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Page 266 / 944 Scroll up to view Page 261 - 265
Chapter 11 Interfaces
ZyWALL USG 50 User’s Guide
266
11.8
Interface Technical Reference
Here is more detailed information about interfaces on the ZyWALL.
IP Address Assignment
Most interfaces have an IP address and a subnet mask. This information is used to
create an entry in the routing table.
Figure 167
Example: Entry in the Routing Table Derived from Interfaces
For example, if the ZyWALL gets a packet with a destination address of
100.100.25.25, it routes the packet to interface lan1. If the ZyWALL gets a packet
with a destination address of 200.200.200.200, it routes the packet to interface
wan1.
In most interfaces, you can enter the IP address and subnet mask manually. In
PPPoE/PPTP interfaces, however, the subnet mask is always 255.255.255.255
Egress
Bandwidth
Enter the maximum amount of traffic, in kilobits per second, the
ZyWALL can send through the interface to the network. Allowed
values are 0 - 1048576.
Ingress
Bandwidth
This is reserved for future use.
Enter the maximum amount of traffic, in kilobits per second, the
ZyWALL can receive from the network through the interface. Allowed
values are 0 - 1048576.
OK
Click
OK
to save your changes back to the ZyWALL.
Cancel
Click
Cancel
to exit this screen without saving.
Table 69
Configuration > Network > Interface > Add (continued)
LABEL
DESCRIPTION
Table 70
Example: Routing Table Entries for Interfaces
IP ADDRESS(ES)
DESTINATION
100.100.1.1/16
lan1
200.200.200.1/24
wan1
lan1
wan1
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267
because it is a point-to-point interface. For these interfaces, you can only enter
the IP address.
In many interfaces, you can also let the IP address and subnet mask be assigned
by an external DHCP server on the network. In this case, the interface is a DHCP
client. Virtual interfaces, however, cannot be DHCP clients. You have to assign the
IP address and subnet mask manually.
In general, the IP address and subnet mask of each interface should not overlap,
though it is possible for this to happen with DHCP clients.
In the example above, if the ZyWALL gets a packet with a destination address of
5.5.5.5, it might not find any entries in the routing table. In this case, the packet
is dropped. However, if there is a default router to which the ZyWALL should send
this packet, you can specify it as a gateway in one of the interfaces. For example,
if there is a default router at 200.200.200.100, you can create a gateway at
200.200.200.100 on ge2. In this case, the ZyWALL creates the following entry in
the routing table.
The gateway is an optional setting for each interface. If there is more than one
gateway, the ZyWALL uses the gateway with the lowest metric, or cost. If two or
more gateways have the same metric, the ZyWALL uses the one that was set up
first (the first entry in the routing table). In PPPoE/PPTP interfaces, the other
computer is the gateway for the interface by default. In this case, you should
specify the metric.
If the interface gets its IP address and subnet mask from a DHCP server, the DHCP
server also specifies the gateway, if any.
Interface Parameters
The ZyWALL restricts the amount of traffic into and out of the ZyWALL through
each interface.
•
Egress bandwidth sets the amount of traffic the ZyWALL sends out through the
interface to the network.
•
Ingress bandwidth sets the amount of traffic the ZyWALL allows in through the
interface from the network.
1
Table 71
Example: Routing Table Entry for a Gateway
IP ADDRESS(ES)
DESTINATION
0.0.0.0/0
200.200.200.10
0
1.
At the time of writing, the ZyWALL does not support ingress bandwidth management.
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Chapter 11 Interfaces
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268
If you set the bandwidth restrictions very high, you effectively remove the
restrictions.
The ZyWALL also restricts the size of each data packet. The maximum number of
bytes in each packet is called the maximum transmission unit (MTU). If a packet is
larger than the MTU, the ZyWALL divides it into smaller fragments. Each fragment
is sent separately, and the original packet is re-assembled later. The smaller the
MTU, the more fragments sent, and the more work required to re-assemble
packets correctly. On the other hand, some communication channels, such as
Ethernet over ATM, might not be able to handle large data packets.
DHCP Settings
Dynamic Host Configuration Protocol (DHCP, RFC 2131, RFC 2132) provides a way
to automatically set up and maintain IP addresses, subnet masks, gateways, and
some network information (such as the IP addresses of DNS servers) on
computers in the network. This reduces the amount of manual configuration you
have to do and usually uses available IP addresses more efficiently.
