What are the different OSPF packet types? (5)
- Type 1: 0x01 - Hello Packets
- Type 2: 0x02 - Database Description (DD) Packets
- Type 3: 0x03 - Link State Request (LSR) Packets
- Type 4: 0x04 - Link State Update (LSU) Packets
- Type 5: 0x05 - Link State Acknowledgement (LSA)
What is Type 1: 0x01 - Hello Packet used for?
used as a first packet to be sent for establishing and maintaining adjacencies with neighboring OSPF devices
What is the role of the Type 1: 0x01 - Hello Packet?
- ensure two-way communication exists
- contain attributes that neighbors must agree on to form adjacency
- serve as a failure detection mechanism
What is the TTL value of Type 1: 0x01 - Hello Packet?
TTL value of Hello packet is set to 1
What do Type 1: 0x01 - Hello Packets communicate? (9)
- network/subnet mask
- Hello interval
- options
- router priority
- router Dead Interval
- DR/BDR
- neighbor
What do the Type 2: 0x02 - Database Description (DD) Packets carry and contain?
carry LSA headers and contain abbreviated link-state database
What are the Type 2: 0x02 - Database Description (DD) Packets used for?
for synchronization of link-state databases between OSPF devices
What do Type 2: 0x02 - Database Description (DD) Packets communicate?
- link’s MTU
- LSA Headers
- DBD Sequence Number
- DBD bits
- options
Do LSA headers contain the entire LSA?
no, they contain just enough information for device that exchange these packets whether they need to send an LSR
What are the Type 3: 0x03 - Link State Request (LSR) Packets used for?
to request missing information for LSAs seen during the DBD packet exchange; could be a reaction to a sender of DD packet
What do the Type 3: 0x03 - Link State Request (LSR) Packets communicate?
- type of LSA being requested
- link-state ID of the LSA
- Router ID of the router responsible for originating the LSA
What are the Type 4: 0x04 - Link State Update (LSU) Packets used for?
- distribute information about the state of OSPF routers within an OSPF area
- convey information about the state of OSPF routers, including their Router IDs and the state of their interfaces
What do the Type 4: 0x04 - Link State Update (LSU) Packets contain? (4)
- Router ID
- Link-State Advertisement (LSA) Header
- Link-State ID
- Advertising Router
What is the role of the Type 4 LSU packets when a router changes its state or when there are changes in the network topology, such as an OSPF router going up or down?
Type 4 LSU packets are used to update all OSPF routers in the area about these changes, therefore they play a crucial role in the synchronization process
What are the Type 5: 0x05 - Link State Acknowledgement (LSAck) used for?
- confirmation that LSU transfer has been successful
- sent as multicast for broadcast networks
What do the Type 5: 0x05 - Link State Acknowledgement (LSA) communicate?
only the LSA header information of the LSAs which are being ACKd
What is the L3 destination IP address used by OSPF Hello Packets?
L3 224.0.0.5 multicast address on broadcast networks
What is the address type of OSPF Hello Packets on a non-broadcast network?
unicast
What is the L2 destination IP address used by OSPF Hello Packets?
either 01-00-5E-00-00-05 | 01-00-5E-00-00-06 multicast address
What are the 3 basic functions provided by OSPF Hello packets?
- ensure two-way communication exists
- exchange attributes that neighbors must agree on to form adjacency
- serve as a failure detection mechanism
