Actually, there isn't much hacking to be done at all.  
If you don't want ipforwarding, but want the extra mbufs, use:
options "NMBCLUSTERS=1024"
in your kernel config file.  If you're really paranoid, use 2048.
Otherwise, use options GATEWAY as well as the above parameter.

-Brian
On Jan 18, 11:29pm, "Neil J. McRae" wrote:
} Subject: Re: mb_map full
} 
} 
} > 
} > 	Hi,
} > 
} > I got a kernel message "Jan  9 09:39:47 colwyn /netbsd: mb_map full"
} > this morning. What does it mean? I never saw it before.
} > 
} It means that the kernel ran out of mbufs. Which to put simply are network
} buffers. It may help to build a kernel with options GATEWAY defined. If not
} then you have some, difficult, tweaking to do.
} 
} Regards,
} Neil.
} 
} 
} --
} --  neil@domino.org                     Domino: In the glow of the night.  --
} --  Free your computer and your <a href="http://www.NetBSD.ORG/">mind</a>  --
} ----------------  NetBSD: The best things in life are FREE!  ----------------
>-- End of excerpt from "Neil J. McRae"