In DHCP, every network has at least one DHCP server. When a computer (a DHCP
client) joins the network, it submits a DHCP request. The DHCP servers get the
request; assign an IP address; and provide the IP address, subnet mask, gateway,
and available network information to the DHCP client. When the DHCP client
leaves the network, the DHCP servers can assign its IP address to another DHCP
client.
In the ZyWALL, some interfaces can provide DHCP services to the network. In this
case, the interface can be a DHCP relay or a DHCP server.
As a DHCP relay, the interface routes DHCP requests to DHCP servers on different
networks. You can specify more than one DHCP server. If you do, the interface
routes DHCP requests to all of them. It is possible for an interface to be a DHCP
relay and a DHCP client simultaneously.
As a DHCP server, the interface provides the following information to DHCP clients.
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Chapter 11 Interfaces
ZyWALL USG 50 User’s Guide
269
•
IP address - If the DHCP client’s MAC address is in the ZyWALL’s static DHCP
table, the interface assigns the corresponding IP address. If not, the interface
assigns IP addresses from a pool, defined by the starting address of the pool
and the pool size.
The ZyWALL cannot assign the first address (network address) or the last
address (broadcast address) in the subnet defined by the interface’s IP address
and subnet mask. For example, in the first entry, if the subnet mask is
255.255.255.0, the ZyWALL cannot assign 50.50.50.0 or 50.50.50.255. If the
subnet mask is 255.255.0.0, the ZyWALL cannot assign 50.50.0.0 or
50.50.255.255. Otherwise, it can assign every IP address in the range, except
the interface’s IP address.
If you do not specify the starting address or the pool size, the interface the
maximum range of IP addresses allowed by the interface’s IP address and
subnet mask. For example, if the interface’s IP address is 9.9.9.1 and subnet
mask is 255.255.255.0, the starting IP address in the pool is 9.9.9.2, and the
pool size is 253.
•
Subnet mask - The interface provides the same subnet mask you specify for the
interface. See
IP Address Assignment on page 266
.
•
Gateway - The interface provides the same gateway you specify for the
interface. See
IP Address Assignment on page 266
.
•
DNS servers - The interface provides IP addresses for up to three DNS servers
that provide DNS services for DHCP clients. You can specify each IP address
manually (for example, a company’s own DNS server), or you can refer to DNS
servers that other interfaces received from DHCP servers (for example, a DNS
server at an ISP). These other interfaces have to be DHCP clients.
It is not possible for an interface to be the DHCP server and a DHCP client
simultaneously.
WINS
WINS (Windows Internet Naming Service) is a Windows implementation of
NetBIOS Name Server (NBNS) on Windows. It keeps track of NetBIOS computer
names. It stores a mapping table of your network’s computer names and IP
addresses. The table is dynamically updated for IP addresses assigned by DHCP.
This helps reduce broadcast traffic since computers can query the server instead
of broadcasting a request for a computer name’s IP address. In this way WINS is
similar to DNS, although WINS does not use a hierarchy (unlike DNS). A network
can have more than one WINS server. Samba can also serve as a WINS server.
Table 72
Example: Assigning IP Addresses from a Pool
START IP ADDRESS
POOL SIZE
RANGE OF ASSIGNED IP ADDRESS
50.50.50.33
5
50.50.50.33 - 50.50.50.37
75.75.75.1
200
75.75.75.1 - 75.75.75.200
99.99.1.1
1023
99.99.1.1 - 99.99.4.255
120.120.120.100
100
120.120.120.100 - 120.120.120.199
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270
PPPoE/PPTP Overview
Point-to-Point Protocol over Ethernet (PPPoE, RFC 2516) and Point-to-Point
Tunneling Protocol (PPTP, RFC 2637) are usually used to connect two computers
over phone lines or broadband connections. PPPoE is often used with cable
modems and DSL connections. It provides the following advantages:
•
The access and authentication method works with existing systems, including
RADIUS.
•
You can access one of several network services. This makes it easier for the
service provider to offer the service
•
PPPoE does not usually require any special configuration of the modem.
PPTP is used to set up virtual private networks (VPN) in unsecure TCP/IP
environments. It sets up two sessions.
1
The first one runs on TCP port 1723. It is used to start and manage the second
one.
2
The second one uses Generic Routing Encapsulation (GRE, RFC 2890) to transfer
information between the computers.
PPTP is convenient and easy-to-use, but you have to make sure that firewalls
support both PPTP sessions.

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