Date: Sat, 29 Jun 2002 05:34:30 -0700 From: Luigi Rizzo <rizzo@icir.org> To: net@freebsd.org Subject: ipflow_has ? Message-ID: <20020629053430.A70505@iguana.icir.org>
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Hi,
looking at the code in ip_flow.c, i notice that the hash
function ipflow_hash() uses both the source and destination
address as parameters, and additionally, it never considers
the lower two bits of the destination addres. The code is below,
IPFLOW_HASHBITS is 6:
unsigned hash = tos;
int idx;
for (idx = 0; idx < 32; idx += IPFLOW_HASHBITS)
hash += (dst.s_addr >> (32 - idx)) + (src.s_addr >> idx);
return hash & (IPFLOW_HASHSIZE-1);
Of course it is just an optimization, but shouldn't routing
decisions be based on the dst address only ?
Just using the dst address would slightly simplify the function,
and especially has the potential of collapsing a lot of information
in the ipflow cache -- consider the case of a router box in front
of a busy web server.
Comments ?
cheers
luigi
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