Below is my scenario with 2 Routers and each router configured with 3 loopback interface and two Fast Ethernet interfaces are up.
(Router A - loopback networks: 10.1.1.1/8, 11.1.1.1/8, 12.1.1.1/8 and Fast Ethernet 0/1 99.99.99.1/24 and Fast Ethernet 0/0 100.100.100.1/24).
(100.100.100.1) (100.100.100.2)
Router A Router B
----------Down staste----------
----------init staste----------
----------two-way staste-------
----------extart staste--------
After master Slave negotiation, Router A considered as Slave and send below DBD packet with a summary of the LSDB which contain LSA-type 1 (Router-LSA)
Ethernet II, Src: c4:01:0a:84:00:00 (c4:01:0a:84:00:00), Dst: c4:02:03:f4:00:00 (c4:02:03:f4:00:00)
Internet Protocol Version 4, Src: 100.100.100.1, Dst: 100.100.100.2
Open Shortest Path First
OSPF Header
OSPF DB Description
Interface MTU: 1500
Options: 0x52 (O, (L) LLS Data block, (E) External Routing)
DB Description: 0x02 ((M) More)
.... 0... = (R) OOBResync: Not set
.... .0.. = (I) Init: Not set
.... ..1. = (M) More: Set
.... ...0 = (MS) Master: No
DD Sequence: 242
LSA-type 1 (Router-LSA), len 72
.000 0000 0011 0101 = LS Age (seconds): 53
0... .... .... .... = Do Not Age Flag: 0
Options: 0x22 ((DC) Demand Circuits, (E) External Routing)
LS Type: Router-LSA (1)
Link State ID: 12.1.1.1
Advertising Router: 12.1.1.1
Sequence Number: 0x80000001
Checksum: 0x2157
Length: 72
OSPF LLS Data Block
In your explanation,
“In the exchange state, our routers are sending a DBD with a summary of the LSDB. This way the routers can find out what networks they don’t know about”.
My question:
- When Router B receives this DBD packet from Router A, how Router B understand that Router A connected networks ( 10.1.1.1/8, 11.1.1.1/8, 12.1.1.1/8,99.99.99.1/24,100.100.100.1/24) ? this network information is not shown in the LSA-type 1 (Router-LSA).Now How Router B will find out that what networks they don’t know about and what networks they know about?
2)Router A is sending Sequence Number: 0x80000001 and now what Sequence Number Router B will have to compare with Sequence Number received from Router A ?