NLSP: NetWare Link Services Protocol

The NetWare Link Services Protocol (NLSP) is a link-state routing protocol in the Novell NetWare architecture. NLSP is based on the OSI Intermediate System-to-Intermediate System (IS-IS) protocol and was designed to replace IPX RIP (Routing Information Protocol) and SAP (Service Advertisement Protocol), Novell's original routing protocols that were designed for small scale internetworks.

Compared to RIP and SAP, NLSP provides improved routing, better efficiency, and scalability. The following are the key features of the NLSP:

• NLSP-based routers use a reliable delivery protocol, so delivery is guaranteed.
• NLSP facilitates improved routing decisions because NLSP-based routers store a complete map of the network, not just next-hop information.
• NLSP is efficient, particularly over a WAN link, because its support of IPX header compression makes it possible to reduce the size of packets. NLSP also supports multicast addressing so that routing information is sent only to other NLSP routers, not to all devices, as RIP does.
• NLSP supports load balancing across parallel paths and improves link integrity. It periodically checks links for connectivity and for the data integrity of routing information.
• NLSP is scalabe because NLSP can support up to 127 hops (RIP supports only 15 hops) and permits hierarchical addressing of network nodes, which allows networks to contain thousands of LANs and servers.
• NLSP-based routers are backward compatible with RIP-based routers.

Similar to IS-IS, NLSP supports hierarchical routing with area, domain, and global internetwork components. Areas can be linked to create routing domains, and domains can be linked to create a global internetwork. NLSP supports three levels of hierarchical routing: Level 1, Level 2, and Level 3 routing.

An NLSP router extracts certain information from the adjacency database and adds locally derived information. Using this information, the router constructs a link-state packet (LSP) that describes its immediate neighbors. All LSPs constructed by all routers in the routing area make up the link-state database for the area. The link-state database is synchronized by reliably propagating LSPs throughout the routing area when a router observes a topology change. Two methods ensure that accurate topology-change information is propagated: flooding and receipt confirmation.

• Protocol ID - Identifies the NLSP routing layer with the 0x83 hex number.
• Length indicator - Determines the number of bytes in the fixed portion of the header.
• Minor version - Contains one possible decimal value and is ignored on receipt.
• Reserved - Contains no decimal values and is ignored on receipt.
• Packet type (5 bits) - Contains 17 possible decimal values.
• Major version - Contains one possible decimal value.
• Reserved - Contains no decimal values and is ignored on receipt.
• State (2 bits) - Sends the router's state associated with the link (0 = up, 1 = initializing, 2 = down).
• Circuit type (Cct type) - Consists of 2 bits. This field can have one of the following values:
• 0 - Reserved value; ignore entire packet.
• 1 - Level 1 routing only.
• 2 - Level 2 routing only. (The sender uses this link for Level 2 routing.)
• 3 - Both Level 1 and Level 2. (The sender is a Level 2 router and uses this link for Level 1 and Level 2 traffic.)
• Source ID - Serves as the system identifier of the sending router.
• Holding time - Contains the holding timer, in seconds, to be used for the sending router.
• Packet length - Determines the entire length of the packet, in bytes, including the NLSP header.
• Local WAN circuit ID - Acts as a unique identifier assigned to this circuit when it is created by the router.
• Variable length field - Consists of a series of optional fields.

NLSP LAN Hello Packet:

• Protocol ID - Identifies the NLSP routing layer with the 0x83 hex number.
• Length indicator - Determines the number of bytes in the fixed portion of the header (up to and including the LAN ID field).
• Minor version - Contains one possible decimal value and is ignored on receipt.
• Reserved - Contains no possible decimal values and is ignored on receipt.
• Packet type (5 bits) - Contains 15 possible decimal values.
• Major version - Contains one possible decimal value.
• Reserved - Contains no possible decimal values and is ignored on receipt.
• No multicast (NM) (1 bit) - Indicates, when set to 1, that the packet sender cannot receive traffic addressed to a multicast address. (Future packets on this LAN must be sent to the broadcast address.)
• Circuit type (Cct Type) (2 bits) - Can have one of the following values:
• 0 - Reserved value; ignore entire packet.
• 1 - Level 1 routing only.
• 2 - Level 2 routing only. (The sender uses this link for Level 2 routing.)
• 3 - Both Level 1 and Level 2. (The sender is a Level 2 router and uses this link for Level 1 and Level 2 traffic.)
• Source ID - Contains the system ID of the sending router.
• Holding time - Contains the holding timer, in seconds, to be used for the sending router.
• Packet length - Determines the entire length of the packet, in bytes, including the NLSP header.
• R - Contains no possible decimal values and is ignored on receipt.
• Priority (7 bits) - Serves as the priority associated with being the LAN Level 1 designated router. (Higher numbers have higher priority.)
• LAN ID - Contains the system ID (6 bytes) of the LAN Level 1 designated router, followed by a field assigned by that designated router.
• Variable length fields - Consists of a series of optional fields.

NetWare Link Services Protocol (NLSP) is a Novell protocol