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#1 DarkFiber

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Posted 26 April 2009 - 08:59 AM

OSPF

OSPF Summary

The characteristics of OSPF follow:

 Link-state routing protocol.
 Uses Dijkstra algorithm to calculate SPF tree, which is Built around a well-known algorithm from graph theory, E. W. Dijkstra's shortest path algorithm.

 Uses IP protocol 89.

 Classless protocol (supports VLSMs and CIDR).

 Metric is cost, based on interface bandwidth by default (10^8 / BW in bps).

 Sends partial route updates only when there are changes.

 Use LSA messages, LSA are sent in a Sequence manner. ( sequence number )

 Send hello packets every 10 sec with dead timer of 40 sec over P-P & BC networks.

 Send hello packets every 30 sec with dead timer of 120 sec over NBMA networks.

 If the network is stable and there have been no updates within 30 min (LSRefreshTime), a compressed update is sent.

 MaxAge (60 min), LSRefreshTime (30 min) and MaxAgeDiff (15 min) are OSPF architectural constants.

 LSRefreshTime is used to reset the MaxAge timer.

 The numbering scheme is a 4-byte number that begins with 0x80000001 and ends with 0x7FFFFFFF.

 Routes labeled as intra-area, interarea, external Type 1, or external Type 2.

 Support for authentication.

 Default administrative distance is 110.

 Uses multicast address 224.0.0.5 (ALLSPFRouters).///mac adresss

 Uses multicast address 224.0.0.6 (ALLDRouters). ).///mac adresss

 The reply for the hello is done in a unicast way./////////

 Up to 16 Links for load balance, Over equal Cost metric for same paths type default is 4 paths

 Recommended for large networks.

 For 2 routers to be adjacent :
1st. Hello packets must be sent & received.
2nd They must have the same hello & dead timers
also same Net ID with subnet mask.
3rd They must be in the same area.


Check attachment for more info.
Hope it might help

Attached Files


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#2 DarkFiber

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Posted 30 April 2009 - 08:20 AM



Hello Guys , any questions regarding this Topic : )
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#3 martinlo

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Posted 30 April 2009 - 12:02 PM

QUOTE (DarkFiber @ Apr 29 2009, 05:20 PM) <{POST_SNAPBACK}>
Hello Guys , any questions regarding this Topic : )

You are missing 2 additional factors when OSPF becomes neighbors according to W. Odom's ICDN2 CiscoPress-CCNA-level book.
One of them is on CCNA Test, so It is very IMPORTANT.

Edited by martinlo, 30 April 2009 - 12:03 PM.

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#4 kIdMaN

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Posted 30 April 2009 - 02:58 PM

QUOTE (martinlo @ Apr 30 2009, 05:02 AM) <{POST_SNAPBACK}>
You are missing 2 additional factors when OSPF becomes neighbors according to W. Odom's ICDN2 CiscoPress-CCNA-level book.
One of them is on CCNA Test, so It is very IMPORTANT.


Friend martinlo,,,

OSPF in CCNP is different! the concepts are same, but the discussion is in depth and very detailed, so the initial things like "forming neighborship" steps are discussed at the very beginning of the OSPF chapters and it should be known very well before in depth discussion. Maybe thats why DF didn't mention it.



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#5 kIdMaN

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Posted 30 April 2009 - 03:03 PM

I forgot to mention; don't miss to download the attached file, its useful and contain what you asked about.

Thanks to DF.
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#6 martinlo

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Posted 30 April 2009 - 03:15 PM

QUOTE (kIdMaN @ Apr 29 2009, 11:58 PM) <{POST_SNAPBACK}>
Friend martinlo,,,

OSPF in CCNP is different! the concepts are same, but the discussion is in depth and very detailed, so the initial things like "forming neighborship" steps are discussed at the very beginning of the OSPF chapters and it should be known very well before in depth discussion. Maybe thats why DF didn't mention it.

