So in this series we're going to learn
from our multihoming examples that we
covered earlier on to have a look at
some particular BGP case studies. Several
of these case studies are based on
real-life examples that the network
startup Resource Centre team have worked
with various operators in different
parts of the world we're going to look
at several of these the first one we'll
have a look at is what's known as
peering priorities now when we're
covering the multihoming slides we
talked about setting local preferences
for different types of customers now as
network operators move from having a
single upstream to deploying BGP with
multiple external connections they need
to have a more formal process for how
these priorities are set up we need to
establish priorities for BGP customers
we need to establish priorities for
different peering partners because some
partners might be more significant than
some of the others and we need to
establish cost or benefits for
participating at different exchange
points because it's quite common for
suddenly the larger operators to
participate at more than one internet
exchange point we also need to establish
the cost or benefits for different
transit connections again for the same
reason some transit connections may cost
more have different latencies different
contention provided by upstream provider
and so forth so the typical
prioritization would be something like
this the most preferred would be BGP
customers because we would like traffic
from us and from the internet to go to
our BGP customers directly not via our
peers or our transits the next
preference would be our private peers we
want traffic from us to go to our
private peers over the direct cross
connect we won't want this to go over
say a local exchange point on the
regional exchange point or
even our paid transit because a private
PA connection is usually a direct fibre
cross connect that both we and our
private peer can control directly the
next preference would be the local
internet exchange point the local
internet exchange point has all our
local traffic all our local piers and we
prefer to keep local traffic as local as
possible it's quite likely that some of
our local peers would participate in
regional exchange points and of course
they'll be visible through our last
resort transit provider so we really do
want to keep our local traffic crossing
the local exchange point following that
we'd have the regional exchange point
this might be in another country what
might even be in another continent again
the idea is to try and keep regional
traffic regional and avoid having paired
traffic going over our transit
connection and the last resort or last
preference as is called in the slide the
last resort would be the paid transit
and this will cost money for the
physical connectivity and for the
traffic and no doubt will come at
significant latency I'm quite likely
with potential lack of bandwidth impact
as well the slide shows a typical set of
local preferences that an operator might
be using so for our BGP customer we
would set local craft to 50 our private
pier we would set local pref 200 the
local exchange point we probably set
local preference 70 the regional
exchange point we set local pref 140 of
course the default local preference is 100
and then we'd have a primary paid
transit provider maybe local pref 50
and a backup paid transit if we have a
second transit provider going down to
local pref 40. These values are just
examples if you look around at what
different operators do they all have
this structure in the local pref
settings but the various they use will
be entirely up to their own choice.
© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.
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