprotocol Interconnect on
X.25 and ISDN in the Packet Mode", RFC 1356, August 1992.
[3] Bradley, T., Brown, C., and A. Malis, "Multiprotocol Interconnect
over Frame Relay", RFC 1294, January 1992.
[4] Simpson, W., "The PPP Internetwork Packet Exchange Control Protocol
(IPXCP) Compromise Version", Work in Progress.
[5] Novell IPX Router Specification. Novell Part Number 107-000029-001.
(Note: Currently, this document is only available as part of a Novell
developers program as part of an SDK. Novell Labs, Provo (UT) should be
able to provide more information on this document.)
[6] Lewis, M., Telebit Corp. "IPX Header Compression based on Van Jacobson
Header Compression for TCP/IP", Work in Progress, contact:
(mlewis@telebit.com).
Author's Address
Michael Allen
Novell, Inc.
2180 Fortune Drive
San Jose, CA 95131
EMail: MALLEN@NOVELL.COM