Oh, ya, thanks for reminding me. it is missing in his OSPF, SPF your LIFE - CCNA post as well.
I will check .doc again, but I think it is NOT there as well.
Any one else spot missing requirement?
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#7 DarkFiber

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Posted 30 April 2009 - 05:27 PM

QUOTE (martinlo @ Apr 30 2009, 08:15 AM) <{POST_SNAPBACK}>
Oh, ya, thanks for reminding me. it is missing in his OSPF, SPF your LIFE - CCNA post as well.
I will check .doc again, but I think it is NOT there as well.
Any one else spot missing requirement?


Martinlo , Kindly post the missing requirement that you advised, so we can share it with our friends here smile.gif

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#8 martinlo

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Posted 30 April 2009 - 06:50 PM

QUOTE (DarkFiber @ Apr 30 2009, 02:27 AM) <{POST_SNAPBACK}>
Martinlo , Kindly post the missing requirement that you advised, so we can share it with our friends here smile.gif

authentication (if configured) must match on routers.

both OSPF and EIGRP use authentication to secure network. otherwise, an attacker connects a rouge router to the network and can easily cause a denial-of-service (DoS) attack and/or reconnaissance attacks.

attachment lists requirements for OSPF and EIGRP

Attached File  Neigbour_req._OSPF_and_EIGRP.JPG   47.66KB   424 downloads
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#9 kIdMaN

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Posted 30 April 2009 - 07:07 PM

QUOTE (martinlo @ Apr 30 2009, 11:50 AM) <{POST_SNAPBACK}>
authentication (if configured) must match on routers.

both OSPF and EIGRP use authentication to secure network. otherwise, an attacker connects a rouge router to the network and can easily cause a denial-of-service (DoS) attack and/or reconnaissance attacks.

attachment lists requirements for OSPF and EIGRP

Attached File  Neigbour_req._OSPF_and_EIGRP.JPG   47.66KB   424 downloads


1- I think you need to download a read the attached file first. Authentication and how to configure it is already mentioned their.
2- Those topics are considered to be a "NOTES" not references. It is glimpses and reminders.

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#10 martinlo

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Posted 30 April 2009 - 07:40 PM

QUOTE (kIdMaN @ Apr 30 2009, 04:07 AM) <{POST_SNAPBACK}>
1- I think you need to download a read the attached file first. Authentication and how to configure it is already mentioned their.
2- Those topics are considered to be a "NOTES" not references. It is glimpses and reminders.

Yes it is mentioned, but not where is important.

QUOTE
For 2 routers to be adjacent :
1st. Hello packets must be sent & received.
2nd They must have the same hello & dead timers
also same Net ID with subnet mask.
3rd They must be in the same area.


All requirements must be fulfilled or relationship fails. That is ALL; not 3 of 4 or 4 of 5; get it? All.
How can you create relationship when you missing one of requirements?
if your notes have holes (incomplete), good luck studying technology, passing exam, or troubleshoot at work!
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#11 kIdMaN

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Posted 30 April 2009 - 07:44 PM

QUOTE (martinlo @ Apr 30 2009, 12:40 PM) <{POST_SNAPBACK}>
Yes it is mentioned, but not where is important.

All requirements must be fulfilled or relationship fails. That is ALL; not 3 of 4 or 4 of 5; get it? All.
How can you create relationship when you missing one of requirements?
if your notes have holes (incomplete), good luck studying technology, passing exam, or troubleshoot at work!


Ok, i agree with you, so could you please state ALL the requirements needed in order to have OSPF neighborship?
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#12 DarkFiber

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Posted 30 April 2009 - 08:56 PM

QUOTE (martinlo @ Apr 30 2009, 12:40 PM) <{POST_SNAPBACK}>
Yes it is mentioned, but not where is important.

Taken from my attached OSPF file here
Notes: passwords & key ID must be the same between neighbors, and all area must support authentication, as authentication if enabled it must be enabled on the entire area.
Still OSPF doesn’t support key-chain config till the time of this writing.


