OSPF

Question 1

LSA

Answer 1

Link State Advertisement:
Routers exchange these to maintain consistent databases

Network changes generate them
LSDBs are composed of all received LSAs

Question 2

A link state update contains:

Answer 2

An OSPF header and a string of LSAs

Each LSA has its own header
Routers acknowledge the receipt of LSAs

Question 3

Forming an OSPF Adjacency

Answer 3

Down: initial state
Init: Hello packets was seen from a non-adjacent neighbor
2-way: Communication is bidirectional between the two routers
ExStart: A primary and secondary relationship is negotiated
Exchange: Database description packets are exchanged
Loading: LSA information is exchanged
Full: LSDBs are identical

Question 4

Adjacency Requirements

Answer 4

Primary IP address of peers are in the same subnet with the same mask
Interfaces of peers are the same type and in the same OSPF area
Hello and dead intervals of peers must match
Each peer has a unique router ID
OSPF IP maximum transmission units (MTUs) match
OSPF authentication, if enabled, is successful

Question 5

OSPF status command

Answer 5

get router info ospf status

Question 6

OSPF interface command

Answer 6

get router info ospf interface

States-
DR: Designated Router
BDR: Backup Designated Router
DROther: Neither DR nor BDR

shows info of DR and BDR

also shows number of neighbor and adjacencies

Question 7

OSPF Neighbors command

Answer 7

get router info ospf neighbor

State column-
Displays the adjacency state and whether the interface is a DR, BDR, or neither (DROther)
Dash(-) represents point-to-point network

Question 8

OSPF LSDB command

Answer 8

get router info ospf database brief

shows the LSDB entries ordered by LSA Types

Question 9

LSA Type 1

Answer 9

get router info ospf database router lsa

AKA router link states

Question 10

Self-Originated LSAs

Answer 10

LSAs that originated on the local FGT

get router info ospf database self-originate

Question 11

OSPF Protocol/Port

Answer 11

IP/89

Question 12

OSPF Real-Time Debug

Answer 12

diagnose ip router ospf all enable
diagnose ip router ospf level info
diagnose debug enale

to Disable:
diagnose ip router ospf all disable
diagnose ip router ospf level none
diagnose debug disable

Diagnose debug reset does NOT stop it

Question 13

Command to restart OSPF process

Answer 13

execute router clear ospf process

by default, routing real-time debugs stop running after restarting the routing process

can use the ‘zl’ flag to make it persist after restart
diagnose ip router zl enable

Question 14

Type 5 LSAs

Answer 14

AS External Link States

Question 15

OSPF Logging

Answer 15

FGT logs:
Neighbor down/up
OSPF message exchange
Negotiation errors

enabled by default:
config router ospf
set log-neighbor-change enable
end

Can also be seen in GUI under: Log & Report > System Events > Router Events