North American Network Operators Group

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Scalability issues in the Internet routing system

  • From: Andre Oppermann
  • Date: Tue Oct 18 11:37:49 2005

I guess it's time to have a look at the actual scalability issues we
face in the Internet routing system.  Maybe the area of action becomes
a bit more clear with such an assessment.

In the current Internet routing system we face two distinctive scalability

1. The number of prefixes*paths in the routing table and interdomain
   routing system (BGP)

This problem scales with the number of prefixes and available paths
to a particlar router/network in addition to constant churn in the
reachablility state.  The required capacity for a routers control
plane is:

 capacity = prefix * path * churnfactor / second

I think it is safe, even with projected AS and IP uptake, to assume
Moore's law can cope with this.

2. The number of longest match prefixes in the forwarding table

This problem scales with the number of prefixes and the number of
packets per second the router has to process under full or expected
load.  The required capacity for a routers forwarding plane is:

 capacity = prefixes * packets / second

This one is much harder to cope with as the number of prefixes and
the link speeds are rising.  Thus the problem is multiplicative to

Here I think Moore's law doesn't cope with the increase in projected
growth in longest prefix match prefixes and link speed.  Doing longest
prefix matches in hardware is relatively complex.  Even more so for
the additional bits in IPv6.  Doing perfect matches in hardware is
much easier though...