Why the hell could some one authenticate only one side neighbor and leave the other, ofcorse it wont work, that's ABC design.
And YES its NOT an important requirement , or a Default requirment Unless you use the optional Authentication OSPF feature wink.gif

END OF STORY smile.gif


QUOTE (martinlo @ Apr 30 2009, 12:40 PM) <{POST_SNAPBACK}>
All requirements must be fulfilled or relationship fails. That is ALL; not 3 of 4 or 4 of 5; get it? All.
How can you create relationship when you missing one of requirements?
if your notes have holes (incomplete), good luck studying technology, passing exam, or troubleshoot at work!


MAN, are you talkn to me ?

Edited by DarkFiber, 30 April 2009 - 08:59 PM.

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#13 syed abid ali

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Posted 30 April 2009 - 10:02 PM

Thanks a lot!!! ........very good doc on EIGRP & OSPF
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#14 martinlo

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Posted 01 May 2009 - 08:30 AM

QUOTE (DarkFiber @ Apr 30 2009, 02:27 AM) <{POST_SNAPBACK}>
Martinlo , Kindly post the missing requirement that you advised, so we can share it with our friends here smile.gif


Besides authentication (optional), what about IP MTU?

All requirements are matching except IP MTU, will two routers become neighbors or not?

I am talking to everybody who wants to be CCNA. Pay attention to details!
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#15 upen singh

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Posted 01 May 2009 - 09:33 AM

You can find that info. in various books and study materials

Thanks
Upen


QUOTE (syed abid ali @ Apr 30 2009, 11:02 PM) <{POST_SNAPBACK}>
Thanks a lot!!! ........very good doc on EIGRP & OSPF


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#16 DarkFiber

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Posted 01 May 2009 - 10:38 PM

QUOTE (martinlo @ May 1 2009, 01:30 AM) <{POST_SNAPBACK}>
Besides authentication (optional), what about IP MTU?

All requirements are matching except IP MTU, will two routers become neighbors or not?

I am talking to everybody who wants to be CCNA. Pay attention to details!



NOW WE CAN TALK

The IP MTU Must match for new IOS versions, between neighbors, by default is the same on all routers, so it wasn't an issue, but after introduction of Multi-layer switches, the problem started.
when u configure OSPF between a router & a switch, OSPF neighbor didn't come up, as MTU value is different

So you must adjust the IP MTU to be the same, But Cisco made another thing, A cmd that will make the OSPF neighbors ignore the MTU wink.gif

Config-if)# ip ospf mtu-ignore


@martinlo , I have this info in my documents , but for the CCIE section smile.gif

For 2 routers to be adjacent :
1st. Hello packets must be sent & received.
2nd They must have the same hello, dead timers
same Net ID with subnet mask & equal MTU on both side
3rd They must be in the same area.

Edited by DarkFiber, 01 May 2009 - 10:40 PM.

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#17 pappyaar

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Posted 02 May 2009 - 12:01 AM

QUOTE (DarkFiber @ May 1 2009, 11:38 PM) <{POST_SNAPBACK}>
NOW WE CAN TALK

The IP MTU Must match for new IOS versions, between neighbors, by default is the same on all routers, so it wasn't an issue, but after introduction of Multi-layer switches, the problem started.
when u configure OSPF between a router & a switch, OSPF neighbor didn't come up, as MTU value is different

So you must adjust the IP MTU to be the same, But Cisco made another thing, A cmd that will make the OSPF neighbors ignore the MTU wink.gif

Config-if)# ip ospf mtu-ignore


@martinlo , I have this info in my documents , but for the CCIE section smile.gif

For 2 routers to be adjacent :
1st. Hello packets must be sent & received.
2nd They must have the same hello, dead timers
same Net ID with subnet mask & equal MTU on both side
3rd They must be in the same area.


Hi all. Well there are two points which are being neglected from the very start.

First regarding adjacency.

For P2P and P2MP links ONLY THE SUBNET ID NEEDS TO BE SAME AND NOT THE MASK. IF THE MASK IS SAME, ITS FINE, IF ITS NOT ITS FINE AGAIN :-)
For Broadcast and non broadcast networks (involving DR) the subnet mask and ID must both be same !!.

Now regarding the MTU.

This is often misleading. Ip ospf mtu ignore may get you to 2WAY state but no more then that. Sometimes it works and sometimes it doesnt. You will see situations when even running this command will not relieve routers from their exchange hangning state. The only solution that i can think of is to determine the exact mtu of either side and configure it.

