ZyXEL Communications ZyWall ATP series User Manual page 296

In general, the IP address and subnet mask of each interface should not overlap, though it is possible for
this to happen with DHCP clients.
In the example above, if the Zyxel Device gets a packet with a destination address of 5.5.5.5, it might
not find any entries in the routing table. In this case, the packet is dropped. However, if there is a default
router to which the Zyxel Device should send this packet, you can specify it as a gateway in one of the
interfaces. For example, if there is a default router at 200.200.200.100, you can create a gateway at
200.200.200.100 on ge2. In this case, the Zyxel Device creates the following entry in the routing table.
Table 118 Example: Routing Table Entry for a Gateway
IP ADDRESS(ES)
0.0.0.0/0
The gateway is an optional setting for each interface. If there is more than one gateway, the Zyxel
Device uses the gateway with the lowest metric, or cost. If two or more gateways have the same metric,
the Zyxel Device uses the one that was set up first (the first entry in the routing table). In PPPoE/PPTP/L2TP
interfaces, the other computer is the gateway for the interface by default. In this case, you should
specify the metric.
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 Zyxel Device restricts the amount of traffic into and out of the Zyxel Device through each interface.
• Egress bandwidth sets the amount of traffic the Zyxel Device sends out through the interface to the
network.
• Ingress bandwidth sets the amount of traffic the Zyxel Device allows in through the interface from the
network.At the time of writing, the Zyxel Device does not support ingress bandwidth management.
If you set the bandwidth restrictions very high, you effectively remove the restrictions.
The Zyxel Device 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 Zyxel
Device 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.
Chapter 9 Interfaces
DESTINATION
200.200.200.100
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