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Chapter 4: Using the X5v’s Advanced Firewall 51
4
Using the X5v’s Advanced
Firewall
In addition to the security provided by NAT, the X5v includes
an advanced firewall. This chapter describes the firewall and
the types of protection it offers. If you are like most users, you
probably will not need to modify your firewall settings. If,
however, you are an administrator or an expert user who wants
to customize the firewall to protect a network against specific
threats, you should refer to this chapter.
You can think of the firewall as playing a role like that of a guard at
the gate of an ancient walled city. The guard has a great scroll,
which lists allowed and proscribed traffic. In one possible set of
rules, visitors may enter only if they show an invitation from a
citizen of the city. Children may not leave the city. The guard may
allow entry of carts of flour, but only for delivery to the bakery.
Any messenger who doesn’t know the password to the city is
thrown in the moat, and can’t pass through the gate.
You may set the policies of your firewall, which is like writing the
rules on the great scroll in the example. The firewall will then
follow the rules, acting like the guard. Instead of controlling entry
and exit of goods and people, you control entry and exit of
particular types of IP packets. In general, you will want to do this
to prevent unwanted packets from entering your network (this is
the purpose of the wall in the first place).
By default, the firewall will allow only those packets to enter that
you are likely to need; for example, in response to a request for a
web page, or as part of a VoIP call you make. You may want to
accept other, specific packets, perhaps to facilitate Internet gaming,
or because you want people outside your network to access a server