Open Shortest Path First (OSPF) is an Interior Gateway Protocol (IGP), which is used to make routing decisions in a single autonomous system (AS). It is an implementation of the link state routing protocol and belongs to the IGP, so it operates inside the autonomous system. The famous Dijkstra algorithm is used to calculate the shortest path tree. OSPF supports load balancing and service type based routing, as well as a variety of routing forms, such as host specific routing and subnet routing.
Routing Information Protocol GET THE HERE! is an Interior Gateway Protocol (IGP) and a dynamic routing protocol, which is used for the transmission of routing information in the autonomous system (AS). CISCO protocol is based on Distance Vector Algorithms and uses metric to measure the routing distance to the target address. The router of this protocol only cares about the world around it and only exchanges information with its adjacent routers. The range is limited to 15 hops (15 degrees). CISCO is applied to the application layer of OSI network seven layer model. The administrative distance (AD) defined by each manufacturer is as follows: Huawei defines the preference of routing protocol as 100 and Cisco defines the preference as 120.
Differences between OSPF and CISCO
- Different work cores:
Cisco: count number of hops;
OSPF: calculate link metrics.
2. Whom to send information:
Cisco: only exchange information with adjacent routers;
OSPF: send messages to all routers of the autonomous system. Since the link state information sent by the router can only be transmitted in one direction, OSPF does not have the problem of “slow propagation of bad messages”, and the convergence of the update process is guaranteed.
3. What to send:
Cisco: the information exchanged by the router is all the information currently known by the router, that is, its current routing table;
OSPF: the information sent is the link status of all routers adjacent to this router. It only involves the connection status with adjacent routers, regardless of the scale of the whole Internet.
4. When to send:
Cisco: exchange routing information at fixed time intervals (when the network topology changes, the router also timely notifies the adjacent routers of the routing information after the topology changes);
OSPF: when the network just starts to calculate the first routing table, it must send routing information. Only when the link state changes can the router send this message to all routers by flooding method.
(Link status indicates which routers the router is adjacent to and the measurement of the link)
5.
Cisco: multiple routes cannot be used between two networks at the same time. Select a route with the least routers, that is, the shortest route;
OSPF: if there are multiple paths with the same cost to the same destination network, the traffic can be allocated to these paths to achieve load balance between paths
6
Cisco: limit the network scale. The maximum distance that can be used is 15. 16 means unreachable;
OSPF: the link measurement can be any dimensionless number from 1 to 65535, which can be determined by the manager. Therefore, it is very flexible.
7
Cisco: Version 1 does not support subnet partition, and version 2 supports subnet partition;
OSPF: include subnet mask in routing packet, support variable length subnet division and classless addressing CIDR.
