TP-Link TL-WR841ND - Wireless N Router Atheros 2T2R 2.4GHz 802.11n 2.0 User Manual page 62

Firewall - A firewall protects your network from the outside world. Here you can enable or
disable the Router's firewall.
SPI Firewall - SPI (Stateful Packet Inspection, also known as dynamic packet filtering)
helps to prevent cyber attacks by tracking more state per session. It validates that the
traffic passing through the session conforms to the protocol. SPI Firewall is enabled by
factory default. If you want all the computers on the LAN exposed to the outside world,
you can disable it.
VPN - VPN Passthrough must be enabled if you want to allow VPN tunnels using IPSec,
PPTP, or L2TP protocols to pass through the Router's firewall.
PPTP Passthrough - Point-to-Point Tunneling Protocol (PPTP) allows the Point-to-Point
Protocol (PPP) to be tunneled through an IP network. To allow PPTP tunnels to pass
through the Router, keep the default, Enabled.
L2TP Passthrough - Layer 2 Tunneling Protocol (L2TP) is the method used to enable
Point-to-Point sessions via the Internet on the Layer 2 level. To allow L2TP tunnels to
pass through the Router, keep the default, Enabled.
IPSec Passthrough - Internet Protocol Security (IPSec) is a suite of protocols for
ensuring private, secure communications over Internet Protocol (IP) networks, through
the use of cryptographic security services. To allow IPSec tunnels to pass through the
Router, keep the default, Enabled.
ALG - It is recommended to enable Application Layer Gateway (ALG) because ALG allows
customized Network Address Translation (NAT) traversal filters to be plugged into the
TL-WR841N/TL-WR841ND
Figure 4-38 Basic Security
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Wireless N Router