OSPF Series 5: Link State Updates, Advertisements and Message Formats

LS Updates (and Advertisements):

• Note there is no LS Advertisement packet as such. Link State Update is the type of OSPF packet that carries many LS advertisements

• Each Link State Update packet carries a collection of link state advertisements one hop further from its origin. Several link-state advertisement may be included in a single LS Update packet. If any router notices a change in its networks, it sends that particular type of LS Update to the DR and BDR.

• Link State Update (carries Advertisements), it’s format is as given below:

OSPF Series 4: Configuring OSPF, Wildcard in OSPF, Loopback Interfaces and Router-ID and Transit and Stub Networks

Configuring OSPF:

• Configure IP address on an interface as 1.1.1.1/24
• Then enable OSPF using

OSPF Series 3: DR-BDR Election Process with Flowchart

DR and BDR Selection Process and Flowchart

• The DR and BDR happen for each segment of the network (not for each area). SO, it means one interface of a router can be a DR but another interface of the same router can be a DRO
• The flowchart of selecting the DR and BDR is given below:

OSPF Series 2: OSPF Neighbor States, OSPF Interface States and OSPF Neighborship Formation Requirements

OSPF NEIGHBOR STATES:

• • The below are the neighbour OSPF states:

\1. Down: no OSPF neighbors detected at this moment.

\2. Init: Hello packet received.

\3. Two-way: own router ID found in received hello packet. Then, DR and BDR determined

\4. Exstart: master and slave roles determined.

OSPF Series 1: OSPF Introduction, and Different OSPF Packet Types and Formats

OSPF Introduction:

• OSPF RFC- 2328 https://www.ietf.org/rfc/rfc2328.txt
• To start the OSPF connection, we only need the directly connected connection .ie. only to the neighbour on the same network
• So, on both the routers, we should run #network 10.0.0.1/24 and on the other #network 10.0.0.2/24 .

• 

OSPF PACKET TYPES:

• OSPF Packet Header:

• The OSPF Packet Header is same for all the types of OSPF packets