Table of contents
7. About the irregular area of OSPF
1. Through the tunnel link (Tunnel)
2. OSPF virtual link configuration
3. Multi-process two-way republishing
2. Special area --- used to reduce the number of LSAs in each non-backbone area
7. About the irregular area of OSPF
Divided into two situations:
1. Non-backbone far away from the backbone (border routers between non-backbone areas are illegal devices)
2. Discontinuous backbone
solution:
1. Through the tunnel link (Tunnel)
Establish a tunnel between the backbone area and the illegal ABR, and then announce the tunnel link to the OSPF protocol
shortcoming:
(1) Periodic hello packages and update packages, including trigger updates, will occupy the middle traversal area consistently;
(2) will lead to poor routing
2. OSPF virtual link configuration
The illegal ABR device in the non-backbone area is authorized to forward the route through the legal ABR in the directly connected area. Since there are no new links, there is no problem of poor route selection (one of the problems to be solved)
[r2]ospf 1
[r2-ospf-1]area 1 两台ABR间的直连区域（同时处于该区域）
[r2-ospf-1-area-0.0.0.1]vlink-peer 4.4.4.4 对端ABR的RIDCheck virtual link status
[r2]display ospf vlinkDisadvantage: Periodic resource occupation between two ABRs on the virtual link;
- In Cisco, the periodic update behavior of the two devices is canceled, and the hello package and the update package are sent and received once; --- becomes unreliable
- In Huawei, the retention cycle is updated -- occupying resources
3. Multi-process two-way republishing
ospf multi-process: multiple processes on a router, each process has its own database, calculates routing entries independently, and the calculation results are not shared; finally load all the best paths in the same routing table;
Note: An interface of a router can only work in one process
It can be used to solve irregular areas, separate irregular positions from different processes, and then use republishing technology to share routing tables; solves the problems of poor route selection and resource occupation
[r4]ospf 1
[r4-ospf-1]import-route ospf 2 #将进程2的路由导入到进程1中
[r4-ospf-1]q
[r4]ospf 2
[r4-ospf-2]import-route ospf 1 #将进程1的路由导入到进程2中Eight, OSPF database table
<r1>display ospf lsdb 查看LSDB目录The ospf protocol will use different types of LSAs to transmit topology or routing information under different conditions;
<r1>display ospf lsdb router 2.2.2.2 具体查看某条LSA信息
类别名 link-id（页面）Information Carried by All Types of LSAs
Type : Router category name, here is category 1
Ls id : 2.2.2.2 link-id page number in the table of contents
Adv rtr : 2.2.2.2 Notifier, the RID of the originating device for this LSA
Ls age : 1255 aging time, the normal 1800s period returns to 0, the trigger returns to 0; the maximum aging time is 3609s
Len : 48 Length
Options : ABR E
seq# : 80000016 serial number
chksum : 0x4baa checksum code
| LSA type | Spread range | Announcer | carrying information |
| LSA1 Router | Single region, local region | All routers in a single area | local direct topology |
| LSA2 Network | Single region, local region | DR | Topology of a single MA network segment |
| LSA3 summary | entire OSPF domain | ABR | Inter-Domain Routing Entry |
| LSA4 asbr | The entire ospf domain except the area where the ASBR is located | In the same area as the ASBR (directly connected to the ABR in area 0) | ASBR location |
| LSA5 ase | entire OSPF domain | ASBR | Out-of-Domain Routing Entry |
| LSA7 nssa | single NSSA area | ASBR | Out-of-Domain Routing Entry |
Note: The area where the ASBR is located is based on Type 1 to obtain the ASBR location
| LSA type | link-id | Announcer |
| LSA1 Router | Notifier's RID | All routers in a single area |
| LSA2 Network | IP address of the DR interface | DR in each MA network segment |
| LSA3 summary | Destination network number of inter-domain routing | ABR, when passing through the next ABR, modify |
| LSA4 asbr | RID of ASBR | ABR, when passing through the next ABR, modify |
| LSA5 ase | Destination network number of out-of-domain routing | ASBR |
| LSA7 nssa | Destination network number of out-of-domain routing | ASBR |
Nine, OSPF optimization
Reduce the amount of LSA updates
(1) Summary --- Reduce the number of routing entries in the backbone area
(2) Special area --- reduce the number of routing entries in non-backbone areas
1. Summary
The OSPF protocol does not support interface summarization. In an area, the topology information is passed between adjacencies and cannot be summarized; therefore, it can only be summarized at the border device (ABR) of the interactive route.
(1) Inter-area routing summary: On the inter-area ABR, perform summary configuration when exchanging inter-area routing entries
[r2]ospf 1
[r2-ospf-1]area 1 本地通过该区域1/2类LSA计算所得路由，可以汇总后传递给其他区域
[r2-ospf-1-area-0.0.0.1]abr-summary 3.3.0.0 255.255.252.0(2) Out-of-domain routing summary: ASBR can summarize external routing entries when they share them with the OSPF protocol through the redistribution protocol
[r4]ospf 1
[r4-ospf-1]asbr-summary 99.1.0.0 255.255.252.02. Special area --- used to reduce the number of LSAs in each non-backbone area
Requirements for becoming a special area: cannot be a backbone area, and cannot be configured with virtual links
[1] ASBR cannot exist at the same time
(1) Stub area: Reject Type 4/5 LSAs; the ABR connecting this area to the backbone area issues a Type 3 default LSA to this area
[r2]ospf 1
[r2-ospf-1]area 1
[r2-ospf-1-area-0.0.0.1]stubNote: All routers in this area need to configure this command
(2) Complete stub area: On the basis of the stub area, type 3 LSAs are further rejected; only a type 3 default route is reserved
First configure all routers in the entire area as stub areas; then only configure them on the ABRs connected to the backbone area.
[r2]ospf 1
[r2-ospf-1]area 1
[r2-ospf-1-area-0.0.0.1]stub no-summary[2] Existence of ASBR
(1) NSSA non-complete stub area: This area will reject Type 4/5 LSAs, and the ABR connected to the backbone area in this area will advertise a default route of Type 7 to this area; when the ASBR in this area imports external routes, it will use the Type 7 LSA is imported, and then when the ABR connected to the backbone in this area is passed to the backbone area, it is converted into a type 5 LSA and enters the backbone area;
The focus of NSSA design is not to reduce the extra-domain routes generated by ASBRs in the area, but to reduce the extra-domain routes generated by ASBRs in other parts of the network;
[r2]ospf 1
[r2-ospf-1]area 1
[r2-ospf-1-area-0.0.0.1]nssa 本区域内部所有设备均需配置(2) Complete NSSA: On the basis of NSSA, further deny the entry of Type 3 LSAs, and the ABR connecting the area to the backbone area advertises a Type 3 default route to this area. First configure this area as an NSSA area, and then only The configuration is complete on the ABR connected to the backbone in this area
[r2]ospf 1
[r2-ospf-1]area 1
[r2-ospf-1-area-0.0.0.1]nssa no-summaryRemember: the working environment of NSSA and full NSSA needs to consider the location of the ISP (operator), otherwise it may cause a loop