From: Howard C. Berkowitz (hcb@gettcomm.com)
Date: Thu Jul 08 2004 - 18:06:29 GMT-3
At 9:48 PM +0100 7/8/04, Pierre-Alex Guanel wrote:
>Hi Howard,
>
>This is the basic idea I had in mind.
>
>It looks like if I wanted to know the details I would need to spend the time
>reading the RFC
>
>and doing it step by step. Could be of good use for academics but for the
>lab, I am not quite sure.
>
>Thanks for your input.
It's probably not relevant for the lab, as long as you remember the
only control is at the interface cost level. The current RFC for
OSPF, incidentally, is 2328.
>
>Pierre
>----- Original Message -----
>From: "Howard C. Berkowitz" <hcb@gettcomm.com>
>To: "Ccielab@Groupstudy.Com" <ccielab@groupstudy.com>
>Sent: Wednesday, July 07, 2004 7:38 PM
>Subject: Re: Advanced: OSPF Algorithm
>
>
>> At 7:23 PM +0100 7/7/04, Pierre-Alex Guanel wrote:
>> >How does OSPF add the cost of the links?
>> >
>> >>From what I have seen, it does not seem like the cost in the packet gets
>> >updated from hop to hope.
>> >
>> >The process of flooding just passes the original lsa along, unaltered.
>> >
>> >>From what I read, the OSPF algorithm knows how to find all the costs
>and add
>> >them up from the LSA using the Djakstra algorithm.
>> >
>> >Yes I know its all explained in RFC 2178 ...section 16, but I am
>looking at
>> >a simple explaination.
>> >
>> >thanks,
>> >
>> >Pierre
>>
>> Let's keep this at the intra-area case at the moment, which is all
>> the Dijkstra algorithm cares about. Link state protocols do not
>> transmit routes, but router links (and a list of subnets connected to
>> them) and network/subnet links (with a list of router interfaces
>> connected to them).
>>
>> The Dijkstra algorithm builds a tree, matching up the
>> networks-with-routers and the routers-with-networks. Each time it
>> steps closer to a destination, it picks the lowest interface cost at
>> that hop. When the final best paths are selected, OSPF adds up the
>> costs along the path, and then sends the route to the routing table
>> installation process. The intra-area routes are never passed to other
>> routers during flooding. Route metrics are computed independently by
>> each router, from its own position in the topology.
>>
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