Our Site to Site VPN Only works in 1 direction.

Posted on 2013-12-10
Last Modified: 2014-06-16
The VPN establishes fine, but does not work properly.

From the Main Site I can access the Network of the Branch Site fine.

The Branch Site cannot access the Network of the Main Site.

The Tracert when run on pc on the branch site, makes it to the router then times out.

The Tracert when run from the Router itself works fine.

Traceroute to, 30 hops max through WAN2 protocol ICMP
  1       50 ms
  2        50 ms

However from a PC in the branch site I cannot ping

Very strange, any ideas?

Main Site Settings ( Draytec Vigor 2860)
Has a Static IP from BT Infinity.

Call Direction  Dial-in

3. Dial-In Settings
Allowed Dial-In Type PPTP
Username 1
Password *************

5. TCP/IP Network Settings
Remote Gateway IP
Remote Mask
Local Network IP
Local Network Mask

RIP Direction TX/RX Both ( tried with it off too)
From first subnet to remote network off.

Branch Site Settings (Draytec 2850)

Call Direction Dial-Out
Always on Ticked
VPN Dial out Though WAN 2 only ( PPOE BT Modem BT Infinity)
Netbios Naming packet Pass
Muliticast Via VPN Pass( tested with Block too)

2, Dial Out Settings
Server IP Host Name for VPN
xxx.40.127.*** ( Main office static IP)
Username 1
Password ( Matches Main Office)

Remote Gateway IP
Remote Network IP
Remote Mask
Local IP
Local Mask

RIP Direction TX/RX Both

Branch site ( this looks ok!)

Routing Table
Key: C - connected, S - static, R - RIP, * - default, ~ - private
*            via    WAN2
C~  directly connected   VPN-2
S~    via  VPN-2
S  via     WAN2
C    directly connected    LAN1
C~    directly connected    LAN1
C~    directly connected    LAN2
*  via    WAN2
Question by:loughtec
LVL 77

Accepted Solution

arnold earned 500 total points
ID: 39710264
The reflection of the public IP suggests that there is an issue on the VPN setup.
Your VPN setup because of the use of the points to a remote type of VPN rather than a site to site.PPTP is a one way VPN.
LVL 25

Expert Comment

by:Fred Marshall
ID: 39710474
If the VPN device is not also the internet gateway on each side then consider this:

A packet from subnet A destined for subnet B has to be directed to the site A VPN device.
This is usually done with a route in the site A internet gateway.

The same thing applies for packets from subnet B:
A packet from subnet B destined for subnet A has to be directed to the site A VPN device.
This is usually done with a route in the site B internet gateway.

So, if this is true at only one end then this can happen:

A packet from subnet B destined for subnet A:
- first goes to the subnet B internet gateway
- it is routed to the subnet B VPN device
- it arrives at the subnet A VPN device
- it goes *directly* to the destination IP address without hitting the subnet A gateway.
- return packets (there are *always* return packets) will go to the subnet A gateway.
- the subnet A gateway should route them to the subnet A VPN device.
- from there, they should get to subnet B OK.

One thing that can mess this up is if the internet gateway device is using something like stateful packet filtering on the LAN interface(s).  Since it's not aware of the incoming packets, it will not forward the return packets.  Often this has to be turned off.

So, depending on how things are set up and which manufacturer's products are involved, this may be the sort of thing that you're seeing.

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