IS-IS Protocol Addresses
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IS-IS (Intermediate System to Intermediate System) Protocol uses NSAP (Network Service Access Point) addresses instead of IP addresses. NSAP addresses consist of an area address, system ID, and N-selector. The area address contains an AFI, IDI, and HODSP. NSAP addresses can also be divided into an interdomain part containing an AFI and IDI, and a domain-specific part containing HODSP, system ID, and NSEL. IS-IS uses different multicast addresses for L1 and L2 updates depending on the network type.
IS-IS Protocol Addresses
- 2. IS-IS (Intermediate System to Intermediate System) Protocol was developed as a OSI network protocol, not TCP/IP. So, normally IS-IS Protocol not uses IP address, but it uses NET (Network EntityTitle) addresses. In IS-IS Protocol, NSAP (Network Service Access Point) is used as network layer address. These addresses are assigned per node, not per interface. And SNPA (Subnetwork Point of Attachment) is the Layer 2 addresses for IS-IS Protocol.
- 3. NSAP consist of three parts. These are: - Area-address -System ID - N-Selector Area address also has some parts inside it.These parts are AFI,IDI and HODSP.
- 4. In previous slide, we have checked an example ISIS address, 49.0115.125a.ab44.1234.11111.0123.abcd.aaaa.00. AS you can see, 49 is the AFI. 0115.125a.ab44.1234 is the IDI part. For Area Address, last part is HODSP and its value is 1111. System ID part of this example address is 0123.abcd.aaaa and the last part SEL part is 00.
- 5. We can also divide the NSAP address into two parts as (1) Inter Domain Part and (2)Domain Specific Part. 1. Inter Domain Part consists of AFI (Authority and Format ID) and IDI (Inter Domain ID). 2. Domain Specific Part consists of High Order Domain Specific Part, System ID and NSEL part. Here, High Order DSP is the subnet, System ID is the identifier of the device in area and the NSEL is the service identifier of NSAP address. When NSEL is equal to “00”, it is called Network Entity Title (NET) and it shows the device itself. NETs are 8 to 20 bytes long. But in general, they are 10 bytes long. System ID can be thought like OSPF Router ID. NSEL is like port/socket inTCP / IP.
- 6. You need to request an official NSAP prefix if you will use CLNS routing. Even if you will need only IP routing when using IS-IS Protocol, you always needs to use NSAP addresses, but this time you can add the private address space AFI 49. AFI 49 is used as local addresses. This addresses are not advertised outside of CLNS network. In IS-IS ProtocolL2 Multicast Addresses are also used. And LSPs are sent to these addresses. In a broadcast network, L1 updates are sent to 0180:C200:0014 and L2 updates are sent to0180:C200:0015. In Point-to-Point networks 0900:2b00:0005 address is used as L2 address.