thank you for so rapid answer.
i still can't understand . in the host  when we add a tap device, uml set
after that we can reach ? we don't need to add route .  is that i  understand this as  if we add a tap device , just think that tap device is a vitural 
network interface of the host ?? i have taken a tumble.

2006/6/19, Stefano Melchior <>:
On Mon, Jun 19, 2006 at 02:58:14PM +0800, paul john wrote:
Dear paul john,
> i just wondering about the network setup .  as i know , if the host act as a
> gate way it also should has an internal IP  so it can ping the umls .
> if use a bridge ,  the bridge should be set of the external ip , and the
> umls will be setup the internal ip , and umls will use tapN,
> but now in the host  if ping umls  obversily can't reach it (is that right
> just add a route to the host , umls can be reached ?
> like that , tap0 address is,  uml1 address is , and
> in uml1 set network as  ip gateway is
> and add route in host like that   addroute tap0 [this command
> maybe wrong , you just know the meaning]
> is that right ?

pratical example of conf:
iface tap0 inet static
pre-up tunctl -u <your-user>
pre-up bash -c 'echo 1 > /proc/sys/net/ipv4/ip_forward'
pre-up iptables -t nat -A POSTROUTING -o <your-internal-interface> -j MASQUERADE
post-down tunctl -d <your-user>

auto eth0
iface eth0 inet static
up route add -net dev eth0
up route add -net gw <your-public-IP>
> ).   i just don't understant  how tap works . so if you give me a practical
> setup ,will be very appreciated.

tap is a p-t-p connection between host and uml.
> also "exec linux ubd0=... umid=mytest eth0=..." , if edit the .bash_profile
> like that ,  it means the user can't login the host  ? as he login the host
> ,will be redirect to uml ?

yes, it is automatically "redirect" to uml image that is launched after
the login on host: I mean that you execute the login on host, then once
authenticated the first thing the the system does is to launch the uml
image (with that command). Then you will be on the uml.

> my understood is that , if the user login just start a uml instance for him
> . but if the uml instance is already there , how should i do ?

it was only an alternative way to reach it. You can somehow get the
/dev/pts/X serial connection on uml and then connect on the previously
launched uml by using screen or minicom.
this i still can't understand . if i already setup umls , and i want they login to redirct to the umls (assume the uml is,
"exec linux ubd0=... umid=mytest eth0=..." ,this cann't do that ,
may add a command in the users .bash_profile that ,ssh when he login ,the first command is loging in the uml

> thank you for your help .

Stefano Melchior, GPG key = D52DF829 - <>    --
Skype ID "stefanomelchior"

Version: GnuPG v1.4.3 (GNU/Linux)