Introduction to OSPF

Lessons Discussion
81

Hi,

I was trying the lab on gns3 and the image is cisco IOSv ,

Why cost is 1000 here , it should be 10 right ?

interface GigabitEthernet0/0
 bandwidth 100
 ip address 192.168.12.2 255.255.255.0
 duplex auto
 speed auto
 media-type rj45
end

-

spade#sh ip ospf interface gi0/0
GigabitEthernet0/0 is up, line protocol is up
  Internet Address 192.168.12.2/24, Area 0, Attached via Network Statement
  Process ID 10, Router ID 2.2.2.2, Network Type BROADCAST, Cost: 1000

Thanks

82

Dear Sims,

To know what is your reference bandwidth, you can issue this command:

R2#show ip ospf | include Reference
 Reference bandwidth unit is 100 mbps

As explained in this lesson:
cost = reference bandwidth / interface bandwidth

If you want that your cost becomes 10, then you have to change your Reference bandwidth or the bandwidth on your interface.
To change the reference bandwidth, you can use this command:

Router(config-router)#auto-cost reference-bandwidth ?
  <1-4294967>  The reference bandwidth in terms of Mbits per second

I highly advice that you read this lesson for more information:

OSPF Reference Bandwidth

Hope this can help.

83

OSPF was never so easy ! Thanks a ton

84

You are welcome Abhishek :slight_smile:

85

Hello Rene,

I’m from Βelgium and so happy to find you today.
You have got some great comments to thank you. But I must say too, you did an amazing job.
I was searching for a long time a great lessons site like yours because netacad has got really too much “blabla” and importants things are not always easy to memorize. It’s my first 1€ day but I am happy to spend my money to be a good network engineer working on here for next months. Thank you for your good job.

Niko
from Luik-Liège-Luttich

86

Dear Niko,

Thanks for your kind words, they have been forwarded to Rene.

Best luck in your study and in your career.

87

Hi Rene,
Your explanation is the best, this is my personal opinion. Thank you for your job.

88

Rene, Im actually seeing you typed as “These are out of CCNA so you are skipping this part” , Actually for me i selected CCNP route & reading all these stuffs…Are you saying that the details above is for CCNA Folks…?

89

WOW, I know so many Network books and blogs (yep, I read all Odom books, Bryant and NetworkWarrior) but this page is a cool refresher and very well explained.

90

Hello Ajay!

Just so you know, the topics covered in this OSPF lesson are necessary to pass the CCNA exam, however, they are also a good referesher for you as you study for your CCNP as well. CCNP will require you to build upon these principles as OSPF and routing protocols in general are a large part of the CCNP exams…

I hope this has been helpful!

Laz

91

Hii Rene,
I think ASBR stands for Autonomous system boundary router…Please correct me if i am wrong…

92

Hello Raj

Yes, you are absolutely correct!

Laz

93

Hello Rene,

thanks for this website, it’s awesome.
I’ve already done my CCNA certification, but is always good to refresh my knowledge :wink:

Do you plan any wireless courses in the future?

S.

94

Hi @stanislavpilat ,

Glad to hear you like it. I do have plans for wireless sometime. I used to teach CWNA/CWNP every now and then in the classroom before I worked on networklessons.com.

Rene

95

19 posts were merged into an existing topic: Introduction to OSPF

96

Hi Rene,

Hope you are doing great . I am facing a problem in my production network regarding OSPF Load Balancing . From the Routing table I have found 2 path(1G+1G) of OSPF to reach a certain Destination but one link carrying 700MB and another link 100MB. So , How its happening ?? There is simple OSPF configuration . I cant understand the issue . From the begining I know that OSPF doing 50/50 load Balance . Dear Please help me to understand this . Appreciate your cooperation as always .Many Thanks

br/zaman

97

Hello Mohammad

If you have two different routes to the same destination both learned via OSPF that have the same metric, then both will be installed into the routing table. As you said, OSPF does equal load balancing. Having such an unequal cost occurring is strange. However, ask yourself the following questions and see if these help:

How are you determining the amount of data carried by each link? Are you sure that the data contained within both the 700MB and the 100MB over each link have the specific destination? Do other routes in the routing table use the first interface (carrying 700MB) for their routing purposes as well and are adding data to it?

Check to make sure that the bandwidth parameter on all interfaces between the source and destination are configured correctly. It could be that the total bandwidth for both routes is the same, however, there may be a bottleneck on one of the routes that is not allowing packets through.

I hope this has been helpful and that it will give you a starting point for your troubleshooting to solve your problem.

Laz

98

Hi Laz,

Thanks for your valuable information. I have checked all possible reason that you mention but there is no issue like this. Would you please LAB this issue and verify why this happening ?

br/zaman

99

Hello Mohammad.

In order to help you out more, can you answer the following questions?

How are you determining the amount of data carried by each link? What are there bandwidths of the links to the destination downstream for each of the two possible links? How many hops for each route to reach the destination network? Are there other OSPF routes that use the same exit interfaces that may be skewing the data?

I look forward to hearing from you.

Laz

100

Hi,
Im new in OSPF I have a question.
I have two routers that have fiber links for redundancy one of them is connected to the firewall that has connected internet links so on that router I will configured the “default-information originate always” command so the users that are connected to the other routers can have access to the internet.

That router also is the Core of the network so I have to advertised all the networks connected to it.
Can I use the redistribute static subnets? If I want to advertised all the connected networks does I have to use the passive interface on in that case doesn´t apply because all the networks are going to be redistributed?

Thanks for your reply