IS-IS route protocol learning notes

Concept:
 
Chinese name: routing protocol between the intermediate system and the intermediate system
 
IS-IS: Intermediate System to Intermediate System Routing Protocol
 
The routing protocol (IS-IS) between the intermediate system and the intermediate system IS a routing protocol proposed by ISO. It is a link status protocol. In this protocol, the IS (router) IS responsible for exchanging Routing Information Based on Link overhead and determining the network topology. IS-IS similar to the Open Shortest Path First (OSPF) protocol for TCP/IP networks.
 
In the ISO specification, a router IS an IS (intermediate system). The Protocol that provides communication between IS and IS (router and router) IS the routing protocol, that IS, the IS routing protocol. The IS-IS protocol IS similar to the OSPF protocol. It IS both a link-State Routing Protocol. In fact, it appears earlier than the OSPF prototype, OSPF is used in Route Selection for Internet and TCP/IP network IP communication. IS-IS can be used in both IP communication and OSI communication. It can also provide dynamic routing for Information Transmission groups between two routers in the same region.
 
The IS-IS routing protocol IS a link state protocol. It uses the Shortest Path First (Shortest First) algorithm, which has many similarities with the OSPF protocol. The IS-IS routing Protocol belongs to the Internal Gateway Protocol IGP (Interior Gateway Protocol), which IS used inside the autonomous system.
 
IS-IS Concept
 
(1) IS-IS routing protocol terminology
IS (Intermediate System, Intermediate System ). Vro in TCP/IP IS the basic unit for generating routing information and transmitting routing information in IS-IS. In the following section, IS and vro have the same meaning.
 
ES (End System ). It is equivalent to the host system in TCP/IP. ES does not participate in the processing of IS-IS routing protocol, ISO has a dedicated ES-IS protocol to define the communication between the terminal system and the intermediate system.
 
RD (Routing Domain, Routing Domain ). In a routing domain, a group of IS exchange route information through the same routing protocol.
 
Area ). The unit of the route domain.
 
LSDB (Link State DataBase ). All the connection statuses in the network constitute the link status database, and each IS has at least one LSDB. IS uses SPF algorithm and LSDB to generate its own route.
 
LSPDU (Link State Protocol Data Unit ). In IS-IS, each IS generates an LSP, which contains all the link status information of this IS. Each IS collects all LSPs in the region to generate their own LSDB.
 
Network Protocol Data Unit (NPDU ). It is a network-Layer Protocol packet in ISO, which is equivalent to an IP packet in TCP/IP. DIS (Designated IS) IS the specified intermediate system on the broadcast network.
Network Service Access Point (NSAP ). Is the network layer address in ISO. Identifies an abstract network-layer access service point and describes the network address structure of the ISO model.
 
(2) link types applicable to IS-IS Routing Protocol
IS-IS can run on Point-to-Point Links, such as PPP and HDLC, or Broadcast Links, such as Ethernet and Token-Ring, for NBMA (Non-Broadcast Multi-Access) networks, such as ATM, You need to configure the sub-interface for it and set the sub-interface type to P2P or Broadcast network. IS-IS cannot run on a Point to Multi Point Links.
 
3. IS-IS routing protocol structure
 
To support large-scale routing networks, IS-IS uses two layers in the routing domain. A large routing domain is divided into one or more regions. Routes in a region are managed by Level-1 routers, and routes between regions are managed by Level-2 routers.
 
(1) Level-1 Router
The Level-1 router is responsible for the routing in the region. It forms a neighbor relationship with the Level-1 router or Level-1-2 router in the same region and maintains a Level-1 LSDB, the LSDB contains the routing information of the region and forwards the packets outside the region to the nearest Level-2 router.
 
(2) Level-2 Router
Level-2 routers are responsible for routing between regions. They can form a neighbor relationship with Level-2 routers or Level-1-2 routers in other regions to maintain a Level-2 LSDB, this LSDB contains routing information between regions. All Level-2 routers constitute the backbone network of the routing domain and are responsible for communication between different regions. The Level-2 router in the routing domain must be continuous to ensure the continuity of the backbone network.
 
(3) Level-1-2 Router
A vro that belongs to both Level-1 and Level-2 is called a Level-1-2 router. Each region has at least one Level-1-2 router to connect the region to the backbone network. It maintains two LSDB. LSDB of Level-1 is used for intra-region routing, and LSDB of Level-2 is used for inter-region routing.
 
4. IS-IS packets used by the Routing Protocol
 
IS-IS packets are directly encapsulated in Data Link frames, which are classified into three types: Hello packets. LSP and SNP.
 
(1) Hello Message
A Hello message IS used to establish and maintain a neighbor relationship, also known as IIH (IS-to-IS Hello PDUs,
The Level-1 router in the broadcast LAN uses Level-1 lan iih; The Level-2 router in the broadcast LAN uses Level-2 lan iih; and the Level-to-Point IIH router in non-broadcast networks.
 
(2) LSP
LSP (Link State Packet ). Used to exchange link status information. There are two types of LSP: Level-1 LSP and Level-2 LSP. Level-2 LSP is transmitted by Level-2 router, Level-1 LSP is transmitted by Level-1 router, and Level-1-2 router can transmit the above two types of LSP.
 
(3) SNP
SNP (Sequence Number Packet, time series Packet ). The LSP is used to confirm the newest received between neighbors. It is used for similar Acknowledge packets, but is more effective. SNP includes CSNP (Complete SNP, full-time packet) and PSNP (Partial SNP, some time series packets ), it is further divided into Level-1 CSNP, Level-2 CSNP, Level-1 PSNP, and Level-2 PSNP.
 
PSNP only lists the numbers of one or more recently received LSPs. It can confirm multiple LSPs at a time, PSNP is also used to request the neighbor to send a new LSP.
 
