Date: Mon, 01 Jul 2002 13:31:56 +0200 From: Andre Oppermann <oppermann@pipeline.ch> To: Luigi Rizzo <rizzo@icir.org> Cc: net@freebsd.org Subject: Re: ipflow_has ? Message-ID: <3D203DAC.B32AF1A8@pipeline.ch> References: <20020629053430.A70505@iguana.icir.org>
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Luigi Rizzo wrote: > > 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 ? Routing decisions yes. But ipflow is about flows. And flows are from one IP to another. This is why both is being hashed. > 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. If you change that please rename it to route_cache or so but no it shouldn't be called ipflow anymore then. This caching only helps in an Intranet where you have only a handful of routes. If you do Internet routing with many destinations or you have a full view then it'll make the routing slower because it is busting/cycling the cache all the time. -- Andre To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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