OPEN SHORTEST PATH FIRST (OSPF) QUICK REFERENCE TABLE:

---

OPEN SHORTEST PATH FIRST (OSPF) QUICK REFERENCE TABLE :

---

Open Shortest Path First (OSPF) Is A Link State Based Interior Gateway Protocol Developed By The OSPF Working Group Of The Internet Engineering Task Force (IETF). At Present, OSPF Version 2 (RFC2328) Is Used.

Side A	Side B
THREE OSPF TABLES:	1. Neighbor Table – Contains A List Of All Neighboring Routers. 2. Topology Table – Contains A List Of All Possible Routes To All Known Networks Within An Area. 3. Routing Table – Contains The Best Route For Each Known Network.
FIVE TYPES OF OSPF PACKETS:	HELLO DBD (Database Descriptor) - Sends A List Of Router Ids From Whom The Router Has An LSA And The Current Sequence Numberlsr (Link State Request) - Ask For Any Missing LSASlsu (Link State Update) - Replies To Link-State Request With Requested Data.LSAck (Link State Ack) - Confirm Receipt Of Link-State Information
OSPF COST CALCULATION:	COST = 100,000,000/LINKSPEED (100MBPS/LINKSPEED)
EIGHT OSPF NEIGHBOR STATES IN ORDER:	1. Down - No Hello Received From Neighbor. 2. Attempt - Only In NBMA, Sends Unicast Hello. 3. Init - Hello Received, But Receiving Router’s ID Was Not Included In It. 4. 2-Way - Bi-Directional Communication Established. 5. Exstart - Exchanging Link-State Information Can Start Between Routers And DR&BDR. 6. Exchange - Exchange Database Descriptor (DBD). 7. Loading - Exchange Of Link-State Information. 8. Full - Fully Adjacent With Each Other
COMMAND TO: - START OSPF WITH PROCESS NUMBER 100 - ENABLE OSPF AREA 0 ON 10.0.0.0 ints:	ROUTER OSPF 100NETWORK 10.0.0.0 0.255.255.255 AREA 0
THREE POSSIBILITIES TO BE ROUTER ID:	Address Defined By Router-ID Command Highest Loopback Int Address Highest Physical Int Address
COMMAND TO: - DISPLAY OSPF PROCESS DETAILS:	SHOW IP OSPF
COMMAND TO: - DISPLAY CONTENTS OF THE TOPOLOGICAL DATABASE:	SHOW IP OSPF DATABASE
COMMAND TO: - DISPLAY HOW OSPF HAS BEEN CONFIGURED ON EACH INTERFACE:	SHOW IP OSPF INT
COMMAND TO: - DISPLAYS NEIGHBOR INFORMATION (STATE OF ADJACENCIES):	SHOW IP OSPF NEIGHBOR
COMMAND TO: - SHOW IP ROUTING PROTOCOL CONFIGURATION:	SHOW IP PROTOCOLS
COMMAND TO: - DISPLAY ROUTING TABLE:	SHOW IP ROUTE
COMMAND TO: - DISPLAY INFORMATION ABOUT OSPF-RELATED EVENTS, SUCH AS ADJACENCIES, FLOODING INFORMATION, DESIGNATED ROUTER SELECTION, AND SPF CALCULATION:	DEBUG IP OSPF EVENTS
COMMAND TO: - DISPLAY IP DEBUGGING INFORMATION INCLUDES PACKETS RECEIVED, GENERATED, AND FORWARDED:	DEBUG IP PACKET
COMMAND TO: - MANUALLY DETERMINE WHICH ROUTER TO BECOME THE DR:	IP OSPF PRIORITY 100
PARAMETER USED TO CALCULATE THE METRIC:	(100,000,000 BPS DIVIDED BY) SPEED OF THE LINE.
TWO WAYS TO CHANGE METRIC ON INTERFACE:	IP OSPF COST 100IP OSPF AUTO-COST REFERENCE-BANDWIDTH 1000(1000 MEGABYTE PER SECONDS)
TWO COMMANDS TO: - SHOW WHICH ROUTER IS BDR:	SHOW IP OSPF NEIGHBORSHOW IP OSPF INTERFACE
WHAT DOES LSA USE TO RECOGNISE OLDER/NEWER VERSIONS OF ADVERTISEMENT:	SEQUENCE NUMBERS
WHAT SPECIFIES HOW LONG TO WAIT TO START SPF AFTER RECEIVING AN LSA TO PREVENT RUNNING SPF TOO OFTEN:	- SPF SCHEDULE DELAY (FIELD IN SH IP OSPF)
HOW TO SELECT DR:	1. Router With The Highest OSPF Priority 2. If Priority Is Same, Router With Highest RID
