North American Network Operators Group

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Can P2P applications learn to play fair on networks?

  • From: Sean Donelan
  • Date: Sun Oct 21 03:42:11 2007

Much of the same content is available through NNTP, HTTP and P2P. The content part gets a lot of attention and outrage, but network engineers seem to be responding to something else.

If its not the content, why are network engineers at many university networks, enterprise networks, public networks concerned about the impact particular P2P protocols have on network operations? If it was just a
single network, maybe they are evil. But when many different networks
all start responding, then maybe something else is the problem.

The traditional assumption is that all end hosts and applications cooperate and fairly share network resources. NNTP is usually considered a very well-behaved network protocol. Big bandwidth, but sharing network resources. HTTP is a little less behaved, but still roughly seems to share network resources equally with other users. P2P applications seem
to be extremely disruptive to other users of shared networks, and causes
problems for other "polite" network applications.

While it may seem trivial from an academic perspective to do some things,
for network engineers the tools are much more limited.

User/programmer/etc education doesn't seem to work well. Unless the network enforces a behavor, the rules are often ignored. End users generally can't change how their applications work today even if they wanted too.

Putting something in-line across a national/international backbone is extremely difficult. Besides network engineers don't like additional
in-line devices, no matter how much the sales people claim its fail-safe.

Sampling is easier than monitoring a full network feed. Using netflow sampling or even a SPAN port sampling is good enough to detect major issues. For the same reason, asymetric sampling is easier than requiring symetric (or synchronized) sampling. But it also means there will be
a limit on the information available to make good and bad decisions.

Out-of-band detection limits what controls network engineers can implement on the traffic. USENET has a long history of generating third-party cancel messages. IPS systems and even "passive" taps have long used third-party
packets to respond to traffic. DNS servers been used to re-direct subscribers to walled gardens. If applications responded to ICMP Source Quench or other administrative network messages that may be better; but they don't.