Configuration help

I'm trying to use poptop to access a virtual machine and was hoping
somebody could help me understand what I need to do.

My virtual machine is running on linux in a proprietary engine thats
beyond my control.  The IP it uses to talk to the outside world is a
private 172.16 address, but I can specify that it either bind to a
physical interface or bridge to a TAP.  I prefer the TAP because it
keeps the low bandwidth VM traffic off my high bandwidth NIC.  I
installed poptop on CentOS 5 with yum, configured my Windows 7 box to
connect to it, and that seems to work.  At least it authenticates and
I can see traffic from my client to the server on Wireshark.

When I try to ssh from the client side into any 172.16.xxx.xxx, I see
the packets on the server side on interface ppp0.  When I try sending
packets from the server to the client, using the address that pptpd
gave it, I get nothing.  Debugging is compounding because I don't see
the VPN interface in Wireshark on Windows.  Only Linux.  So, I
installed a web server on the windows side, and tried viewing it from
the Linux side.  But nothing.  It appears traffic only goes 1 way:
client to the server.

Why can't the server send data to the client?


ifconfig output:

eth0      Link encap:Ethernet  HWaddr xx:xx:xx:xx:xx:xx
          inet addr:xxx.xxx.xxx.xxx  Bcast:xxx.xxx.xxx.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1504748 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2205475 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:283177506 (270.0 MiB)  TX bytes:2156819895 (2.0 GiB)
          Interrupt:233 Memory:ea000000-ea012800

ppp0      Link encap:Point-to-Point Protocol
          inet addr:172.16.0.81  P-t-P:172.16.168.1  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1396  Metric:1
          RX packets:30 errors:0 dropped:0 overruns:0 frame:0
          TX packets:129 errors:0 dropped:20 overruns:0 carrier:0
          collisions:0 txqueuelen:3
          RX bytes:1964 (1.9 KiB)  TX bytes:9300 (9.0 KiB)


route output:
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
172.16.168.1    *               255.255.255.255 UH    0      0        0 ppp0
xxx.xxx.xxx.0    *               255.255.255.0 U    0      0        0 eth0


/etc/pptpd.conf

###############################################################################
# $Id: pptpd.conf,v 1.10 2006/09/04 23:30:57 quozl Exp $
#
# Sample Poptop configuration file /etc/pptpd.conf
#
# Changes are effective when pptpd is restarted.
###############################################################################

# TAG: ppp
#	Path to the pppd program, default '/usr/sbin/pppd' on Linux
#
#ppp /usr/sbin/pppd

# TAG: option
#	Specifies the location of the PPP options file.
#	By default PPP looks in '/etc/ppp/options'
#
option /etc/ppp/options.pptpd

# TAG: debug
#	Turns on (more) debugging to syslog
#
#debug

# TAG: stimeout
#	Specifies timeout (in seconds) on starting ctrl connection
#
# stimeout 10

# TAG: noipparam
#       Suppress the passing of the client's IP address to PPP, which is
#       done by default otherwise.
#
#noipparam

# TAG: logwtmp
#	Use wtmp(5) to record client connections and disconnections.
#
logwtmp

# TAG: bcrelay <if>
#	Turns on broadcast relay to clients from interface <if>
#
#bcrelay eth1

# TAG: delegate
#	Delegates the allocation of client IP addresses to pppd.
#
#       Without this option, which is the default, pptpd manages the list of
#       IP addresses for clients and passes the next free address to pppd.
#       With this option, pptpd does not pass an address, and so pppd may use
#       radius or chap-secrets to allocate an address.
#
#delegate

# TAG: connections
#       Limits the number of client connections that may be accepted.
#
#       If pptpd is allocating IP addresses (e.g. delegate is not
#       used) then the number of connections is also limited by the
#       remoteip option.  The default is 100.
#connections 100

# TAG: localip
# TAG: remoteip
#	Specifies the local and remote IP address ranges.
#
#	These options are ignored if delegate option is set.
#
#       Any addresses work as long as the local machine takes care of the
#       routing.  But if you want to use MS-Windows networking, you should
#       use IP addresses out of the LAN address space and use the proxyarp
#       option in the pppd options file, or run bcrelay.
#
#	You can specify single IP addresses seperated by commas or you can
#	specify ranges, or both. For example:
#
#		192.168.0.234,192.168.0.245-249,192.168.0.254
#
#	IMPORTANT RESTRICTIONS:
#
#	1. No spaces are permitted between commas or within addresses.
#
#	2. If you give more IP addresses than the value of connections,
#	   it will start at the beginning of the list and go until it
#	   gets connections IPs.  Others will be ignored.
#
#	3. No shortcuts in ranges! ie. 234-8 does not mean 234 to 238,
#	   you must type 234-238 if you mean this.
#
#	4. If you give a single localIP, that's ok - all local IPs will
#	   be set to the given one. You MUST still give at least one remote
#	   IP for each simultaneous client.
#
# (Recommended)
localip 172.16.0.81
remoteip 172.16.168.1-254
# or
#localip 192.168.0.234-238,192.168.0.245
#remoteip 192.168.1.234-238,192.168.1.245

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