[LIP] Re: Re: IP module xmitting packets (Amit Kucheria)

From: Amit Kucheria <[email protected]>
Date: Tue, 13 Jan 2004 14:02:46 -0600 (CST)
To: linux-india-programmers-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
Subject: Re: [LIP] IP module xmitting packets
Message-Id: <Pine.LNX.4.44.0401131346380.11750-100000-VCzcDsiKySBFvdcdzOrui4dd74u8MsAO@public.gmane.org>


>
> On Tue, 13 Jan 2004, suresh kumar wrote:
> 
> > 
> > Hi, When the packets are being sent out from the linux system, ip
> > module first sees if there exists a routing cache entry and if not it
> > will see the fib creates an routing cache entry and xmits the packet
> > in the respective interface. So for each connection if it creates a
> > routing cache entry and if it first checks for the subsequent packets,
> > I think it is a bit costly than checking fib i.e. routing table. One
> > reason which I could find for TCP connections is, routing cache helps
> > in keeping track of the TCP state information and for all the other
> 
> As far as i can remember, the routing cache did not keep track of TCP 
> connection state (that is the job of the TCP state machine). The routing 
> cache is used for exactly what its name signifies: routing.
> 
> > protocols to know which ports are being in use which can be viewed by
> > netstat. (correct me if I am wrong). apart from the mentioned reasons,
> > is there ne other reason for it to maintain routing cache entry
> > especially in case of UDP.  cheers Suresh V.V Suresh Kumar
> 
> I dont think the routing cache cares about TCP/UDP. It simply indexes
> (hashes) the routes based on source, destination and TOS values. See 
> rt_hash_code().
As u said "routing cache is used for exactly what its name signifies: routing.", I don't find any reason of maintaining an entry for each connection in the routing cache, and xmitting packets based on the entries and not on the fib could be more costly as no. of entries in the fib will be much less than that of in routing cache. If u find any reason pls. post it. Either I am missing some thing critical or I got to dig in some more.

> 
> /Amit
> 
> -- 
> I'm an angel!!! Honest!
> The horns are just there to hold the halo up straight.
> -----------------------------------------------------
> Amit Kucheria             | amitk@ NOSPAM ittc.ku.edu
> Wireless Systems Engineer | 760-822-8529
> Metric Systems Corp.      | Vista, CA 92083
> -----------------------------------------------------
> 
> 


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