ospf protocol rip

“What are the similarities and differences between the RIP protocol and the OSPF protocol?

Similarities: both are IGP routing protocols that support dynamic route learning, RIPV2 and OSPF support VLSM, both are multicast updates and support authentication.

Differences: RIPV2OSPF

Distance vector routing protocols link-state routing protocols

Automatic summarization is enabled by default, summarized routes are based on interfaces are not summarized by default, summarized routes are based on areas

Support for interface explicit or MD5 authentication support for areas and interfaces explicit or MD5 authentication

Periodic updating, updating If not in time, there will be a loop to trigger the update, no loop

Overhead in terms of the number of hops, does not recognize the bandwidth to run the SPF algorithm to calculate the overhead, to recognize the bandwidth

Periodic update of the entire routing table in the region to exchange LSAs to build the LSDB, and then derive the routing table

Briefly describe the principles of static routing, RIP and OSPF dynamic routing and the advantages and disadvantages of each.

Principle of static routing: the routingentry is manually configured, not dynamically determined. Unlike dynamic routes, static routes are fixed and do not change, even if the network conditions have changed or been reconfigured. Typically, static routes are added to the routing table on an item-by-item basis by a network administrator.

Benefit: Another benefit of using static routing is the high level of network security and confidentiality. Dynamic routing because it requires routers to frequently exchange their routing tables with each other, and the analysis of the routing tables can reveal information such as the topology of the network and network addresses. Therefore, networks can also use static routing for security reasons. Does not consume network bandwidth because static routes do not generate update traffic.

Disadvantage: Static routing is usually not appropriate for large and complex network environments. On the one hand, it is difficult for network administrators to have a comprehensive understanding of the topology of the entire network; on the other hand, when the topology and link state of the network changes, the static routing information in the router needs to be adjusted on a large scale, which is a very difficult and complex task. When the network changes or the network fails, the routes cannot be rerouted and are likely to make the routes fail.

RIP Principles:

1. Initialization.When RIP is initialized, a request packet is sent from each interface involved in the job. This request packet requests a complete routing table from all RIP routers. The request is accomplished by sending the LAN in the form of a broadcast on the LAN or on a point-to-point link to the next hop address. This is a special request for a complete routing update from neighboring devices.

2. receive requests. there are two types of messages in RIP, response and receive messages. Each route entry in the request packet is processed to create a metric for the route as well as a path.RIP uses a hop count metric, where a value of 1 means that there is a directly connected network and 16, that the network is unreachable. The router returns the entire routing table as an answer to the incoming message.

3. The response is received. The router receives and processes the response, which it updates by adding, deleting, or modifying routing table entries.

4. Routine routing updates and timing. The router sends the entire routing table to neighboring routers in the form of an answer message once every 30 seconds. When the router receives an update for a new route or an existing route, it sets a timeout of 180 seconds. If there is no update for 180 seconds, the route’s hop count is set to 16, and the router announces the route with a metric of 16 until the refresh timer removes the route from the routing table.

The refresh timer is set to 240 seconds or 60 seconds more than the expiration timer time. and Cisco uses a third timer called the suppression timer. The 180 seconds after receiving a route with a higher metric is the suppression timer time, during which time the router does not update the routing table with the new information it receives, which can provide an additional period of time for the net to converge.

5. Trigger routing updates. When a routing metric changes, the router sends only the routes associated with the change, not the complete routing table.


Information is exchanged only with neighboring routers. Two routers are neighboring if communication between them does not go through another router.The RIP protocol states that no information is exchanged between routers that are not neighboring.

The information exchanged by a router is all the information currently known to this router. That is, its own routing table.

Routing information is exchanged at fixed intervals, e.g., every 30 seconds, and then routers update their routing tables based on the routing information they receive.


1. Overly simple, calculating metrics based on the number of hops often results in non-optimal routes.

2, the metric value is limited to 16, not suitable for large networks.

3. Poor security, accepts route updates from any device. No password authentication mechanism, accepts routing updates from any device anywhere by default. Cannot prevent malicious rip spoofing.

4. Classless ip address and VLSM<ripv1> are not supported.

5. Poor convergence, often greater than 5 minutes.

6, consumes a lot of bandwidth. Complete replication of the routing table, copying its own routing table to all neighbors, especially on low-speed WAN links more explicitly updated in full.

OSPF principle:

1, the initialization of the formation of the initial port information: in the initialization of the router or network structure changes (such as changes in the link, the router is new or damaged), the relevant router will produce a link state broadcast packet LSA, which contains all the links connected to the router, that is, all the ports of the state of information.

2. Routers exchange link status information through the flooding mechanism: each router transmits its LSA packet to all of its neighboring OSPF routers on the one hand, and receives LSA packets from its neighboring OSPF routers on the other hand, and updates its own database accordingly.

3. Formation of a stable area topology database: OSPF routing protocols converge gradually through the flooding method to form a database of the area’s topology, at which point all routers retain a copy of the database.

4. Formation of routing tables: All routers form their own routing tables based on their copies of the area topology database using the shortest path method.

Advantages: OSPF is suitable for networks in large areas; multicast-triggered updates; fast convergence; overhead as a metric; OSPF protocol is designed to avoid routing loops; widely used.

Disadvantages: The OSPF protocol configuration requires a high level of skill and is more complex to configure; routing its own load-sharing capacity is very low.