Chapter 10 Interface

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.

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

 

 

 

 

 

 

 

 

2.At the time of writing, the ZyWALL does not support downstream bandwidth management.

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ZyWALL USG 1000 User’s Guide