Link ID and adv Router

Link ID and adv Router

Type 1 LSA:
The link state ID is its own RID.
Advertising router is its own RID

It mainly depends on who sent the router LSA.

Type 2 LSA:
Link state ID is the IP address of dr.
Advertising router is the rid of Dr.

Type 3 LSA:
The link state ID is the IP network number.
Advertising router is the ABR's rid

Type 4 LSA:
The link state ID is the rid of adbr.
Advertising router is the ABR's rid

Type 5 LSA:
The link state ID is the IP network number.
Advertising router is the rid of ASBR.

In the p-to-p ospf network type:
The link ID is the neighbor's RID.

In the broadcast OSPF network type:
Link ID is the IP address of dr.

Based on the OSPF network type and network conditions, you can test whether the above information is correct.

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OSPF-LSA type

Different router types are defined. Therefore, multiple types of LSA are required. Generally, type1, type2, type3, type4, type5, and type7.

Type1 is the router LSA. All OSPF speaker will generate this type of LSA and only spread in the region, including the router interface information.

Type2 is a network LSA generated by Dr, including information of all networks connected to Dr, which is only transmitted within the region.

Type3 is a network summary LSA generated by the ABR, which notifies the route entries outside the vro area of the region. When there are multiple ABR entries, use cost to determine, this cost is obtained by adding the external route cost and the internal cost (metric-type 1) by the vro in the region, instead of running the SPF algorithm, therefore, OSPF is a link state protocol in a region, while OSPF is a distance vector protocol between regions.

Type4 is the ASBR summary generated by the ABR and used to broadcast the location of the ASBR. You can see that type4 LSA is always a host mask bandwidth 255.255.255, type5 is the only LSA in the database that does not have the area attribute.

Type5 is the external summary generated by ASBR and is not the routing information of OSPF devices. Generally, in a large network, a large number of such LSA exists in the router database, a heavy load is generated for the vro. So we can use stub area to limit the spread of such LSA.

However, in the following scenarios, if a router running OSPF needs to connect to a non-OSPF network net1 and advertise the route entries in the non-OSPF network to OSPF, instead of storing a large number of external network routes advertised by other routers in the database

In this case, Stub cannot be used, because this will prevent all external routes. The OSPF network will lose the routing information of net1, and type 7 is written into the OSPF standard. To solve this problem, CISCO defines NSSA, type7 transmits external route in NSSA, on NSSA's ABR, type7 is converted to type5 (of course, type7 LSA p-bit = 1), and then the ABR advertises these route entries to backbone. S