Advantages and disadvantages of ospf and application cases

Advantages and disadvantages of ospf and application cases
OSPF is a hierarchical routing protocol. The largest entity in the hierarchy is AS (Autonomous System), which is a part of the Network entity under the management of common routing policies. In each AS, the network is divided into different regions. Each region has its own specific ID number. For the backbone (backbone) area, it is responsible for distributing the link status information between regions. This hierarchical network structure is based on the actual situation of OSPF. When the Autonomous System in the network is very large, the network topology database has more content. Therefore, if there is no hierarchy, on the one hand, it may easily cause database overflow, and on the other hand, when the status of a link in the network changes, it will cause each node in the network to re-calculate its route table, which will not only waste resources and time, but also affect the performance of the routing protocol (such as aggregation speed, stability, flexibility, etc ). Therefore, the autonomous system must be divided into multiple domains. Each domain maintains a unique topology within the domain, and each domain calculates routes based on its own topology, the domain border router summarizes the internal routes of each domain and then spreads between domains. In this way, when the status of a link in the network changes, each vro in the domain where the link is located recalculates the route table of the domain, vrouters in other domains only need to modify the corresponding entries in their route tables, instead of re-computing the entire route table, saving time for route table calculation.
Advantages and disadvantages of Ospf
1) main advantages of OSPF
A. fast Convergence. OSPF is the real LOOP-FREE (no route self-ring) routing protocol. It is derived from its algorithm itself-the link status and shortest path tree algorithm. OSPF is fast in convergence, route changes can be transmitted to the Autonomous System in the shortest time.
B. the concept of regional division is proposed. After autonomous systems are divided into different regions, route information summarization between regions greatly reduces the number of route information to be transmitted, in addition, the routing information does not expand rapidly as the network size expands.
C. Overhead control minimizes the overhead of the Protocol. The objective is as follows:
What is used to discover and maintain the neighbor relationship is a regular hello message without route information, which is very short? Messages that contain route information trigger the update mechanism and are sent only when the route changes. However, to enhance the robustness of the Protocol, all packets are resent every 1800 seconds.
D. In a broadcast network, use multicast addresses instead of broadcasts to send packets to reduce interference with other network devices that do not run OSPF.
E. Is the route trusted? By strictly dividing the route levels (divided into four levels), more trusted routing options are provided.
F. high security and good security. OSPF supports interface-based plaintext and MD5 verification.
G. It has wide adaptability. OSPF is suitable for networks of all sizes and can support up to thousands of servers.
(2) main shortcomings of OSPF protocol
The configuration is relatively complex. Due to the complexity of network area division and network attributes, the network analyst must have a high level of network knowledge to configure and manage the OSPF network.
The routing load balancing capability is weak, although OSPF can be based on the Interface speed? Information such as connection reliability, automatically generate the interface routing priority, but in the routes with different priorities to the same purpose, OSPF only selects the forwarding with higher priority. In the routes with different priorities, cannot I implement load balancing? Only with the same priority can the Server Load balancer be achieved, unlike the way in which the traffic is automatically matched according to the different priority of the VPN gateway.
Ospf region:
1: backbone area (area 0): an autonomous system can only have one backbone area, and each non-backbone area must be connected to the backbone area. The backbone area plays a role in data transfer. The routers in this area are fast, stable, and have fewer routers.
2: standard areas: areas outside the backbone areas are referred to as standard areas. Each standard area must be connected to the backbone areas. If there is no direct connection, you need to configure the virtual link in the region connected to the backbone area, configure the command Router (config-router) # area-id virtual-link router-id
3: Last region: to reduce route entries, only Inter-Domain routes and default routes are accepted in the last region. Configuration command: configure the command Router (config-router) # area-id stub
4: full detail area: in order to reduce route entries, the full detail area only accepts the default route and forwards data through the default route. Configuration command Router (config-router) # area-id stub no-summary
Case
Ospf multi-region configuration and ospf redistribution on R2
A) topology
 
 
B) Some configuration commands and results
R1
Inter f0/0
Ip add 192.168.1.1 255.255.255.0
No shut
Inter s1/0
Ip add 192.168.2.1 255.255.255.0
No shut
Router ospf 10
Network 192.168.1.0 0.0.255 area 1
Network 192.168.2.0 0.0.255 area 1
R2
Inter s1/0
Ip add 192.168.2.2 255.255.255.0
No shut
Inter s1/1
Ip add 192.168.3.1 255.255.255.0
No shut
Inter s1/2
Ip add 192.168.6.1 255.255.255.0
No shut
Router ospf 10
Network 192.168.2.0 0.0.255 area 1
Network 192.168.3.0 0.0.255 area 0
Router VPN 100
Network 192.168.6.0
Router ospf 10
Default-information originate always
Router VPN 100
Redistribute ospf 10 metric 100 100 255 10 1500
R3
Inter s1/1
Ip add 192.168.3.2 255.255.255.0
No shut
Inter s1/0
Ip add 192.168.4.1 255.255.255.0
No shut
Router ospf 10
Network 192.168.3.0 0.0.255 area 0
Network 192.168.4.0 0.0.255 area 2
R4
Inter s1/0
Ip add 192.168.4.2 255.255.255.0
No shut
Inter f0/0
Ip add 192.168.5.1 255.255.255.0
No shut
Inter loop 0
Nos hut
Router ospf 10
Network 192.168.4.0 0.0.255 area 2
Network 192.168.5.0 0.0.255 area 2
R5
Inter s1/2
Ip add 192.168.6.1 255.255.255.0
No shut
Inter s1/0
Ip add 192.168.7.1 255.255.255.0
No shut
Router VPN 100
Network 192.168.6.0
Network 192.168.7.0
R6
Inter s1/0
Ip add 192.168.7.2 255. 255... 255.0
No shut
Inte f0/0
Ip add 192.168.8.1 255.255.255.0
No shut
Inter loop 0
No shut
Router VPN
Network 192.168.7.0
Network 192.168.8.0
Route table information
R1 # show ip rpute
 


R2 # show ip route
 

R3 # show ip route


R4 # show ip route


R5 # show ip route


R6 # show ip route