SAP, Service Advertising Protocol

Description Glossary RFCs Publications Obsolete RFCs

Description:

Protocol suite:Novell NetWare.
Protocol type:Application layer protocol.
Socket:0x452

SAP is a Novell NetWare protocol which is used for service providers to advertise their services on the network.

RFC 1582, page 20:

Netware [Novell Incorporated, "IPX Router Specification", Version 1.10, October 1992.] supports a mechanism that allows servers on an internetwork to advertise their services by name and type using the Service Advertising Protocol (SAP) which runs over the Internetwork Packet Exchange (IPX) protocol using socket number 452h.

SAP operates on similar principals to running RIP. Routers act as SAP agents, collecting service information from different networks and relay it to interested parties.

To support the triggered update mechanism outlined in this proposal the packet format for Netware SAP is modified.

RFC 1582, pages 1 and 2:

Routing information is sent on the WAN when the routing database is modified by new routing information received from another interface. When this happens a (triggered) update is sent to a list of destinations on other WAN interfaces. Because routing protocols are datagram based they are not guaranteed to be received by the peer router on the WAN. An acknowledgement and retransmission mechanism is provided to ensure that routing updates are received.

The WAN circuit manager advises the routing applications on the reachability and non-reachability of destinations on the WAN.

RFC 2091, pages 3 and 4:

Periodic broadcasting by Bellman-Ford (distance vector) algorithm information broadcasting protocols IP RIP, IP RIP V2 or Netware RIP and SAP generally prevents WAN circuits from being closed. Even on fixed point-to-point links the overhead of periodic transmission of RIP - and even more so SAP broadcasts - can seriously interrupt normal data transfer simply through the quantity of information which hits the line every 30 or 60 seconds.

To overcome these limitations, this specification modifies the distance vector protocols so as to send information on the WAN only when there has been an update to the routing database OR a change in the reachability of a next hop router is indicated by the task which manages connections on the WAN.

Because datagrams are not guaranteed to get through on all WAN media, an acknowledgement and retransmission system is required to provide reliability.

The protocols run unmodified on Local Area Networks (LANs) and so interoperate transparently with implementations adhering to the original specifications.

Multiprotocol routers are used on connection oriented Wide Area Networks (WANs), such as X.25 packet switched networks and ISDN networks, to interconnect LANs. By using the multiplexing properties of the underlying WAN technology, several LANs can be interconnected simultaneously through a single physical interface on the router. A circuit manager provides an interface between the connectionless network layers, IP and IPX, and the connection oriented WAN, X.25, ISDN etc.

RFC 2091, page 12:

To support the mechanism outlined in this proposal the packet format for Novell SAP is modified when using Operations Update Request (9), Update Response (10) and Update Acknowledge (11).


MAC header IPX header SAP packet

SAP Service Query Packet format:

00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15
Packet Type
Server Type

Packet Type. 16 bits.
General service query or nearest service query.

Server Type. 16 bits.
The type of service requested.


SAP Service Response Packet format:

00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15
Packet Type
Server Type
Server Name :::
Network Address
Node Address

Socket Address
Network Hops

Packet Type.. 16 bits.

ValueDescriptionReferences
1 General service query.  
2 General service response.  
3 Nearest service query.  
4 Nearest service response.  
6 Triggered general service query. A request for the responding system to send the identities of all servers of all types. RFC 1582
7 Triggered general service response. A message containing all of the sender's services table, excluding those entries learned from the interface to which the service advertising information is being sent out. RFC 1582
8 Triggered general service acknowledgement. A message sent in response to every triggered general service response packet received. RFC 1582
9 Update request. RFC 2091
10 Update response. RFC 2091
11Update acknowledge. RFC 2091

Server Type. 16 bits.
The type of service available.

Server Name. 48 bytes.
The name of the server.

Network Address. 32 bits.
The network address of the service provider.

Node Address. 48 bits.
The device address of the service provider.

Socket Address. 16 bits.
The socket number that identifies a requested service on a device.

Network Hops. 16 bits.
The number of hop counts from a client to a server provider. A hop count is when a packet is forwarded to the next router.


Glossary:


RFCs:

[RFC 1582] Extensions to RIP to Support Demand Circuits.

[RFC 2091] Triggered Extensions to RIP to Support Demand Circuits.


Publications:


Obsolete RFCs:


Description Glossary RFCs Publications Obsolete RFCs