register.com down sev0?

Tony Li tony.li at tony.li
Fri Oct 27 15:45:48 UTC 2006


Hi Vadim!

Vadim Antonov wrote:
> On Thu, 26 Oct 2006, Tony Li wrote:
> 
>> Further, uRPF is frequently a very inefficient means of implementing BCP
>> 38.  Consider that you're going to either compare the source address
>> against a table of 200,000 routes...
> 
> That would be, well, about 6 memory reads.
> 
> Radix trees are great.


They are indeed.  If a radix trie is indeed used, you would expect to
see about log2(200,000) + 1 = 19 reads on average.

>> or against a handful of prefixes that
>> you've statically configured in an ACL.
> 
> Which will take much longer with line-by-line sequential matching.

Fortunately, modern ACL implementations frequently use TCAMs (1 read) or
tree based structures (log2(handful) + 1) as well.

As always, the details of a particular implementation are everything.  YMMV.

Tony




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