1. IS-IS function introduction:
The Intermediate System to Intermediate System (IS-IS) belongs to the Interior Gateway Protocol (IGP) and is used inside the autonomous system. IS-IS is also a link state protocol, which uses the Shortest Path First (SPF) algorithm for route calculation.
2. IS-IS application scenarios:
In order to support large-scale routing networks, IS-IS adopts a two-level hierarchical structure of backbone area and non-backbone area in the autonomous system. Generally speaking, Level-1 routers are deployed in non-backbone areas, and Level-2 routers and Level-1-2 routers are deployed in backbone areas. Each non-backbone area is connected to the backbone area through a Level-1-2 router.
3. IS-IS router classification:
1. Level-1 router
The Level-1 router is responsible for routing within the area. It only forms a neighbor relationship with Level-1 and Level-1-2 routers belonging to the same area. Level-1 routers belonging to different areas cannot form a neighbor relationship. The Level-1 router is only responsible for maintaining the Level-1 Link State Database (LSDB). The LSDB contains the routing information of the local area, and the packets outside the local area are forwarded to the nearest Level-1-2 router.
2. Level-2 router
1) A Level-2 router is responsible for routing between areas. It can form a neighbor relationship with Level-2 routers in the same or different areas or Level-1-2 routers in other areas. A Level-2 router maintains a Level-2 LSDB, which contains routing information between areas.
2) All Level-2 routers (that is, forming a Level-2 neighbor relationship) form the backbone network of the routing domain and are responsible for communication between different areas. The Level-2 routers in the routing domain must be physically continuous to ensure the continuity of the backbone network. Only Level-2 routers can directly exchange data packets or routing information with routers outside the area.
3. Level-1-2 router
1) A router that belongs to both Level-1 and Level-2 is called a Level-1-2 router. It can form a Level-1 neighbor relationship with Level-1 and Level-1-2 routers in the same area, or with other areas The Level-2 and Level-1-2 routers form a Level-2 neighbor relationship. Level-1 routers must pass through Level-1-2 routers to connect to other areas.
2) The Level-1-2 router maintains two LSDBs, the Level-1 LSDB is used for intra-area routing, and the Level-2 LSDB is used for inter-area routing.
4. IS-IS address structure:
1. Network Service Access Point (NSAP) is the address used to locate resources in the OSI protocol. It is composed of IDP (Initial Domain Part) and DSP (Domain Specific Part). The length of IDP and DSP is variable, the total length of NSAP is 20 bytes at most and 8 bytes at least.
2. The network entity name NET (Network Entity Title) refers to the network layer information of the device itself, which can be regarded as a special type of NSAP (SEL=00). The length of NET is the same as that of NSAP, with a maximum of 20 bytes and a minimum of 8 bytes. When configuring IS-IS on the router, only NET needs to be considered, and NSAP does not need to be concerned.
For example, if NET is: ab.cdef.1234.5678.9abc.00, the Area Address is ab.cdef, the System ID is 1234.5678.9abc, and SEL is 00.
5. IS-IS experimental configuration:
1. Topological diagram
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2. The purpose of the experiment: Configure basic IS-IS functions on each router to achieve network interconnection. Among them, configuring AR1 and AR3 as Level-1 routers can enable these two routers to maintain a relatively small amount of data information
3. Configuration ideas:
1) Set up the topology map environment and mark the planned IP address
2) Modify the default name of the network device and configure the IP address
3) Configure OSPF routing to enable mutual access between network segments
4. Configuration process:
Step 1: Modify the default name of the network device and configure the IP address
1) Configure each PC information (omitted)
2) Configure router AR1 default name and interface IP
<Huawei>sys //Enter system view mode
Enter system view, return user view with Ctrl+Z.
[Huawei]sysname AR1 //Modify the name of the device
[AR1]int g0/0/0 //Enter interface mode
[AR1-GigabitEthernet0/0/0]ip add 10.1.1.2 24
3) Configure router AR2 default name and interface IP
<Huawei>sys
Enter system view, return user view with Ctrl+Z.
