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I have in my job a server running iptables and some clients needs to connect simultaneously in PPTP VPN connection.

My network:

  1. 2x internet connection, one ADSL+ 50 Mbps and Fiber Optic 100 Mbps.
  2. TP-LINK load balance router
  3. Squid 3.3.2 Proxy Transparent Server and Gateway with 2 network adapter.
  4. Squid 3.3.11 Proxy Transparent Server and Gateway Backup

The first Fiber Optic internet, are connected directly at with PPPoE authentication with Squid (at Squid start, automatically try to dial PPPoE connection and turn on firewall) and anyone use this internet connection to work at company.

The second is connected at (and in the future both internet connections will be here).

First test: Client computer with any ip, for example: with default gw Ok! Works and no worry - but no internet lock.

Second test: The same computer with default gateway to or, do not work - waiting for authentication to long and do not connect.

Third test: The same computer with default gateway at (proxy backup) and IPTABLES disabled, WORK, but not always!

iptables is configured to allow port TCP 1723 and 47 GRE protocol and forward packets.

IPTABLES proxy backup:

-A INPUT -o eth0 -j ALLOW
-A FORWARD -o eth0 -p 47 -j ALLOW
-A FORWARD -o eth0 -p tcp --dport 1723 -j ALLOW
-A OUTPUT -o eth0 -j ALLOW

Anyone can help?

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