ZyXEL NBG420N Manuel d'utilisateur télécharger pdf (Page 154)

Chapter 13 Firewall

NBG420N User’s Guide

154

The NBG420N is installed between the LAN and a broadband modem connecting to the

Internet. This allows it to act as a secure gateway for all data passing between the Internet and

the LAN.

The NBG420N has one Ethernet WAN port and four Ethernet LAN ports, which are used to

physically separate the network into two areas.The WAN (Wide Area Network) port attaches

to the broadband (cable or DSL) modem to the Internet.

The LAN (Local Area Network) port attaches to a network of computers, which needs security

from the outside world. These computers will have access to Internet services such as e-mail,

FTP and the World Wide Web. However, "inbound access" is not allowed (by default) unless

the remote host is authorized to use a specific service.

13.1.4 Guidelines For Enhancing Security With Your Firewall

1 Change the default password via web configurator.

2 Think about access control before you connect to the network in any way, including

attaching a modem to the port.

3 Limit who can access your router.

4 Don't enable any local service (such as SNMP or NTP) that you don't use. Any enabled

service could present a potential security risk. A determined hacker might be able to find

creative ways to misuse the enabled services to access the firewall or the network.

5 For local services that are enabled, protect against misuse. Protect by configuring the

services to communicate only with specific peers, and protect by configuring rules to

block packets for the services at specific interfaces.

6 Protect against IP spoofing by making sure the firewall is active.

7 Keep the firewall in a secured (locked) room.

13.2 Triangle Routes

If an alternate gateway on the LAN has an IP address in the same subnet as the NBG420N’s

LAN IP address, return traffic may not go through the NBG420N. This is called an

asymmetrical or “triangle” route. This causes the NBG420N to reset the connection, as the

connection has not been acknowledged.

You can have the NBG420N permit the use of asymmetrical route topology on the network

(not reset the connection).

Allowing asymmetrical routes may let traffic from the WAN go directly to the LAN without

passing through the NBG420N. A better solution is to use IP alias to put the NBG420N and

the backup gateway on separate subnets.

13.2.1 Triangle Routes and IP Alias

You can use IP alias instead of allowing triangle routes. IP Alias allow you to partition your

network into logical sections over the same interface.

By putting your LAN and Gateway A in different subnets, all returning network traffic must

pass through the NBG420N to your LAN. The following steps describe such a scenario.

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ZyXEL NBG420N Manuel d'utilisateur Page 154