Differences between current version and previous revision of ISIS.
Other diffs: Previous Major Revision, Previous Author, or view the Annotated Edit History
| Newer page: | version 11 | Last edited on Sunday, August 22, 2004 12:25:43 pm | by LindsayDruett | |
| Older page: | version 10 | Last edited on Sunday, August 22, 2004 11:20:08 am | by LindsayDruett | Revert |
@@ -80,8 +80,52 @@
*__DSP__ - Domain Specific Part. The DSP is used to route within the autonomous system. The authority specified by the IDP may further subdivide the DSP and may assign subauthorities responsible for parts of the DSP.
**__High Order DSP__ - High Order DSP is typically the area within the autonomous system.
**__System ID__ - System ID can have a value between 1 and 8 octets. It must have the same length throughout all systems in the autonomous system. Cisco for example uses 6 octets, which is a common solution because it allows the use of the MAC Address to autoconfigure the system.
**__NSEL__ - NSEL is one byte and identifies the particular service at the network layer to which to hand the packet.
+
+!!NETs and NSAPs
+
+NETs and NSAPs are both ISO Addresses. There is a subtle difference between the two.
+
+The NET (Network Entity Title) address is the address of the host, where the value in the NSEL field is set to 0x00. Therefore there is no upper-layer protocol identified within the host. With no application identified with the end host, the packet can be routed to the destination, but it cannot be handed off to a process after it has been delivered. However, routers do not have upper-layer protocols to identify because they are transitory ISs. Therefore, the NSAP of the router is referred to as a Network Entity Title because the NSEL field is set to 00.
+
+The NSAP (Network Service Access Point) is the full ISO address. It not only defines the area and destination host within the area, but also specifies where to send the incoming packet after it has reached the host. The NSEL field at the end of the ISO address specifies the upper-layer protocol and is similar to the Protocol field of the IP header.
+
+!!Rules of ISO Addressing
+
+*The ISO address is assigned to the system, not to the interface.
+*Typically, the router has one NET address. ''There are exceptions to this rule''
+*If multiple NETs ''are'' configured on the same router, they __must__ have the same system ID.
+*The area address must be the same for all routers in the same area.
+*All Level 2 routers must have a system ID that is unique for the entire domain.
+*All level 1 routers must have a system ID that is unique for the entire area.
+*The system ID must be the same length for all ISs and ESs with in a routing domain.
+
+!!Examples of a NET Address...
+
+
+A simple OSI NET Address using a MAC Address...
+
+ 49.0002.0003.6b3c.1e44.00
+
+|AFI ''(Area ID)''|IDI ''(Area ID)''|HO-DSP ''(Area ID)''|System ID|SEL
+|49.| |0002.|0003.6b3c.1e44.|00
+
+
+A simple OSI NET Address using an IP Address (say 10.100.200.254)...
+
+ 49.0001.0101.0020.0254.00
+
+|AFI ''(Area ID)''|IDI ''(Area ID)''|HO-DSP ''(Area ID)''|System ID|SEL
+|49.| |0001.|0101.0020.0254.|00
+
+
+A GOSIP version 2 address, showing the external routing information...
+
+ 49.0001.e09a.e900.0000.0001.0003.6b3c.1e44.00
+
+|AFI ''(Area ID)''|IDI ''(Area ID)''|HO-DSP ''(Area ID)''|System ID|SEL
+|49.|0001.e09a.e900.0000.|0002.|0003.6b3c.1e44.|00
----
!!IS-IS Terms
|Adjacency|Local routing information that shows the reachability of a directly connect End System (ES)- Node or Intermediate System (IS) - Router. A separate adjacency is created for each neighbor on a circuit, and for each level of routing (that is Level 1 and Level 2) on a broadcast circuit.
