Global BGP community values?

I think everyone at one point or another has tried to influence incoming
data flows via BGP. About the only tool available to influence the BGP
decisions in far away places is via AS-PATH length. This turns out to be
a fairly never-ending iterative process - that at best achieves 80% of its
intention. It also doesn't allow for accurate decision making. As an
alternative, neighboring ISPs and their customers usually design some BGP
community system which is then used to influence the BGP decision process.

Why can't this be extended globally [if this has already been done and
written up in some BCP RFC - just point it out to me]? What if we all
agreed that if some community value of say 1000000-2000000 [example] is
seen, then those community values are to take precedence above all other
metrics. 1000001 could mean - "this is the best path for me - always send
pkts this way no matter what the other metrics might say". We could build
up a table of these global community strings. ISPs that don't use it - no
harm done. But the more ISPs (tier 1 & 2) that do use it - the better the
end customer and ISPs have on influencing data flow.

Comments welcome.

Hank Nussbacher

Btw, a VERY GOOD idea (through I do not know if it should have success,
but it don't need extra money etc). You are right - the only 2 ways to
control incoming traffics are:
- AS-PATHS length
- communities declared by the ISP which allow to decrease localpref (or
increase it).

But the second way of the control (just as the first one) don't work
globally, because every ISP have it's own communities (or have not any),
and moreover, to separate primary and back-up pathes, you need to decrease
localpref by all route paths; this means you should predict all possible
pathes where primary and back-upped pathes can collide (the points of the
paths selection before back-up became active and after it became
inactive), and so on.

There is just now a few standard communities - such as _NO-EXPORT_. It is
good idea to standartisy a few other _RECOMMENDED_ _GLOBAL_ communities.

On the other hand, it's often when you need not GLOBAL but REGIONAL (such
as _AMERICA only_ or _Europe ONLY_ communities. But anyway, any
recommendations allowing to standartisy communities and use some global
control values will be appreciated by the ISP and the customers over the

Btw, I think it's much more usefull than to pay a lot of money for useless
MLPS (next one Another Terrible Mistake) developments... /but it's just my
personal opinion/.

Alex Roudnev, the head of NOC, Relcom, Moscow, Russia.

PS. It's standard this day to use new community notation, such as 2118:10.
And it's almost standard to use AS_NUMBER:EXTENTION communities as the
local communities. This means you should declare GLOBAL values as 0:1 or
0:10 or so on - with some unexisting AS_NUMBER before the extention.


whois -h AS2118
whois -h AS702

and so on... this data objects contain an examples.