ZyXEL Communications OLT2406, User Manual

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OLT2406 User’s Guide
126
C
HAPTER
12
MAC Forced Forwarding
12.1 Overview
Use MACFF (MAC Forced Forwarding) to control and forward traffic from hosts in the same subnet to a
predefined gateway. The OLT intercepts a host’s ARP (Address Resolution Protocol) requests and
forwards them to a predefined gateway. The gateway routes or forwards traffic so hosts in the same
subnet won’t know the internal server’s MAC addresses. A network administrator can use the predefined
gateway to monitor and manage hosts’ traffic. The OLT drops ARP replies from devices other than the
predefined gateway. This prevents attackers from getting MAC address information from your network
and enhances network security.
12.1.1 What You Need to Know
Read this section to know more about network size and subnet mask.
Network Size
The size of the network number determines the maximum number of possible hosts you can have on
your network. The larger the number of network number bits, the smaller the number of remaining host ID
bits.
An IP address with host IDs of all zeros is the IP address of the network (192.168.1.0 with a 24-bit subnet
mask, for example). An IP address with host IDs of all ones is the broadcast address for that network
(192.168.1.255 with a 24-bit subnet mask, for example).
As these two IP addresses cannot be used for individual hosts, calculate the maximum number of
possible hosts in a network as follows:
Notation
Since the mask is always a continuous number of ones beginning from the left, followed by a continuous
number of zeros for the remainder of the 32 bit mask, you can simply specify the number of ones instead
of writing the value of each octet. This is usually specified by writing a “/” followed by the number of bits
in the mask after the address.
For example, 192.1.1.0 /25 is equivalent to saying 192.1.1.0 with subnet mask 255.255.255.128.
Table 32 Maximum Host Numbers
SUBNET MASK HOST ID SIZE MAXIMUM NUMBER OF HOSTS
8 bits 255.0.0.0 24 bits 2
24
– 2 16777214
16 bits 255.255.0.0 16 bits 2
16
– 2 65534
24 bits 255.255.255.0 8 bits 2
8
– 2 254
29 bits 255.255.255.248 3 bits 2
3
– 2 6