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OSPF network planning

OSPF network planning can be considered from the following aspects:

1. The design steps of OSPF network are divided into the following steps:

1) demand analysis: the customer's perspective is very important, in addition to consider the future development direction and so on. The reliability, delay, traffic, multi-protocol and the difficulty of configuration are considered in the network design. When designing an OSPF network, the load balancing of the network and the convergence of routing need to be considered.

2) establish the network topology: adopt the hierarchical structure, the core layer provides interconnection for the backbone area and other areas, and the access layer is the company department such as each business department, or the server area.

3) IP address planning: mainly considering route summary and marking special equipment with characteristic IP address

4) prepare hardware: select devices according to network requirements, such as CPU, RAM, forwarding time, etc.

5) upgrade IOS: upgrade device IOS according to network needs and device stability

6) configure and implement the network: configure devices to achieve monitoring

2. In terms of OSPF area size, you need to consider LSDB size, LSA flooding and other aspects. The general scale is recommended as shown in Table 11.1.

Table 11.1 OSPF area planning parameters table

Parameters.

Minimum value

Average value

Maximum value

Number of routers per domain (autonomous system)

one

five hundred

one thousand

Number of routers per area

one

one hundred

three hundred and fifty

Number of regions in each domain (autonomous system)

one

twenty-five

seventy-five

Number of neighbors per router

one

fifty

one hundred

Number of areas per router

one

three

five

3. Select designated routers. Since DR and BDR have the most OSPF work, all routers with good performance and low CPU utilization should be selected as DR and BDR. For example, if a router is configured with a lot of antivirus ACL and its traffic is high, the router CPU utilization is generally high. If this router becomes a DR, it may cause high CPU utilization and affect route synchronization and convergence.

4. The memory, CPU and bandwidth of the router all need to be considered in large networks to avoid failure.

5. The design of OSPF area includes the following points:

1) consider physical proximity: divide physically adjacent devices into an area

2) Link instability has a reduced area size, which can avoid route recalculation caused by link packet loss.

3) make sure that the regions are continuous, and all areas must be continuous, otherwise they need to cooperate with virtual links

4) all areas should be connected to the backbone area

5) if possible, two ABR can be set up in the backbone area and the standard area to achieve redundancy.

6) summarize routes as much as possible

7) the backbone area should be stable, be continuously monitored, achieve redundancy in the design as far as possible, keep it simple, the fewer routers, the better, and keep the bandwidth symmetrical to achieve load balancing.

8) Virtual links and ASBR are not allowed in the stub area. If you design an ASBR, you need to set this area to the NSSA area, and the backbone area cannot be set to the stub area.

6. According to the usual work, there are several important points in the above design specifications, and the common ones are:

1) according to the requirements of the OSPF agreement, the non-backbone area needs to be connected to the backbone area, and all branches need to be connected to the head office, so the head office is configured as the backbone area (core layer), and each branch is a non-backbone area (access layer).

2) due to different geographical conditions, some branches are close to each other but far away from the head office, so one branch can be connected to another branch and then connected to the head office, and virtual links can be used in OSPF configuration (virtual links can be flexibly used in the work of virtual links, but do not appear as far as possible in OSPF networks)

3) for smaller branches or sales outlets, static routes can be configured instead of OSPF

4) the edge area can be configured as a stub area to reduce routing entries

5) summarize the routes as much as possible, reduce the routing table, and avoid the phenomenon of high CPU utilization or insufficient memory caused by too many routing entries on the router.

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