directory title
About the Irregular Area Problem of OSPF
- non-backbone away from backbone
- discontinuous backbone
Solve the problem
1. Tunnel establishes a tunnel between the backbone area and the illegal ABR, and then announces the tunnel link to the OSPF protocol;
Disadvantages:
1) Periodic hello and update, including trigger update, will always occupy the intermediate traversal area;
2) Poor routing
2. OSPF virtual link
The illegal ARB device is authorized by the legal ABR in the directly connected area to forward the route;
since there is no new link, there is no problem of poor route selection;
[r2]ospf 1
[r2-ospf-1]area 1 两台ABR间的直连区域（同时处于该区有）
[r2-ospf-1-area-0.0.0.1]vlink-peer 4.4.4.4 对端ABR的RID
[r2]display ospf vlink 查看虚链路
Disadvantages : Periodic resource occupation between two ABRs on the virtual link;
1) In Cisco, the periodic behavior of the two devices is canceled, hello and update are sent and received once; ---- unreliable
2) In Huawei, Retain cycle; — accounts for resources
3. Multi-threaded two-way republishing
ospf multi-process: multiple processes on a router, each process has its own database, and independently calculates routing entries, and the calculated results of 1 are not shared; finally, the best path obtained is loaded into the same routing table; the router
's An interface can only be in one process;
it can be used to solve irregular areas, separate the process of working in irregular positions, and then use republishing technology to share the routing table;
solve the problem of poor route selection and resource occupation
[r4]ospf 1
[r4-ospf-1]import-router ospf 2 把进程2的路由共享到进程1
[r4-ospf-1]q
[r4]ospf 2
[r4-ospf-2]import-router ospf 1 把进程1的路由共享到进程2
OSPF database tables
<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
Information carried by all types of LSAs:
| carry information | analyze |
|---|---|
| Type：Router | Category name, here is category 1 |
| Ls id：2.2.2.2 | link-id, the page number in the table of contents |
| Adv rtr：1255 | Aging time, the normal 1800s period returns to 0, the trigger returns to 0; the maximum aging is 3609s |
| Len：48 | length |
| Options：ABRE | |
| seq#：80000016 | serial number |
| chksum：0x4baa | checksum code |
LSA type
| LSA type | Spread range | Announcer | carrying information |
|---|---|---|---|
| LSA1 Router | Single region, local region | All routes within a single area | local direct topology |
| LSA2 Network | Single region, local region | DR | Topology of a single MA network segment |
| LSA3 summary | The entire ospf area | ABR | Inter-Domain Routing Entry |
| LSA4 asbr | The entire ospf domain except the area where the ASBR is located | An ABR that is in the same area as the ASBR and is directly connected to area 0; the ASBR location is obtained based on type 1 in the area where the ASBR is located | ASBR location |
| LSA5 ase | The entire ospf domain | ASBR | Out-of-Domain Routing Entry |
| LSA7 nssa | single NSSA area | ASBR | Out-of-domain routing |
| LSA type | link-id | Announcer |
|---|---|---|
| LAS1 Router | Notifier's RID | All routers in a single area |
| LSA2 Network | IP address of the DR interface | DR in each 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 |
OSPF optimization – reduce the amount of LSA updates
- Summarize – reduce the number of routing entries in the backbone area
- Special Areas – Reduce the number of routing entries for non-backbone areas
summary
The OSPF protocol does not support interface summarization. It is always within an area, and the topology information is transmitted between adjacencies, which cannot be summarized; therefore, it can only be summarized on the cousin device of the interactive route;
Inter-domain route summary
On the inter-area ABR, perform summary configuration when exchanging inter-area routing entries
[r2]ospf 1
[r2-ospf-1]area 1 本地经过该区域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 3.3.0.0 255.255.255.0
Out-of-domain route summary
When ASBR shares the external routing entries into the OSPF protocol through the redistribution protocol, it can summarize;
[r4]ospf 1
[r4-ospf-1]asbr-summary 99.1.0.0 255.255.252.0
special area
The number of LSAs used to reduce each non-backbone area
cannot be a backbone area, and virtual links cannot be configured
ASBR cannot exist at the same time
Peripheral area
Reject Type 4/5 LSAs; the ABR connected to the backbone area sends a Type 3 default LSA to this area
[r2]ospf 1
[r2-ospf-1]area 1
[r2-ospf-1-area-0.0.0.1]stub
注：该区域的所有路由器均需配置该命令
completely peripheral area
On the basis of the stub area, further reject type 3 LSA; keep only one type 3 default route; first
configure all the routers in the entire area as stub areas; and then only complete the configuration on the ABR connected to the backbone area;
[r2]ospf 1
[r2-ospf-1]area 1
[r2-ospf-1-area-0.0.0.1]stub no-summary
ASBR exists
NSSA non-peripheral area
This area will reject Type 4/5 LSAs, and the ABR connected to the backbone area in this area will advertise a Type 7 default route to this area; when the ASBR in this area imports external routes, it will import based on Type 7, and then connect to the backbone through this area When the ABR in the ABR transmits the backbone area, it is converted into category 5 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 本区域内所有设备均需要配置
Full NSSA
On the basis of NSSA, further deny the entry of Type 3 LSAs, and the ABR that has this area connected to the backbone area issues a Type 3 default to this area. First
configure this area as an NSSA area, and then only connect to the backbone ABR in this area. The above configuration is complete;
[r2]ospf 1
[r2-ospf-1]area 1
[r2-ospf-1-area-0.0.0.1]nssa no-summary
Remember: the working environment of NSSA and full NSSA needs to consider the location of the ISP (operator), otherwise it may cause a loop