Planet Technology Internet Telephony PBX System IPX-1900 - Manual (Page 43)

called www.IP-PBX.com. When we need to find the host name from an IP address we send a request
to the host using its IP address. The host will respond with its host name.
¾ WAN Port MAC
The MAC (Media Access Control) Address field is required by some Internet Service Providers (ISP).
The default MAC address is set to the MAC address of the WAN interface in the device. It is only
necessary to fill the field if required by your ISP.
The WAN port allows your voice gateway to be connected to an Internet Access Device, e.g. router,
cable modem, ADSL modem, through a CAT.5 twisted pair Ethernet Cable. MAC addresses are
uniquely set by the network adapter manufacturer and are sometimes called "physical addresses" for
this reason. MAC assigns a unique number to each IP network adapter called the MAC address. The
MAC address is commonly written as a sequence of 12 hexadecimal digits as follows:
00:3f:4f:88:81:18 . The first six hexadecimal digits of the address correspond to a manufacturer's
unique identifier, while the last six digits correspond to the device's serial number.
Some Internet service providers track the MAC address of a home router for security purposes. Many
routers support a process called cloning that allows the MAC address to be simulated so that it
matches one the service provider is expecting. This allows end-user to change their router (and their
real MAC address) without having to notify the provider. For example, you could allow packets which
have your name server's IP on them, but come from another MAC address (one way of spoofing
packets).
Figure 4-5. WAN port MAC settings
¾ MTU and MRU
MTU stands for Maximum Transmission Unit, the largest physical packet size, measured in bytes that a
network can transmit. Any messages larger than the MTU are divided into smaller packets before being
sent.
MRU stands for Maximum Receiving Unit. The largest physical packet size, measured in bytes that a
network can receive. Any messages larger than the MRU are divided into smaller packets before being
received.
The key is to be deciding how big your bandwidth pipe is and select the best MTU for your configuration.
For example, you have a 33.6 modem, you use a MTU and MRU of 576, and if you have a larger pipe
you may want to try 1500.
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