2006.06.05 NANOG-NOTES interdomain routng via Wiser, Ratul Mahjan

Tue Jun 6 09:57:08 UTC 2006

2006.06.05
A simple coordination mechasims for interdomain routing
[slides are at:
http://www.nanog.org/mtg-0606/pdf/ratul-mahajan.pdf

Ratul Mahjan
David Wetherall
Tom Anderson
University of Washington now @ Microsoft Research

the nature of internet routing
within a contractual framework, ISPs select routes
 that are best for themselves.
Potential downsides
 higher BW provisioning
 requires manual tweaking to fix egregious problems
 inefficient end-to-end paths

An alternative approach: coordinated routing
ISPs have joint control
 path selection is based on the preferences of both ISPs
Potential benefits
 lower BW provisioning
 no egregious cases that need manual tweaking
 efficient end-to-end paths
  basis for interdomain QoS

Existing mechanisms cannot implement coordinated routing
route optimization boxes help (stub) ISPs pick better
 routs from those available
MEDS implement receiver's preferences.
Cannot create better paths that don't already show up
 in the routing table.

What makes for a good coordination mechanism?
MEDS have some nice properties
 ISPs can express their own metrics
 ISPs are not required to disclose sensitive info
 lightweight
 requires only pairwise contracts
Provides joint control and benefits all ISPs.

Our solution: Wiser
operates in a lowest-cost routing framework
 downstream ISPs advertise their cost
 upstream ISPs select paths based on both their
  own and received costs.

Problems with vanilla lowest-cost routing
ISP costs are incomparable
Can be easily gamed

When you bring incomparable costs together, the ISPs
that use higher costs win out.

Cost normalization
Normalize costs such that both ISPs have "equal say"
Normalize such that sum of costs is the same.
Makes the system harder to game.

Bounds on cost usage
Downstreams log cost usage of the upstream ISPs
Compute the ratio of avg. cost of paths used and
announced
Contractually stipulate a bound on the ratio.
Similar to existing ratio requirements.

Wiser in action
Announce costs in routing messages.
normalization occurs between ISP pairs.

Example results
using major ISP topologies for experiments
Wiser provides better control under link failure.
Wiser produces shorter path lengths

Implementation
XORP prototype
Simple, backward-compatible extensions to BGP
 embed costs in non-transitive BGP communities
 border routers jointly compute normalization
 factors and log cost usage
 a slightly modified BGP decision process
Benefits even the first two ISPs that deploy it.

Summary
Wiser is a simple mechanism to coordinate
 interdomain routing
 may lower provisioning, reduce manual tweaking,
 produce more efficient paths and help with interdomain
  QoS
Feedback: ratul at cs.washington.edu
http://www.cs.washington.edu/research/networking/negotiation/

Danny McPhereson:
Q: how do you normalize across multiple ISPs?
A: routing advertisements happen on the sum of the
costs announced from me to you, and from you to
me.  He derived it from different values in
his experimentation; utilization and latency
in general.

Q: Randy Bush: Whatever metrics are, you just normalize
by summing them up.  But Danny notes if you have
multiple ISPs, how do you normalize them together?

Q: Danny: where was the 20ms of control plane savings
seen that he claimed in slide 11?
A: That was based on default ISP policy, prefer customers
over peers, etc.
So the delay was control plane plus data plane; it
wasn't control plane alone.
He based it on the old rockefuel equation.

Randy Bush: vendors--this is cool stuff, open your
ears.

Break time now.