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Re: Fwd: Alternative to NetFlow for Measuring Traffic flows
- From: William B. Norton
- Date: Wed Dec 18 02:12:50 2002
At 04:36 AM 12/18/2002 +0000, Sean M.Doran wrote:
Agreed there is an incremental operational cost of peering.
I have found peering to have additive value; a lot of 1-2 Mbps peering
sessions can save as much money for you as a single large traffic peer.
The more traffic, the stronger the case for peering.
Sadly, this completely ignores the cost of implementing and maintaining
peerings. BGP does not exactly configure itself, and current routing
technology is somewhat frail -- if it breaks, somebody has to pick up the
pieces; if suboptimal routing results from a peering, somebody will have
to go and tweak things.
Since the Internet is not exactly static, these things creep up from time
to time even after a peering is established.
I've heard differing views on the importance of peering. One view is that
Peering is a "Local Routing Optimization" for which an ISP always has the
fallback of transit. Others view the peering session as very important to
both peers for capacity, cost and performance reasons. These two different
views tend to lead to different levels of resources and overhead. Most
peers minimally expect (or require in BLPAs) each other to have a 24/7 NOC
that works diligently to fix a broken peering session. Generally, this is a
(financially) small incremental expense since the NOC staff and facilities
etc. are already in place.
An exhaustive itemization of the costs of any given peering is a of vital
component of a cost-benefit analysis, particularly where much of the
benefit is a reduction in monthly usage based billing costs, or a deferral
of an upgrade of a flat rate contract, rather than installing new parallel
connectivity to meet the demands of traffic growth. While such a list
will vary from organization to organization, and some organizations may be
tricky to complete, one can consider the primitive case of a transition
from being singly homed to a transit provider to bring up an initial peering.
Here again I agree, all things considered equal, fewer sessions cost less
to build and manage than more sessions. Thankfully, peering sessions
generally tend to stay up, providing the benefits of peering 99.9..% of the
time. I haven't heard many Tier-2 ISP Peering Coordinators (yet) complain
that the ongoing operational overhead of their peering sessions was overly
burdensome compared to the benefit they derive from their peering sessions.
I have heard a few of the Tier-1 ISPs make these complaints however... but
this may lead to a different conversation.
Among the things to be considered: PA address space, BGP (and making sure
that the routers can handle the load, and so can the people operating
them), avoidance of accidental transit, what happens to the peering
traffic when the peering fails from time to time (or fills up with growth
traffic over time), NOC-to-NOC coordination, impact on actual and
potential SLA offerings, and so on. The immediately subsequent
peering may not make much of an impact on many of these however there are
real incremental costs. Some of these may not rise linearly in proportion
to the number of peers (e.g. there may be a step change),
but rather may be a function of that number, the number of your routers
which talk eBGP, and your overall traffic load.
I know a handful of cases where a broad peering strategy had a fairly
clear negative impact on the bottom line even though the saving in transit
fees was both directly measurable and large. Anecdotes are not general
proofs, but do underline the uncertainty in your statement: "a lot of ...
peering sessions CAN save as much money ... as a single large traffic
peer". [emphasis mine]
Tough to measure and quantify these incremental costs whereas the
improvement in performance and cost savings are relatively easily measured
and calculated. I seem to remember reading a paper about that...
Unfortunately, discussions here seem to focus mostly on measuring the
reduction in transit fees. Wouldn't it be nice if this could be coupled
with reasonable discussion about the increase in other costs, and how for
some networks these costs are much higher than for others?