How to determine the MTU of a path ?

Well we can use ping command with DF bit set and gradually increasing the byte by increments of 100 and 200 so a point will come the ping will not be responded. A bit more close examination will help you determine the exact mtu of the link.

If you guys are interested then i will surely be telling a real life case i faced 2 weeks ago where adjacency wasnt coming up even after mtu ignore.

Hope this helps

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#18 DarkFiber

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Posted 02 May 2009 - 01:57 AM

QUOTE (pappyaar @ May 1 2009, 05:01 PM) <{POST_SNAPBACK}>
Hi all. Well there are two points which are being neglected from the very start.

First regarding adjacency.

For P2P and P2MP links ONLY THE SUBNET ID NEEDS TO BE SAME AND NOT THE MASK. IF THE MASK IS SAME, ITS FINE, IF ITS NOT ITS FINE AGAIN :-)
For Broadcast and non broadcast networks (involving DR) the subnet mask and ID must both be same !!.

Now regarding the MTU.

This is often misleading. Ip ospf mtu ignore may get you to 2WAY state but no more then that. Sometimes it works and sometimes it doesnt. You will see situations when even running this command will not relieve routers from their exchange hangning state. The only solution that i can think of is to determine the exact mtu of either side and configure it.

How to determine the MTU of a path ?

Well we can use ping command with DF bit set and gradually increasing the byte by increments of 100 and 200 so a point will come the ping will not be responded. A bit more close examination will help you determine the exact mtu of the link.

If you guys are interested then i will surely be telling a real life case i faced 2 weeks ago where adjacency wasnt coming up even after mtu ignore.

Hope this helps


To be honest i never faced a situation where the mtu-ignore cmd didn't work , I always apply it on both sides to be sure...loool
Kindly advise your real life example, so we can share our experience...thanks in advance smile.gif

Regarding the MU path discovery , you wont use it for OSPF , as OSPF is between 2 Directly connected neighbors.
But for other troubleshooting & applications, Yes this is a great & smart Idea to detect the Largest MTU you can use.
I used to use this idea in troubleshooting several years ago.


STARTING TO FEEL THAT NEW CCNP GUYS WILL RULE THE WORLD SOON......

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#19 pappyaar

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Posted 02 May 2009 - 05:11 AM

QUOTE (DarkFiber @ May 2 2009, 02:57 AM) <{POST_SNAPBACK}>
To be honest i never faced a situation where the mtu-ignore cmd didn't work , I always apply it on both sides to be sure...loool
Kindly advise your real life example, so we can share our experience...thanks in advance smile.gif

Regarding the MU path discovery , you wont use it for OSPF , as OSPF is between 2 Directly connected neighbors.
But for other troubleshooting & applications, Yes this is a great & smart Idea to detect the Largest MTU you can use.
I used to use this idea in troubleshooting several years ago.


STARTING TO FEEL THAT NEW CCNP GUYS WILL RULE THE WORLD SOON......


Dear Dark, i am not a ccnp and i never will be ;-). this post might be a bit long....

I was looking at my hub router's logging for some other issue and i realized that one of my branch was flapping between exchange to down. I knew that i have to run ospf ignore so simply passed. It was a wimax link and we are asked by the ISP to configure mtu of 14oo on our links. To further confuse the matter there were some branches that didnt had this mtu configured but still were working fine !!!.

Day 1.

I logged on the router and checked the command on both side. Hub and branch. both has mtu ignore configured but the status was confusing. On hub it was exstart and on branch it was exchange. I knew it had to do mtu so i manually configured it but no success. Now i blindly configured it on tunnel interface still no success. I knew it was ISP issue and i have to consult them but i thought why shouldnt make it working by myself if i think i am an ospf expert (i just think i am, but i am not ;-) ). I left it since i was getting late.

Day 2.