OSPF NETWORK TYPES:WHAT ARE TWO RFC-COMPLIANT TYPES?WHAT ARE THREE CISCO-SPECIFIC TYPES:	RFC: - NBMA - Point-to-MultipointCisco: - Point-to-Multipoint no-broadcast - Broadcast - Point-to-point
COMMAND TO: - CONFIGURE OSPF IN NONBROADCAST ENVIRONMENT :	IP OSPF NETWORK {BROADCAST | NON-BROADCAST | {POINT-TO-MULTIPOINT [NON-BROADCAST]}}
WHICH TYPE OF OSPF NETWORK, BROADCAST OR NON-BROADCAST, REQUIES IDENTIFYING/SPECIFYING NEIGHBOUR? COMMAND TO: - IDENTIFY 10.0.0.1 AS NEIGHBOUR:	NON-BROADCAST TYPESNEIGHBOR 10.0.0.1
HOW MANY SUBNETS   REQUIRED IN  OSPF ROUTER WITH MULTIPLE POINT-TO-POINT CONNECTIONS:	ONE SUBNET PER CONNECTION.
OSPF NETWORK TYPES INCLUDE   DR ELECTION:	Multiaccess Topologies, Such As Those Found In NBMA And Broadcast (I.E. NOT Point-To-Something)
WHAT IS DEFAULT HELLO AND DEAD INTERVALS:	30/120 (NBMA, POINT-TO-MULTIPOINT) OR 10/40 (BROADCAST AND POINT-TO-POINT)
WHAT IS DEFAULT OSPF NETWORK TYPE FOR PHYSICAL SERIAL INTERFACES:	NBMA (NonBroadcast MultiAccess)
FOUR OSPF ROUTER TYPES:	1. Internal Router 2. Backbone Router 3. ABR (Area Border Router) 4. ASBR (Autonomous System Boundary Router)
SIX MOST COMMON LSA TYPES:	Type 1: Router Link LSA - Sent By All Routers Type 2: Network Link LSA - Sent By DR Type 3: Network-Summary Link LSA - Sent By ABR Type 4: AS External ASBR Summary Link LSA - Sent By ABR Type 5: External link LSA - sent by ASBR Type 6: MOSPF-LSA - Type 6 LSAs Are Used For Carrying Multicast Routing Information With MOSPF. Cisco Routers Do Not Currently Support Type 6 LSAS. Type7: NSSA external LSA - sent by ASBR in NSSA
FOUR OSPF AREAS ON TOP OF BACKBONE AREA:	1. Standard 2. Stub 3. Totally stub 4. NSSA (Not-So-Stubby Area)
TWO WAYS TO CALCULATE COST TO ANOTHER AREA? WHICH ONE IS DEFAULT:	E1 - Cost Of The Path To ASBR Added To External Coste2 - Only External Cost Of Path From ASBR Considered In Calculatione2 Is Default.
WHAT ARE TWO TYPES OF SUMMARISATION? FOR EACH TYPE: - AT WHICH ROUTER IT HAPPENS? - WHICH LSA TYPES CREATED:	Interarea Summarisation : - Summarise Networks Between Areas  - At ABR  - Creates   Type 3 & 4 LSAsExternal Summarisation:  - Summarize External Networks Sent Into OSPF From Another Routing Protocol  - At ASBR  - Creates Type 5 LSA
COMMAND TO : - START OSPF PROCESS 10 - CONFIGURE INT 172.16.20.128/29 IN AREA 0:	ROUTER OSPF 10NETWORK 172.16.20.128 0.0.0.7 AREA 0
COMMAND TO: - SUMMERISE INTO 172.16.20.128/26 AT ABR  - SUMMERISE INTO 172.16.20.128/26 AT ASBR:	AREA 0 RANGE 172.16.20.128 255.255.255.192 SUMMARY-ADDRESS 172.16.20.128 255.255.255.192
COMMAND TO: - CONFIGURE AREA 1 AS STUB AREA  - CONFIGURE AREA 2 AS TOTALLY STUBBY AREA:	AREA 1 STUB (ABR AND ALL ROUTERS IN THE AREA) AREA 2 STUB NO-SUMMARY (ONLY AT ABR)
COMMAND TO: - SET DEFAULT-COST AT ABR ATTACHED TO STUB AREA 1 (TO DEFINE COST OF A DEFAULT ROUTE PROPAGATED INTO ANOTHER AREA):	AREA 1 DEFAULT-COST 15
COMMAND TO: - CONFIGURE VIRTUAL-LINK THROUGH TRANSIT AREA 1 TO THE OTHER SIDE ROUTER-ID 10.10.10.30:	AREA 1 VIRTUAL-LINK 10.10.10.30
COMMAND TO: - VERIFY ABRS AND ASBRS THAT AN INTERNAL ROUTER HAS IN ITS ROUTING TABLE:	SHOW IP OSPF BORDER-ROUTERS
COMMAND TO: - SHOW CONFIGURED VIRTUAL LINKS:	SHOW IP OSPF VIRTUAL-LINKS
COMMAND: - SIMILAR TO DEBUG COMMANDS BUT USES FEWER RESOURCES:	LOG-ADJACENCY-CHANGES
ROUTES NOT PROPAGATED INTO   A TOTALLY STUBBY AREA:	SUMMARY & EXTERNAL ROUTES (I.E. NO TYPE 3, TYPE 4, OR TYPE 5 LSAS)
