[Idr] On FIB sizing...

[Tony Li <[e-mail]>]

On Dec 15, 2012, at 4:26 PM, Jeff Wheeler <[e-mail]> wrote:

> I thought 2^128 for IPv6 was stupid.  It was an expensive choice,
> given the challenges which still exist in dealing with 128 bit
> arithmetic in many environments, FIB consumption, legibility of
> addresses, and so on.  


As an aside, FIB sizing only varies loosely with the maximum number of bits in the address because the FIB can be constructed to hold only prefixes.  Thus, what's more important is the average and distribution of prefix lengths.

Thus, (for a core router) the choice of /128 is largely irrelevant when remote prefixes are all /64 and shorter.  For a datacenter switch that has to store possibly many /128's, this is more of an issue, but is offset because there is no ARP cache to deal with.

Tony