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Doyle Vol 1 conflicts with RFC 2328 (OSPF) ?

Answered Question
Apr 26th, 2006
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Hi,

Jeff Doyle (TCP/IP) vol 1 states that the adjacency building process uses 3 types of OSPF packets:


Database Description (type 2)

Link State Request (type 3)

Link State Update (type 4)


However, RFC 2328 States that adjacencies are formed by Type 2 and Type 3 only. Can I take this as an error by Doyle ?


Phil.

Correct Answer by pkhatri about 11 years 3 months ago

Actually Vlad, LS Acks are not used in the Database Exchange process. Each router places all requested LSAs in the LSA Request List. As LS Updates are received, LSAs in the LSA Request List. If an LSA has not been received, the LS Request packet will be re-transmitted.


As such, LS Acks are not used here but they are certainly used as part of the reliable flooding mechanism.


I would appreciate you rating the post if it helps.


Paresh

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pkhatri Wed, 04/26/2006 - 18:54
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Doyle is absolutely correct here. Where does RFC2328 say that only type 2 and 3 packets are used for adjacency formation ? I don't see that in RFC2328 at all...


I would appreciate you rating the post if it helps.


Paresh

vladrac-ccna Wed, 04/26/2006 - 18:57
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Hello Paresh,


I believe he was not talking about LSA types, but OSPF packet types.


Vlad

pkhatri Wed, 04/26/2006 - 19:00
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As always, thanks to you Vlad - I've fixed that post now :-)

pkhatri Wed, 04/26/2006 - 19:03
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Phil,


If you check out section 10.10 of RFC2328, there is an example of adjacency formation. It clearly shows the use of the followiing packet types:

- Database Description

- LS Request

- LS Update


I would appreciate you rating the post if it helps.


Paresh

vladrac-ccna Wed, 04/26/2006 - 19:09
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This is the kind of pure theory question, that wont affect much of your understanding of the OSPF routing protocol I guess.


Because for my conception, even "The Link State Acknowledgment packet" would be part of this, as this packets need to be acknowlegded.


Vlad

Correct Answer
pkhatri Wed, 04/26/2006 - 19:13
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Actually Vlad, LS Acks are not used in the Database Exchange process. Each router places all requested LSAs in the LSA Request List. As LS Updates are received, LSAs in the LSA Request List. If an LSA has not been received, the LS Request packet will be re-transmitted.


As such, LS Acks are not used here but they are certainly used as part of the reliable flooding mechanism.


I would appreciate you rating the post if it helps.


Paresh

vladrac-ccna Wed, 04/26/2006 - 19:17
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Well, I guess I was wrong then,


I misinterpreted :


"Database synchronization. Database Description, Link State Request, Link State Update, and Link State Acknowledgement packets (described in a later section) are exchanged to ensure that both neighbors have identical information in their link-state databases"


from Jeff


ACKs are only used in exchange of update lsa, and for database acknowlegment, the slave acknowledges the packet by sending a DD packet with the same sequence number


Vlad


btw, how do you find time to be here all the time, Paresh! you're my netpro idol eheheh

pkhatri Wed, 04/26/2006 - 19:25
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No probs...


I only started being on NetPro once I embarked on getting my CCIE certification. Once I did get on, I found that this is addictive stuff (spoken like a true geek!) so here I am !!!


Paresh

mheusinger Thu, 04/27/2006 - 05:38
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Hi Paresh,


so how far are you in progressing towards CCIE? And how far are you with reading RFCs?

Anyhow, Mr. Purple, have fun and yet do not forget: There is life outside the forum as well!


:-)


Good Luck!


Hope this helps! Please rate all posts! LOL


Cheers, Martin

philth_123_2 Thu, 04/27/2006 - 03:13
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Thanks Paresh,

I hadn't reached section (10.10) at the time I posted.


I was referring to table 8 'OSPF Packet Types' in RFC2328 which states the following:


"OSPF's Hello protocol uses Hello packets to discover and maintain neighbor relationships.

The Database Description and Link State Request packets are used in the forming of adjacencies. OSPF's reliable update mechanism is implemented by

the Link State Update and Link State Acknowledgment packets."


This came across as a little confusing when comparing to Doyle, but I have since read 10.10 as you suggested and agree.


Thanks again.


Phil.


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