ELSA Cable - Manual (Page 40)

Operating modes and functions
ELSA MicroLink Cable
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But this provokes objections from the network manager responsible for the security of
data on the company's network: Every workstation computer on the WWW? Surely this
means that anyone can get in from outside?—Not true!
IP masquerading provides a hiding place for every computer while connected with the
Internet. Only the router module of the unit and its IP address are visible on the Internet.
The computers in the LAN then use the router as a gateway so that they themselves
cannot be detected. To do this, the router separates Internet and intranet, as if by a wall.
Therefore, IP masquerading is also called a “firewall function“.
For further information, see the 'IP Routing: IP masquerading' section.
IP routing
This chapter describes the function of the cable modem as an IP router. Whenever the
IP router (or simply the router) is mentioned in the next paragraphs, this is a reference to
the corresponding operating mode of the cable modem.
An IP router works between networks which use TCP/IP as the network protocol. This
only allows data transmissions to destination addresses entered in the routing table.
This chapter explains the structure of the IP routing table of an ELSA router, as well as
the additional functions available to support IP routing.
The IP routing table
Use the IP routing table to tell the router which remote station (which other router or
computer) it should send the data for particular IP addresses or IP address ranges to. This
type of entry is also known as a “route“ since it is used to describe the path of the data
packet. This procedure is also called “static routing“ since you make these entries
yourself and they remain unchanged until you either change or delete them yourself.
Naturally, there is also “dynamic routing“ too. The routers use the routes in this way to
exchange data between themselves and continually update it automatically. The static
routing table can hold up to 64 entries, the dynamic table can hold 128. The IP router
looks at both tables when the IP/RIP is activated.
The routing table can be found in the configuration tool ELSA LANconfig in the 'TCP/IP'
configuration section on the 'Router' tab, or in the /Setup/IP router/IP
routing menu. This, then, is how an IP routing table might look:
IP address IP netmask Router Dis-
tance
192.168.0.0 255.255.0.0 0.0.0.0 0
172.16.0.0 255.255.0.0 0.0.0.0 0
10.0.0.0 255.0.0.0 0.0.0.0 0