Technical Reference - ZyXEL Communications NXC2500 User Manual

8.4 Technical Reference

The following section contains additional technical information about the features described in this
chapter.
IP Address Assignment
Most interfaces have an IP address and a subnet mask. This information is used to create an entry
in the routing table.
In most interfaces, you can enter the IP address and subnet mask manually.
In many interfaces, you can also let the IP address and subnet mask be assigned by an external
DHCP server on the network. In this case, the interface is a DHCP client. Virtual interfaces,
however, cannot be DHCP clients. You have to assign the IP address and subnet mask manually.
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 NXC 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 NXC 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 NXC creates the following entry in the
routing table.
Table 57 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 NXC
uses the gateway with the lowest metric, or cost. If two or more gateways have the same metric,
the NXC uses the one that was set up first (the first entry in the routing table).
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 NXC restricts the amount of traffic into and out of the NXC through each interface.
• Egress bandwidth sets the amount of traffic the NXC sends out through the interface to the
network.
• Ingress bandwidth sets the amount of traffic the NXC allows in through the interface from the
1
network.
If you set the bandwidth restrictions very high, you effectively remove the restrictions.
The NXC 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 NXC divides
1. At the time of writing, the NXC does not support ingress bandwidth management.
NXC2500 User's Guide
DESTINATION
200.200.200.100
Chapter 8 Interfaces
121