CCNP Routing and Switching
- By Scott Empson
- Dec 7, 2007
This chapter is from the book
Rules for Creating a NET
- The NET must begin with a single octet.
- Addresses starting with 49 (AF I= 49) are considered private IP address, analogous to RFC 1918.
- — Routed by IS-IS
- — Should not be advertised to other Connectionless Network Service (CLNS) networks (outside this IS-IS domain)
- Additional 2 bytes added for the area ID.
- All routers in the same area must have the same area address.
- The system ID must be the same number of octets throughout the domain.
- Cisco has implemented a fixed length of 6 octets for the system ID of a NET.
- It is customary to use the MAC address of the router, or an IP address of a loopback interface (192.168.111.3 = 192.168.111.003 = 1921.6811.1003).
- The practice of using a modified loopback IP address as the system ID may now be considered outdated because of the dynamic host name feature. This feature uses a new Type Length Value (TLV 137) to map the router's host name to the system ID.
- Each device must have a unique system ID within the area.
- The NET must end with a single octet—the network service access point (NSAP) selector byte (NSEL), usually set to 0x00.
- — When the NSEL is set to 0, it identifies the device itself.
- — The NSEL is like a TCP port number: It indicates the transport layer.