>good explanation but still can you be a bit more
>layman ?
To be quite honest, no, not within an email message. Generating BGP
routes can foul up not just one's own network, but the Internet as a
whole. It is not a simple subject.
At CertificationZone, I wrote a 3-part tutorial, perhaps 100 pages or
so, about BGP policy--and that was an introduction. When I've done
internal Nortel seminars for research-level developers, I can spend
hours to days discussing scenarios for using communities, the
differing roles of communities and route selection affectors such as
MED and local pref, the interactions of communities with MED and
local pref, etc.
Recently, after a failed test of a US missile defense system, the
official who gave the press briefing observed, "this _is_ rocket
science." In the case of Internet routing, I began to get the idea
of what actually was happening when I read the RIPE-181 document
(also as an RFC) and thought about it long and hard. The RPSL RFCs,
especially "Using RPSL in Practice," help. Following the NANOG and
RIPE Routing WG mailing lists helps a great deal.
>
>
>suaveguru
>--- "Howard C. Berkowitz" <[EMAIL PROTECTED]> wrote:
>> >suaveguru wrote:
>> >>
>> >> knows anything below what it does ?
>> >>
>> >> route-map MikeTest permit 10
>> >> set community 6461:701 additive
>> >
>> >Adds community 6461:701 to the list of communities
>> >carried with the route. Without keyword 'additive',
>> >it will remove other communities.
>> >
>> >It is used with BGP.
>> >
>> >Sa–a
>>
>>
>> Excellent explanation of what the command itself
>> does. One of the
>> hard things in learning real world "BGP" is that the
>> Border Gateway
>> Protocol (BGP) is a small part of the complexity of
>> global internet
>> routing.
>>
>> In this example, the meaning of community 6461:701
>> is defined by AS
>> 6461 (the part before the :). While this community
>> will be used to
>> make some sort of policy decision, the actual
>> policy, contrary to
>> many discussions, is NOT carried by BGP. For
>> example, community 701
>> of AS 6461 might mean that an AS _should_ treat
>> routes with this
>> community as high precedence. A receiving AS is not
>> obligated to do
>> so, and, unless there are prior agreements with AS
>> 6461, may not even
>> know that is the intended meaning.
>>
>> To take a different example, let's say AS 6461 is an
>> academic
>> research network manager. Other universities
>> belonging to the same
>> network will recognize community 701 routes as
>> belonging to the
>> research network. Indeed, if another university were
>> AS 6060, it
>> still might originate routes with origin AS 6060 but
>> community
>> 6461:701, because all the participants know that
>> 6461:701 denotes
>> membership in the cooperative network.
>>
>> The meaning of communities MAY be available from
>> routing registries,
>> but may simply be a private admininistrative
>> agreement between AS.
>>
>> The key things to remember:
>>
>> Policies are implemented in filters/route list
>> match/set, etc.
>> statements that are not transmitted by BGP
>>
>> Information to make policy decisions is
>> transmitted by BGP.
>>
>> _________________________________
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>
>
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