Subject: Re: ip_flow.c
To: Charles M. Hannum <>
From: Jason Thorpe <>
List: tech-net
Date: 01/26/1999 23:37:13
On Tue, 26 Jan 1999 21:23:31 -0500 (EST) 
 "Charles M. Hannum" <> wrote:

 > 1) There's no need to check both ipforwarding and ipflow_inuse.

True 'nuff.  If ipforwarding == 0, there won't be any ipflows.

 > 2) There's no need to check the header checksum.  In the rare case
 >    where it's incorrect, either: a) we will fail to find a flow and go
 >    through the slow path anyway, or b) it will be dropped by the
 >    destination host.  I believe many hardware routers don't do this
 >    either.

Probably worth checking Router Requirements...

 > 3) There's no need to check the IP packet length.  Again, in the rare
 >    case where it's incorrect, it will be rejected on the destination
 >    host.  Furthermore, truncating the packet may actually reduce
 >    efficiency (e.g. by forcing us to repad a packet to send it out an
 >    Ethernet interface).

If you're referring to the change made in rev 1.6, this actually fixed
a bug which I believe caused some systems to crash... Bill Sommerfeld
can probably shed more light on this.

        -- Jason R. Thorpe <>