OSPF Lecture Day

I use this topology as my OSPF lecture day 1. Estimated lecture hours take 2 hours and 40 minutes.  Enjoy Studying.

 

OSPF Route Filtering Exercise 2

Answer
----------
R1#
!
router ospf 1
 log-adjacency-changes
 no auto-cost
 network 10.1.12.1 0.0.0.0 area 0
 network 10.1.15.1 0.0.0.0 area 15
 network 10.1.21.1 0.0.0.0 area 0
 distribute-list 1 in FastEthernet0/0
 distribute-list 2 in FastEthernet2/0
!
!
access-list 1 deny   3.3.3.3
access-list 1 permit any
access-list 2 deny   4.4.4.4
access-list 2 permit any
!

OSPF Route Filtering Exercise 1

Verfication Tasks
----------------------
R1 - show ip route ospf
R1 - show ip ospf database
R5 - show ip route ospf
R5 - show ip ospf database
`

BGP versus OSPF/ISIS

This is good enough for your interview. But the below slides will be more easy to understand if you had working experience in IXP Environment before.




Reference : Cisco Systems, Inc.
~~

OSPF E1 vs E2

This is OSPF E1 vs E2 in a nutshell.

Fig : OSPF E1 vs E2

Studying OSPF Stub & Totally Stubby Area

As usual, this note is also in visio format. Please don't forget that I love drawing :-)

It really helps me when I need to go for an interview :-)

Fig1 : Topology Diagram

Fig2 : OSPF Stub Area

Fig3 : OSPF Stub Area

Fig4 : OSPF Stub Area

Fig5 : OSPF Stub Area

Fig6 : OSPF Totally Stubby Area

Fig7 : OSPF Totally Stubby Area

OSPF Stub Area

We all know how to configure an OSPF Stub Area. It can be done with just one command. But, the points I wanna share with you here are from Network Planning Point of View (or) when you need to make a presentation to your customer about some parts of your current operational OSPF area will migrate to an OSPF Stub Area. The points we should include in our presentation are :

- What types of LSAs are not being originated within stub area;
- The Hellos originated by the router into the stub area will have E=0 in the
Options field;
- Existing OSPF adjacency will be broken;
- *Downtime should be scheduled because routing will be disrupted until all routers
are reconfigured as stub area ;
- Verify/Prove that the size of the OSPF database has been reduced;

*The most important fact we have to plan/highlight to the customer is.

I feel that we need to know those facts rather than just typing the command.

Reference : Routing TCP/IP Volume 1, Second Edition ; Page 423

OSPF Virtual-Link vs GRE Tunnel

This is my note for OSPF Virtual-Link vs GRE Tunnel.
I don't realize that the clock strikes to 2:40AM SGT (6/Nov/2010) ...
Well, I'm gonna go to sleep ... ^_^

Fig : OSPF Virtual-Link vs GRE Tunnel

Troubleshooting OSPF P2M vs Frame-Relay

Fig : Troubleshooting OSPF P2M vs Frame-Relay ( 1 / 3 )

Fig : Troubleshooting OSPF P2M vs Frame-Relay ( 2 / 3 )

Fig : Troubleshooting OSPF P2M vs Frame-Relay ( 3 / 3 )

2WAY/DROTHER

Here I am going to test about what 2WAY/DROTHER State in OSPF is based on shown topology.
I configure the R1 ospf priority as 255 (DR) and R2 ospf priority as 254 (BDR).
Let's examine the output.

From R1(DR) point of view,
R2 will be FULL/BDR and the rest will be FULL/DROTHER state.

From R2(BDR) point of view,
R1 will be FULL/DR and the rest will be FULL/DROTHER state.

Here we go and see 2WAY/DROTHER State from R3,R4,R5,R6,R7 and R8 point of views. The routers which are not DR/BDR (here is R3,R4,R5,R6,R7 and R8) will see each other in 2WAY/DROTHER State. But they see the R1(DR) as FULL/DR and R2(BDR) as FULL/BDR.

Why 2WAY/DROTHER State ? Here is the Q and A from Cisco OSPF FAQ Website.

Q. When I issue the show ip ospf neighbor command, why do I only see FULL/DR and FULL/BDR, with all other neighbors showing 2WAY/DROTHER?

A. To reduce the amount of flooding on broadcast media, such as Ethernet, FDDI, and Token Ring, the router becomes full with only designated router(DR) and the backup designated router(BDR), and it shows 2-WAY for all other routers.

The question I was asked about OSPF

At interview,
1. Does your OSPF router-id need to be a reachable IP address ?
The answer is NO.

2. Can we set 239.1.1.1 as OSPF router-id?
The answer is YES.

3. Cisco OSPF Network Types and RFC Network Types? :)
Non-Broadcast > RFC2328
Broadcast > Cisco
Point-to-Point > Cisco
Point-to-Multipoint > RFC2328
Point-to-Multipoint Non-Broadcast > Cisco

4. Is Area 1 equal to Area 1.1.1.1 ?
The answer is NO.
Area1 = Area 0.0.0.1
Area0 = Area 0.0.0.0