WHICH LSAs ABRS FORWARD:	SUMMARY LSAS (I.E. TYPE 3 AND TYPE 4 LSAS)
WHAT IS AN EXTERNAL ROUTE, AND ON WHICH TYPE OF ROUTER WILL THIS ROUTE BE INTRODU:	Route That Did Not Originate In The OSPF Domain, Redistributed From Another Routing Protocol Or Static Routing. Introduced By An ASBR.
MAXIMUM NUMBER OF ROUTERS THAT SHOULD RESIDE IN AN AREA:	40–80
ISSUES TO EMERGE WHEN RUNNING OSPF WITHIN  AREA CONTAINING FRAME RELAY NBMA CLOUD:	Summary LSAs To Be Flooded Throughout The NBMA Network.
HOW DOES STUB AREA DIFFER FROM   BACKBONE AREA:	Stub Area Does Not Propagate External Routes Into Its Area. Backbone Is Obliged To Forward These LSAs.
HOW DOES TOTALLY STUBBY AREA DIFFER FROM STUB AREA:	Stub Area Propagates Neither External Routes Norsummary Routes From Other Areas. Inter Area Connectivity Is Achieved Through The Use Of Default Routes.
WHICH ROUTER TYPE CREATES LSA TYPES 3 AND 4:	ABR
COMMAND TO : - SHOW NETWORK LSA INFORMATION	SHOW IP OSPF [PROCESS-ID AREA-ID] DATABASE NETWORK
WHERE   COMMAND TO   SUMMARISE IP SUBNETS TO BE ISSUED:	AT AREA BOUNDARIES (ABRS OR ASBRs)
WHEN IS APPROPRIATE TO DEFINE   DEFAULT COST FOR THE DEFAULT ROUTE:	When   Stub Area Has More Than One ABR
TYPE OF ROUTER ON WHICH AREA DEFAULT COST DEFINED:	ABR
ON WHICH ROUTER:1) STUB AREA IS CONFIGURED?2) STUB AREA IS CONFIGURED?	1) ABR As Well As ALL Routers Within Stub Area.2) Only On ABR, But All The Other Routers In The Area Must Be Configured As Stub Routers.
COMMANDS TO: - PLACE SUBNETS 144.111.248.0 THROUGH TO 144.111.255.0 IN AREA 1 - PUT ALL OTHER INTERFACES INTO AREA 0:	NETWORK 144.111.248.0 0.0.7.255 AREA 1NETWORK 0.0.0.0 255.255.255.255 AREA 0
COMMAND TO: - SUMMARIZE EXTERNAL SUBNETS 144.111.248.0 TO 144.111.254.255 INTO OSPF :	SUMMARY-ADDRESS 144.111.248.0 255.255.248.0
REASON TO USE LOG ADJACENCY CHANGES RATHER THAN DEBUG:	ISSUE OF RESOURCES
COMMON REASONS THAT NEIGHBORS FAIL TO FORM   ADJACENCY:	Following Are Not Same: - IP Mask  - MTU  - InterfaceHello Timer  - OSPF Hello/Dead Interval.  - Area Type  - Part Of The Same Area
WHICH ROUTERS ARE CONFIGURED FOR VIRTUAL-LINK:	Between The ABRs, Where One Of The ABRs Resides In Area 0 And The Other In The Area That Is Disconnected From The Backbone Router
OSPF AREA TYPES WHICH PERMIT LSA TYPE 1 AND 2:	ALL (STANDARD, STUB, TOTALLY STUBBY, AND NSSA).
OSPF AREA TYPES WHICH PERMIT LSA TYPE 3 AND 4:	All Except Totally Stubby.
OSPF AREA TYPE WHICH PERMITS TYPE 5:	Standard
WHAT IS OSPF LSA TYPE 7:	Temporary LSA Assigned To Routes Redistributed By ASBR Attached To   NSSA.
WHAT IS PROBLEM WITH MULTIPLE ABRS IN TOTALLY STUBBY AREA :	The Only Path Out Of The Area Is Via   Default Route, Which May Be Suboptimal Should There Be Multiple Exit Points.
WHICH AREA TYPES PERMIT VIRTUAL-LINK:	Standard, Non-Backbone Areas.
WHY MUST INTERNAL ROUTERS IN STUB AREA BE IDENTIFIED AS STUB:	All Internal Routers In Stub Area Must Have This Same Command So That All Hellos Agree On Stub Area Flag.
WHAT IS MESSAGE DIGEST:	A Hash Value Used To Secure   Password.
HOW DO ASBR ROUTES APPEAR IN   ROUTING TABLE INSIDE   NSSA:	N1/N2(Instead of E1/E2)

For Reference :

Differences Between OSPFv2 & OSPFv3 :

OPEN SHORTEST PATH FIRST SHORT NOTES (OSPF):

OSPF QUICK REFERENCE :

OSPF Quick Reference Table:

CISCO - OSPF Commands Reference :

CISCO - OSPF Configuration Examples :