CSNP includes summary information of all LSP in LSDB, so that LSDB can be synchronized between adjacent routers. On a broadcast network, CSNP is sent regularly by DIS (the default sending cycle is 10 seconds). On a point-to-point line, CSNP is sent only when the connection is established for the first time.
 
IS (Intermediate System, Intermediate System ). Vro in TCP/IP IS the basic unit for generating routing information and transmitting routing information in IS-IS. In the following section, IS and vro have the same meaning.
 
ES (End System ). It is equivalent to the host system in TCP/IP. ES does not participate in the processing of IS-IS routing protocol, ISO has a dedicated ES-IS protocol to define the communication between the terminal system and the intermediate system.
 
RD (Routing Domain, Routing Domain ). In a routing domain, a group of IS exchange route information through the same routing protocol.
 
Area ). The unit of the route domain.
 
LSDB (Link State DataBase ). All the connection statuses in the network constitute the link status database, and each IS has at least one LSDB. IS uses SPF algorithm and LSDB to generate its own route.
 
LSPDU (Link State Protocol Data Unit ). In IS-IS, each IS generates an LSP, which contains all the link status information of this IS. Each IS collects all LSPs in the region to generate their own LSDB.
 
Network Protocol Data Unit (NPDU ). It is a network-Layer Protocol packet in ISO, which is equivalent to an IP packet in TCP/IP. DIS (Designated IS) IS the specified intermediate system on the broadcast network.
 
Network Service Access Point (NSAP ). Is the network layer address in ISO. Identifies an abstract network-layer access service point and describes the network address structure of the ISO model.
 
IS-IS comparison with OSPF
 
1) IS-IS only defines two network topology types: broadcast and general topology. In a Cisco router, links are divided into point-to-point and broadcast.
OPSF defines five network types: point-to-point, point-to-multipoint, broadcast and NBMA, and virtual links
2) both Protocols maintain a Link State Database)
IS-IS uses LSP (Link State PDU), and LSP itself IS a datagram;
When OSPF uses LSA (Link State Advertisements), LSA must be encapsulated in the OSPF header and IP header.
 
3) both Protocols use the SPF algorithm to calculate routes.
IS-IS runs Level 1 SPF computing route in the domain (intra-area), and runs Level 2 SPF computing route between domains (inter-area;
OSPF runs SPF computing routing in the domain (intra-area), and runs the distance vector (distance vector algorithm) algorithm between domains (inter-area) to calculate the routing.
 
4) both Protocols use the domain (area) to establish a two-layer hierarchical network topology.
The IS-IS backbone IS composed of a continuous Level 2 router instead of a specific domain;
The OSPF backbone must have and must be area 0;
IS-IS domain boundaries are on links between routers;
The domain boundary of OSPF is on the router;
The two-layer hierarchical network topology of IS-IS not required. The network can be completely composed of a Level 1 router or a Level 2 router.
OSPF must have area 0, which can have only one area, but must be area 0.
 
5) one of the features of IS-IS: the IS-IS router can have a maximum of three domain addresses (area addresses), which IS useful in Inter-Domain transmission.
 
6) The two protocols are non-class routing protocols, both of which are summarized between areas (summary)
 
7) The two protocol handling errors (upted) LSP/LSA methods are different:
IS-IS any vro can discard (purge) corrupted LSP;
In OSPF, only the sender (originator) of the upted LSA can discard (purge) it.
 
8. The adjacency relationship must be established between the two protocols in the broadcast network.
IS-IS, as long as your identity IS in the neighbor Hello datagram, the adjacency relationship IS established successfully. This stage goes through a three-way handshake process: Down → Init → Up.
The process before the adjacency relationship is established in OSPF: Down → Init → Two-way → Exstart → Exchange → Uploading → Full.
 
9) IS-IS neighbors will establish an adjacency relationship, even if Hello-intervals or Hello multipliers are different;
OSPF neighbors does not establish an adjacency relationship, if Hello-intervals or Dead-intervals is different.
 
10) in the broadcast network, You must select a DIS/DR protocol for both Protocols.
In IS-IS, dis is dynamically selected. That IS, if a vro with a higher priority or greater address IS added to the network, the newly added vro becomes DIS;
DR is relatively stable in OSPF, that is, as long as the DR has not been down, the DR maintains its position;
In IS-IS, the router in the broadcast network establishes an adjacency relationship with all its neighbors;
In OSPF, the router in the broadcast network only establishes an adjacency relationship with the DR and BDR neighbors;
In IS-IS, dis is not synchronized with its neighbors (synchronize ). DIS generates the pseudo-donode for the LAN and sends PSNPs (partial sequence number PDUs) every 3 seconds or sends csnp (complete sequence number PDUs) every 10 seconds ). Other routers can also use PSNPs to request a lost LSP from DIS or send a new LSP to DIS. Because DIS can flood PDUs, DIS does not need to be synchronized with its neighbors (synchronization); because it does not need to be synchronized with its neighbors (synchronization), BDIS is not required.
In OSPF, DR/BDR uses the unicast (unicast) transmission mode to synchronize with other routers (synchronization ).
 
11) both protocols have authentication)
IS-IS only supports Simple authentication;
OSPF supports Simple authentication and MD5 authentication.
 
12) the IS-IS L1/L2 Router does not publish L2 routes to the L1 router. A L1 router is like a full-end domain (totally stubby area) in OSPF ).
 
13) There is no configuration option in the configuration of the ISIS protocol similar to the ip OSPF network command in the ospf protocol, therefore, the ROUTER in NBMA as the "HUB" must be configured as point to point subinterfaces (including address changes) so that each PVC link is in a different SUBNET.