Subject: Re: nat configuration
To: Bill Studenmund <>
From: Andrew Brown <>
List: tech-net
Date: 01/09/2001 13:33:32
>Cleaning out old mail...'s not spring yet.  :)

>> will almost do what i want.  when i translate the /8 to my /24, and
>> to (to match my ppp link), i get connectivity
>> for all my machines, but only one of them can have an active ping (to
>> the outside world) running at any given time.
>> is there a way to do this?  the userspace ppp implementation in pkgsrc
>> can do this, but i'd rather use a kernel space ppp implementation.
>Are you sure the userspace ppp implimentation can do that?

yep.  i was sort of speaking from past experience, but just to be sure
i verified it again.

   # uname -srm
   NetBSD 1.5K i386
   # pkg_info -I userppp
   userppp-001107      User-PPP package as found in FreeBSD and OpenBSD

and i can get at two (probably more, but two is more than one to
define my point) machines behind the nat pinging the same outside
address (to demonstrate proper muxing/demuxing of the pings).

>I use NAT over my DSL, and only one of the boxes inside my net can ping
>out at the same time. It's not a ppp issue, and I'd be surprised if using
>a different ppp made it work. :-)

it's a nat issue, not a ppp issue.

>The problem is that NAT doesn't support it.

yes, i know.  that's the point.  ipnat, that is.  hmm...i wonder what
ill effects i'd get from using the userspace ppp with aliasing (ie,
nat) turned on as well as ipnat...

>Hmmm.... I just tried it, and now it works! I thought it didn't used to.
>Either I misremembered, or it's been fixed.

um...what works?  a more current nat can mux pings?

>All my machines are running 1.5.

all my machines are running current with less than a two month lag
behind today.

>If it really works with userland ppp (which I thought was a downgrade from
>1.5's ppp) but not kernel ppp, then there's a ppp bug.

the userspace ppp is, afaik, a *completely* separate and distinct
implementation of ppp.  all it requires of the kernel is a serial
interface (with a modem) and a tunnel interface (for packets to go
through).  it's not a downgrade...perhaps a "sidegrade".

the nat (called aliasing) in the userspace ppp is what actually
handles the multiple outbound pings.  i imagine it's fiddling with the
icmp echo request identifier and using it as it uses the local port
number rewriting for udp and tcp.

|-----< "CODE WARRIOR" >-----|             * "ah!  i see you have the internet (Andrew Brown)                that goes *ping*!"       * "information is power -- share the wealth."