I again logged on, tried everything to take it to full state and it was successful but over that wimax link nothing was working. Only the adjacecny was in full state but i could take dame ware session, ssh session so this further confirms my point that it was mtu issue. I read somewhere that DBD packets (process during exhange/exstart state) had DF bit set to 1. Later i checked and it wasnt but i still tried setting the DF bit to 0 but still no success.

It was time for drastic action ;-).

I opened another wimax branch with exactly same configuration. means
Same IOS
Same router 1841
link was terminated on HWIC 4ESW and ip was given on Vlan 1. Mtu was to be 1400

I ping the hub address from the working branch with DF bit set to 1 and size set to 1400. Ping was successful
I ping the hub with DF bit set to 1 and size set to 1401, and PING WAS UNSUCCESSFUL.

This proved my point so i tried the same thing on troubled branch.
I ping with DF bit set to 1 and size of 1300, it was failed
i pinged with 1000 DF set to 1 and ping failed
i pinged with 500 and it succeded !!!!
i pinged with 550 and it was failed again.

Interesting part:

I went to interface and you will not believe it, the moment i entered ip mtu 500, adjacecny come up !!!!. Everything was working fine now on that link ;-).
I called the ISP and they admitted it was their issue and resolved it in approx half hour.

And they lived happily every after ;-)
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#20 DarkFiber

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Posted 02 May 2009 - 11:49 AM

QUOTE (pappyaar @ May 1 2009, 10:11 PM) <{POST_SNAPBACK}>
Dear Dark, i am not a ccnp and i never will be ;-). this post might be a bit long....

I was looking at my hub router's logging for some other issue and i realized that one of my branch was flapping between exchange to down. I knew that i have to run ospf ignore so simply passed. It was a wimax link and we are asked by the ISP to configure mtu of 14oo on our links. To further confuse the matter there were some branches that didnt had this mtu configured but still were working fine !!!.

Day 1.

I logged on the router and checked the command on both side. Hub and branch. both has mtu ignore configured but the status was confusing. On hub it was exstart and on branch it was exchange. I knew it had to do mtu so i manually configured it but no success. Now i blindly configured it on tunnel interface still no success. I knew it was ISP issue and i have to consult them but i thought why shouldnt make it working by myself if i think i am an ospf expert (i just think i am, but i am not ;-) ). I left it since i was getting late.

Day 2.

I again logged on, tried everything to take it to full state and it was successful but over that wimax link nothing was working. Only the adjacecny was in full state but i could take dame ware session, ssh session so this further confirms my point that it was mtu issue. I read somewhere that DBD packets (process during exhange/exstart state) had DF bit set to 1. Later i checked and it wasnt but i still tried setting the DF bit to 0 but still no success.

It was time for drastic action ;-).

I opened another wimax branch with exactly same configuration. means
Same IOS
Same router 1841
link was terminated on HWIC 4ESW and ip was given on Vlan 1. Mtu was to be 1400

I ping the hub address from the working branch with DF bit set to 1 and size set to 1400. Ping was successful
I ping the hub with DF bit set to 1 and size set to 1401, and PING WAS UNSUCCESSFUL.

This proved my point so i tried the same thing on troubled branch.
I ping with DF bit set to 1 and size of 1300, it was failed
i pinged with 1000 DF set to 1 and ping failed
i pinged with 500 and it succeded !!!!
i pinged with 550 and it was failed again.

Interesting part:

I went to interface and you will not believe it, the moment i entered ip mtu 500, adjacecny come up !!!!. Everything was working fine now on that link ;-).
I called the ISP and they admitted it was their issue and resolved it in approx half hour.

And they lived happily every after ;-)


That's wired, but some times funny things happens..........

