ZyXEL Communications MAX-200M1 Series, User Manual

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ZyXEL MAX-200M1 Series User’s Guide
Chapter 8 LAN 85
If the Primary and Secondary DNS Server fields in the LAN Setup screen are not specified,
for instance, left as 0.0.0.0, the ZyXEL Device tells the DHCP clients that it itself is the DNS
server. When a computer sends a DNS query to the ZyXEL Device, the ZyXEL Device
forwards the query to the real DNS server learned through IPCP and relays the response back
to the computer.
Please note that DNS proxy works only when the ISP uses the IPCP DNS server extensions. It
does not mean you can leave the DNS servers out of the DHCP setup under all circumstances.
If your ISP gives you explicit DNS servers, make sure that you enter their IP addresses in the
LAN Setup screen. This way, the ZyXEL Device can pass the DNS servers to the computers
and the computers can query the DNS server directly without the ZyXEL Device’s
intervention.
8.1.5 RIP Setup
RIP (Routing Information Protocol) allows a router to exchange routing information with
other routers. The
RIP Direction field controls the sending and receiving of RIP packets.
When set to:
• Both - the ZyXEL Device will broadcast its routing table periodically and incorporate the
RIP information that it receives.
• In Only - the ZyXEL Device will not send any RIP packets but will accept all RIP
packets received.
• Out Only - the ZyXEL Device will send out RIP packets but will not accept any RIP
packets received.
• None - the ZyXEL Device will not send any RIP packets and will ignore any RIP packets
received.
The Version field controls the format and the broadcasting method of the RIP packets that the
ZyXEL Device sends (it recognizes both formats when receiving). RIP-1 is universally
supported; but RIP-2 carries more information. RIP-1 is probably adequate for most networks,
unless you have an unusual network topology.
Both RIP-2B and RIP-2M sends the routing data in RIP-2 format; the difference being that
RIP-2B uses subnet broadcasting while RIP-2M uses multicasting.
8.1.6 Multicast
Traditionally, IP packets are transmitted in one of either two ways - Unicast (1 sender - 1
recipient) or Broadcast (1 sender - everybody on the network). Multicast delivers IP packets to
a group of hosts on the network - not everybody and not just 1.
IGMP (Internet Group Multicast Protocol) is a network-layer protocol used to establish
membership in a Multicast group - it is not used to carry user data. IGMP version 2 (RFC
2236) is an improvement over version 1 (RFC 1112) but IGMP version 1 is still in wide use. If
you would like to read more detailed information about interoperability between IGMP
version 2 and version 1, please see sections 4 and 5 of RFC 2236. The class D IP address is
used to identify host groups and can be in the range 224.0.0.0 to 239.255.255.255. The address