Differences between ISIS and OSPF

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
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.

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