One of my night shift working days , i was logging to a router to make troubleshooting on it, and guess what .........after couple of min the router started popping this logs

PPQC123#readread read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read
PPQC123#
PPQC123#
PPQC123#read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read read

So i was shocked, i told my self, did it really happened, i know that there are ppl who can listen & understand to Trees , animals...but not routers...loool.......did GOD gave me a gift that i can talk & understand what routers can say !!!!!
May be the router was telling me , read the IOS bugs 1st your peace of sh*t...loool



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#21 thead

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Posted 05 May 2009 - 04:04 AM

Hi i just want to thank you for your work on topics that summarizes these technologies(RIPv2,IP multicas,OSPF,EIGRP), they are really handy wink.gif

Cheers
Thead
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#22 RAJESH CCIE

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Posted 15 July 2009 - 12:30 AM

DarkFiber I really like you OSPF CCNP DOC Can you please provide me the same DOC for BGP and IPS,

As i am going to appear for CCIE SEcurity LAb this years help me out for that

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#23 DarkFiber

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Posted 15 July 2009 - 08:03 PM

QUOTE (RAJESH CCIE @ Jul 14 2009, 05:30 PM) <{POST_SNAPBACK}>
DarkFiber I really like you OSPF CCNP DOC Can you please provide me the same DOC for BGP and IPS,

As i am going to appear for CCIE SEcurity LAb this years help me out for that


Thanks , will be doing it in Spetember, as my CCIE SP LAB is next month sad.gif

Also im not good in IPS

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#24 Migael

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Posted 16 July 2009 - 02:00 AM

DarkFiber, if I'm running OSPF on a router and I have 2 networks on one interface but I only want to advertise one of them, what is the best way to do it?

Thanks.

Edited by Migael, 16 July 2009 - 02:00 AM.

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#25 DarkFiber

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Posted 16 July 2009 - 08:12 AM

QUOTE (Migael @ Jul 15 2009, 07:00 PM) <{POST_SNAPBACK}>
DarkFiber, if I'm running OSPF on a router and I have 2 networks on one interface but I only want to advertise one of them, what is the best way to do it?

Thanks.


config-if)# ip add <>
config-if)# ip add <> secondary
config-if)# ip ospf <process #> area <#> secondaries none

Use this cmd, to enable OSPF explicitly on an interface & secondary none word is used to Prevents secondary IP addresses on the interface from being advertised

Tell me if you need any thing more wink.gif

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#26 Migael

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Posted 17 July 2009 - 05:10 AM

QUOTE (DarkFiber @ Jul 15 2009, 06:12 PM) <{POST_SNAPBACK}>
config-if)# ip add <>
config-if)# ip add <> secondary
config-if)# ip ospf <process #> area <#> secondaries none

Use this cmd, to enable OSPF explicitly on an interface & secondary none word is used to Prevents secondary IP addresses on the interface from being advertised

Tell me if you need any thing more wink.gif


Awesome. Thanks. If I wanted to go a step further and I had 4 IPs on the interface, but I only wanted to advertise 2, is there a way to do that also?
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#27 DarkFiber

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Posted 17 July 2009 - 07:38 AM

QUOTE (Migael @ Jul 16 2009, 10:10 PM) <{POST_SNAPBACK}>
Awesome. Thanks. If I wanted to go a step further and I had 4 IPs on the interface, but I only wanted to advertise 2, is there a way to do that also?


hmmm....teh command i advised you will block all the secondary IPs , even if you have 10 secondary IPs, they will be all blocked.

You may not use this command, and do a filter-list to filter all the un needed LSAs, hope you want to advertise them across area's.
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#28 Routraxx

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Posted 30 July 2009 - 06:20 AM

Hi Friends,

Good to know that ppl are diving into concepts rather than braindumping them....awesome...Now for the OSPF neighbor relationships...

Following are the parameters i feel, must match for a neighbor relationship to form in OSPF:-


1) Hello and dead timers
2) Authentication password(MD5) if configured
3) Area id
4) MTU (take care during multi vendor scenario)
5) Subnet mask
6) Stub area flag if its a stub area configuration


And remember there's a logical AND between above parameters..... ;)
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#29 Jamalus

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Posted 31 July 2009 - 11:27 PM

Following are the parameters i feel, must match for a neighbor relationship to form in OSPF:-
1) Hello and dead timers
2) Authentication password(MD5) if configured
3) Area id
4) MTU (take care during multi vendor scenario)
5) Subnet mask
6) Stub area flag if its a stub area configuration
And remember there's a logical AND between above parameters..... ;)

You forgot:

7) K-values
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#30 param

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Posted 02 August 2009 - 05:45 PM

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