1. Irregular areas of OSPF
1) Non-backbone areas far away from the backbone
2) Discontinuous backbone areas—After the routes from area x are learned locally, they cannot be shared to area X.
Solutions:
1. Ordinary GRE, tunnel tunnel
Use tunnel to establish a new logical link between legal and illegal ABR; then announce the link to the OSPF protocol
Disadvantages:
1) Periodic OSPF needs to be actually transmitted through the intermediate area, which greatly increases the resource occupation of the intermediate area
2 ) Poor routing—When the ospf device receives two routes to the same network segment, it first pays attention to the area IDs obtained by the two routes; backbone areas are better than non-backbone areas
2. Multi-process two-way re-release-the best solution
Re-release: use ASBR (autonomous system border router, protocol border router) between
multiple protocols. Multi-process: If multiple OSPF processes are started at the same time on a device, different processes will be announced Different interfaces have their own databases and are not shared; only the calculated routes are loaded into the same routing table;
At the illegal ABR, the interfaces of different areas are announced to different processes to form an independent database; after that, the re-release technology is used to realize route sharing, and the whole network is reachable; there is no worry about routing problems and resource occupation problems;
[r4]ospf 1
[r4-ospf-1]import-route ospf 2
[r4-ospf-1]q
[r4]ospf 2
[r4-ospf-2]import-route ospf 1
3. The virtual link technology of OSPF The
legal ABR authorizes the illegal ABR, and then the illegal ABR can share routes between areas.
[r2]ospf 1
[r2-ospf-1]area 1 Enter the traversal area
[r2-ospf-1] -area-0.0.0.1]vlink-peer 4.4.4.4 RID of the peer ABR;
Advantages: No new channels are established, and there is no problem of poor routing;
Disadvantages: 1. Periodic information between two ABR devices still affects the intermediate image—Huawei
2. No keep-alive between two ABR devices, no cycle Information; it can be unreliable—cisco
2. OSPF database table
[r1]display ospf lsdb View database directory
[r1]display ospf lsdb router 1.1.1.1 View the entry information in detail
Category name link-id (page number)
OSPF Process 1 with Router ID 1.1.1.1
Area: 0.0.0.0
Link State Database The
following information is for all entries.
Type: Router category name
Ls id: 1.1.1.1 link-id (page number)
Adv rtr: 1.1.1.1 RID of the notifier, source
Ls age: 723 aging time, 1 second plus 1; 1800s cycle return to 0, trigger current return to 0, maximum aging 3609
Len: 48 Length
Options: E Marking bit
seq#: 80000016 Serial number
chksum: 0x6d96 Check box code
The OSPF protocol uses different types of LSAs to transmit routing or topology information in different environments;
1:Router The LSA generated by each router in the
OSPF routing domain is the basis of the LSA advertisement , which is listed in the LSA packet,
The IP address and mask of all ports participating in the OSPF process of this router and the metric value of the interface. The LSA will only be diffused in the area where the sending router is located , that is, its scope of action is this area
2: Network
type LSA in the network topology is produced only in the case of multiple access, the LSA package such, this list of multiple access mask using Router-id way to describe this physical segment within How many routers keep in touch with DR
3: Network-summary
Type 3 LSA is issued by BDR. The main reason for the existence of this type of LSA is that Type 1 and Type 2 can only be transmitted within the domain and cannot cross regions . In this type of data packet, the network segment, mask, The metric value of the outbound interface reaching the target network segment, so Type 3 LSA is equivalent to packing Type 1 and Type 2 LSAs and transmitting them to other areas through ABR
Type 4: ASBR-summary
This type of LSA has no special meaning. The Router-id method is used in the data packet to locate the ABR in the area where the ASBR and ASBR are located , so that other routers can find the location of the ABR
Type 5: external the
entire OSPF domain , the notifier is ASBR , and the route outside the domain (re-advertises the incoming route)
Type 7: NSSA LSA (Type 7)
is generated by ASBR, describes the route to the outside of the AS , and only spreads in the NSSA area .