ZyXEL Communications Prestige 642R Series User Manual Download

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Prestige 642R Series ADSL Router

3-4

Internet Access

servers are conveyed through IPCP negotiation. The Prestige supports the IPCP DNS server extensions
through the DNS proxy feature.
If the

Primary

and

Secondary DNS Server

fields in

DHCP Setup

are not

specified, i.e., left as 0.0.0.0, the

Prestige tells the DHCP clients that it itself is the DNS server. When a workstation sends a DNS query to the
Prestige, the Prestige forwards the query to the real DNS server learned through IPCP and relays the response
back to the workstation.
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

DHCP Setup

menu. This way, the

Prestige can pass the DNS servers to the workstations and the workstations can query the DNS server directly
without the Prestige’s intervention.

3.4 IP

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 is a third way to deliver IP packets to

a group

hosts on the network - not everybody.
IGMP (Internet Group Multicast Protocol) is a session-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 224.0.0.0 is not assigned to any group and is used by IP multicast computers.
The address 224.0.0.1 is used for query messages and is assigned to the permanent group of all IP hosts
(including gateways). All hosts must join the 224.0.0.1 group in order to participate in IGMP. The address
224.0.0.2 is assigned to the multicast routers group.
The Prestige supports both IGMP version 1 (

IGMP-v1

) and version 2 (

IGMP-v2

)

. At start up, the Prestige

queries all directly connected networks to gather group membership. After that, the Prestige periodically
updates this information. IP Multicasting can be enabled/disabled on the Prestige LAN and/or WAN
interfaces using menus 3.2 (LAN) and 11.3 (WAN). Select

None

to disable IP Multicasting on these

interfaces.

3.5 IP

Policies

Traditionally, routing is based on the destination address

only

and the router takes the shortest path to

forward a packet. IP Policy Routing (IPPR) provides a mechanism to override the default routing behavior
and alter the packet forwarding based on the policy defined by the network administrator. Policy-based
routing is applied to incoming packets on a per interface basis, prior to the normal routing. Create policies
using SMT Menu 25 (

see the IP Policy Routing chapter in Part 3

) and apply them on the Prestige LAN

and/or WAN interfaces using menus 3.2 (LAN) and 11.3 (WAN).