Figure 4-6. MTU and MRU settings

For Static IP, both MTU and MRU are set to 1500 bytes as default value. Note For DHCP, both MTU and MRU are set to 1500 bytes as default value.

For PPPoE, both MTU and MRU are set to 1492 bytes as default value.

¾DNS Server

DNS stands for Domain Name System. Every Internet host must have a unique IP address; also they may have a user-friendly, easy to remember name such as www.ippbx.com. The DNS server converts the user-friendly name into its equivalent IP address. The original DNS specifications require that each domain name is served by at least 2 DNS servers for redundancy. When you run your DNS, web, and mail servers all on the same MAChine - if this MAChine goes down, it doesn't really matter that the backup DNS server still works.

The recommended practice is to configure the primary and secondary DNS servers on separate MAChines, on separate Internet connections, and in separate geographic locations.

Figure 4-7. DNS server settings

Primary DNS Server

Sets the IP address of the primary DNS server.

Secondary DNS Server Sets the IP address of the secondary DNS server.

Table 4-2. DNS server description

¾Ping From WAN

Ping is a basic Internet program that lets you verify that a particular IP address exists and can accept requests. Ping is used diagnostically to ensure that a host computer you are trying to reach is actually operating.

The default setting is allowed user can ping the host computer from remote site. If you disallow, the host computer doesn’t response any user who issues Ping IP address command from any remote sites.

Figure 4-8. Ping from wan settings

44