ZyXEL Communications UAG4100 User Manual page 149

In the example above, if the UAG 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 UAG 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 wan1. In this case, the UAG creates the following entry in the
routing table.
Table 66 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 UAG
uses the gateway with the lowest metric, or cost. If two or more gateways have the same metric,
the UAG uses the one that was set up first (the first entry in the routing table). In PPPoE/PPTP
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 UAG restricts the amount of traffic into and out of the UAG through each interface.
• Egress bandwidth sets the amount of traffic the UAG sends out through the interface to the
network.
• Ingress bandwidth sets the amount of traffic the UAG allows in through the interface from the
1
network.
If you set the bandwidth restrictions very high, you effectively remove the restrictions.
The UAG 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 UAG 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.
1. At the time of writing, the UAG does not support ingress bandwidth management.
Chapter 10 Interfaces
DESTINATION
200.200.200.100
UAG4100 User's Guide
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