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Chapter 10 Interface
ZyWALL USG 1000 User’s Guide
182
10.1.3 Interface Parameters
The ZyWALL restricts the amount of traffic into and out of the ZyWALL through each
interface.
• Upstream bandwidth is the amount of traffic from the ZyWALL through the interface to
the network.
• Downstream bandwidth is the amount of traffic from the network through the interface
into the ZyWALL.
2
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.
10.1.4 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.
• 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.
2. At the time of writing, the ZyWALL does not support downstream bandwidth management.
Table 46 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