Re: A new spin on multihoming: multihoming classes.

[Michael Richardson <mcr@sandelman.ottawa.on.ca>]

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>>>>> "Peter" == Peter Tattam <peter@jazz-1.trumpet.com.au> writes:
    Peter> On Fri, 7 Sep 2001, Geoff Huston wrote:
    >> But as to the assertion that 8,192 is some magical preferred number of 
    >> 'root prefixes', then I'm not sure that I can agree.

    Peter> I am concerned that the whole multihoming issue hinges on the
    Peter> answer to whether 
    Peter> BGP can be made to work with larger DFZ than we anticipated.

    Peter> I'm not sure where 8K comes from.  8K = 2^13. 

    Peter> Maybe it relates to the size of a practical switching table in very fast
    Peter> routers built using ASICs. 

  No.
  Currently shipping OC-48 capable ASICs do 100K+ easily (for IPv4). 
  Announced OC-192 ASICs do the same or more, and most designs have roadmaps
to OC-768, assuming that the OIF/NPF people finish defining appropriate
electrical interfaces to get packets between ASICs at that rate :-)
 
  Some solutions scale as the number of bits that matter. I.e. a single /128
entry simply takes twice as much space as two /64s, while other solutions
must store as many bits as the worst case length. The pathological situation
(highest price, highest power dissipation) is ternary CAMs which seem to do
72 bits or 144 bits only as options. 

  I too would like to know about this 8K DFZ.
  I can see that there are BGP convergence reasons why one might want to
attempt to keep the size small, but this number scares me.

    Peter> In my opinion some of the measures that prevent route flapping may actually
    Peter> cause more damage than good because they introduce stepping functions into the
    Peter> differential equation that would model the DFZ.  They work now because the
    Peter> paramters have been determined empirically - I'm uncertain that
    Peter> they will scale 
    Peter> indefinitely.

  That's an interesting observation.
  
]       ON HUMILITY: to err is human. To moo, bovine.           |  firewalls  [
]   Michael Richardson, Sandelman Software Works, Ottawa, ON    |net architect[
] mcr@sandelman.ottawa.on.ca http://www.sandelman.ottawa.on.ca/ |device driver[
] panic("Just another NetBSD/notebook using, kernel hacking, security guy");  [
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