User manual

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.

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.