>At 10:19 AM 2/15/01, Robert Nickson wrote:
>>sorry for OSPF
>
>You should have left out that extra piece of information that the packets
>you mention are for OSPF, and anyone who didn't know that should go back to
>studying. &;-) This is an odd way of saying that you would have to know at
>least that much for the routing exam. You don't have to know the exact
>frame formats. It's must more important to understand the general
>principles of how OSPF routers become adjacent and synchronize their
>databases, and to be able to recognize the commonality in the frame formats.
I'll have a "metapaper" about link state routing protocols appearing
shortly at CertZone (I think March 1), which identifies the general
principles that apply to both OSPF and ISIS. There will be a series
of more detailed papers following, on both single area and
hierarchical OSPF and ISIS.
>
>With regards to frame formats, I think you should know the following:
>
>OSPF runs directly above IP, using protocol type 89. (It does not use TCP
>or UDP.)
>
>OSPF packets have an IP TTL of 1.
>
>OSPF packets are sent to a reserved multicast address, either AllSPFRouters
>(224.0.0.5) or AllDRouters (224.0.0.6).
>
>Each OSPF packet type begins with an OSPF packet header.
5 packet types, all but hello carrying one or more Link State
Advertisements (LSA). One thing that can really be confusing is that
one of the packet types is Link State Acknowledgement. This packet
is usually abbreviated LSAck to avoid conflict with LSA. A LSAck can
carry one or more LSA headers (LSA's have both fixed-length headers
and variable-length specific information).
>
>The Hello packet is used to find neighbors and detect problems.
>
>All the other packet types carry link-state advertisement information of
>some sort.
There are about a dozen LSA types. Some (e.g., type 6 and type 8)
are not used by Cisco. Others (type 9 and above) are still
experimental or used in new technologies such as OSPF traffic
engineering. For general consumption, know about 1-5 and 7.
>
>The best book for describing what you should "really care about" when
>learning OSPF is Howard Berkowitz's "Designing Routing and Switching
>Architectures." I think he does a better job than Doyle in making sure the
>reader focuses on what really matters. And, as we know, he dispels urban
>myths with style and aplomb.
>
>Priscilla
I can't help but giggle a bit here. I was the reviewer for Jeff's
OSPF chapter, and he reviewed some of my CertZone BGP papers. We
hold each other in high respect, I believe, but we have different
writing styles. Jeff, for example, feels that it's valuable to quote
a lot of RFC-ish material at the start of a chapter, to establish
precision for the discussion in the latter part of the chapter. It's
probably fair to say that his mental model is more
bottom-up/synthetic than mine, which is more top-down/analytic.
As far as urban myth dispelling, I can't help but wonder if aplombing
is one of the characteristics of a roto-router. Apologies to those
outside North America for the regional reference.
When I wrote the Designing Routing and Switching Book, I was
concentrating neither on configuration and troubleshooting (more
Jeff's focus) nor why various alternative choices were made in the
protocol itself (see John Moy's and Radia Perlman's books). I may be
submitting some proposed extensions to OSPF to the IETF, but then I
will be wearing my protocol architect hat, which is different from my
network architect hat.
>
>
>
>>-----Original Message-----
>>From: Robert Nickson
>>Sent: Thursday, February 15, 2001 10:10 AM
>>To: [EMAIL PROTECTED]
>>Subject: ccnp routing frames
>>
>>
>>On the CCNP routing exam is there any questions on (i.e do i have to
>>memorise)
>>frame for frame the format of hello packets,DD packets,LSA packet
>>frames...etc
>>like ..version,type,packet length,route ID,Area ID,Checksum,Au
>>type,Authentication etc etc
>>or is there certain fields i should learn
>>
>>Any help would be useful
>
>
>________________________
>
>Priscilla Oppenheimer
>http://www.priscilla.com
>
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