Here is what I think about the wording below. They key thing to remember is that a
withdrawn message does not need to carry as much information about a routes attributes
as does an advertisement message. In both cases, a route describes a destination and
a BGP Next_Hop address along with other attributes including as paths/communities/
etc. In the first case, the advertisement, single routes are noted with their full
information provided such that the receiving peer can properly evaluate the route.
However, for a withdrawn route, the receiver really only needs to know that the route
is unreachable and thus, only the smallest piece of information which uniquely
identifies the route, that being the destination prefix, is transmitted. Because
withdraw advertisements transmit so little information about the route, and because
what they do transmit is rather important for route stability, they are bundled
together when transmitted.
Does that clarify things a bit?
Pete
*********** REPLY SEPARATOR ***********
On 1/10/2001 at 8:32 PM Jaeheon Yoo wrote:
>Hi, all
>
>Now I'm reviewing BGP 4 for the upcoming BSCN test. I'm getting
>nervous about it.
>
>In p.17 of RFC1771, what does "one route" mean? What's the difference
>between one route and one destination? Or should "route" be replaced
>with "path" as is used in BSCN book?
>
> An UPDATE message can advertise at most one route, which may be
> described by several path attributes. All path attributes contained
> in a given UPDATE messages apply to the destinations carried in the
> Network Layer Reachability Information field of the UPDATE message
>But in the next paragraph, "route" is used as "destination".
>
> An UPDATE message can list multiple routes to be withdrawn from
> service. Each such route is identified by its destination
>(expressed
> as an IP prefix), which unambiguously identifies the route in the
> context of the BGP speaker - BGP speaker connection to which it has
> been previously been advertised.
>
>I hope somebody out there will clarify this to me.
>Thanks in advance.
>
>Jaeheon
>
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