[Huawei]sysname AR2
[AR2]int g0/0/0
[AR2-GigabitEthernet0/0/0]ip add 10.1.1.1 24
[AR2-GigabitEthernet0/0/0]int g0/0/1
[AR2-GigabitEthernet0/0/1]ip add 10.1.2.1 24
[AR2-GigabitEthernet0/0/1]int g0/0/2
[AR2-GigabitEthernet0/0/2]ip add 192.168.0.1 24
4) Configure router AR3 default name and interface IP
<Huawei>sys
Enter system view, return user view with Ctrl+Z.
[Huawei]sysname AR3
[AR3]int g0/0/0
[AR3-GigabitEthernet0/0/0]ip add 10.1.2.2 24
5) Configure router AR4 default name and interface IP
<Huawei>sys
Enter system view, return user view with Ctrl+Z.
[Huawei]sysname AR4
[AR4]int g0/0/0
[AR4-GigabitEthernet0/0/0]ip add 192.168.0.2 24
[AR4-GigabitEthernet0/0/0]int g0/0/1
[AR4-GigabitEthernet0/0/1]ip add 172.16.1.1 24
Step 2: Configure IS-IS basic function routing
1) Configure router AR1
[AR1]isis 1
[AR1-isis-1]is-level level-1
[AR1-isis-1]network-entity 10.0000.0000.0001.00
[AR1-isis-1]quit
[AR1]int g0/0/0
[AR1-GigabitEthernet0/0/0]isis enable 1
[AR1-GigabitEthernet0/0/0]q
2) Configure router AR3
[AR3]isis 1
[AR3-isis-1]is-level level-1
[AR3-isis-1]network-entity 10.0000.0000.0002.00
[AR3-isis-1]quit
[AR3]int g0/0/0
[AR3-GigabitEthernet0/0/0]isis enable 1
[AR3-GigabitEthernet0/0/0]quit
3) Configure router AR2
[AR2]isis 1
[AR2-isis-1]network-entity 10.0000.0000.0003.00
[AR2-isis-1]quit
[AR2]int g0/0/0
[AR2-GigabitEthernet0/0/0]isis enable 1
[AR2-GigabitEthernet0/0/0]int g0/0/1
[AR2-GigabitEthernet0/0/1]isis enable 1
[AR2-GigabitEthernet0/0/1]int g0/0/2
[AR2-GigabitEthernet0/0/2]isis enable 1
4) Configure router AR4
[AR4]isis 1
[AR4-isis-1]is-level level-2
[AR4-isis-1]network-entity 20.0000.0000.0004.00
[AR4-isis-1]quit
[AR4]int g0/0/1
[AR4-GigabitEthernet0/0/1]isis enable 1
[AR4-GigabitEthernet0/0/1]int g0/0/0
[AR4-GigabitEthernet0/0/0]isis enable 1
6. Configuration verification:
1. Display IS-IS routing information of each router. There should be a default route in the routing table of the Level-1 router, and the next hop should be the Level-1-2 router. The Level-2 router should have all Level-1 and Level-2 routes, as shown in the figure:
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2. Check the connectivity of each device in the network, as shown in the figure:
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So far, IS-IS basic configuration experiment is completed.
Finally, summarize the differences between OSPF and IS-IS:
1) In IS-IS, each router belongs to only one area; while in OSPF, different interfaces of a router can belong to different areas.
2) In IS-IS, a single area does not have the concept of backbone and non-backbone areas; while in OSPF, Area0 is defined as the backbone area.
3) In IS-IS, both Level-1 and Level-2 routes use the SPF algorithm to generate the shortest path tree SPT (Shortest Path Tree) respectively; while in OSPF, the SPF algorithm is used only in the same area , The routes between areas need to be forwarded through the backbone area