ZyXEL Communications Unified Security Gateway ZyWALL 300, User Manual

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Chapter 13 Interfaces
ZyWALL USG 300 User’s Guide
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• 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
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.
1. At the time of writing, the ZyWALL does not support ingress bandwidth management.