ZyXEL Communications USG40 User Manual page 356

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/USG restricts the amount of traffic into and out of the ZyWALL/USG through each
interface.
• Egress bandwidth sets the amount of traffic the ZyWALL/USG sends out through the interface to
the network.
• Ingress bandwidth sets the amount of traffic the ZyWALL/USG allows in through the interface
from the network.At the time of writing, the ZyWALL/USG does not support ingress bandwidth
management.
If you set the bandwidth restrictions very high, you effectively remove the restrictions.
The ZyWALL/USG 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/USG 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/USG, 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.
Chapter 10 Interfaces
ZyWALL/USG Series User's Guide
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