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Page 541 / 998 Scroll up to view Page 536 - 540
DHCP Relay Command Reference
Dynamic Host Configuration Protocol
5-81
iMG/RG Software Reference Manual (System Administration)
5.1.7.1.2 DHCPRELAY CLEAR SERVERS
Syntax
dhcprelay clear servers
Description
This command deletes all DHCP server IP addresses stored in DHCP relay's list of server
IP addresses.
Example
--> dhcprelay clear servers
See also
dhcprelay delete server
5.1.7.1.3 DHCPRELAY DELETE SERVER
Syntax
DHCPRELAY DELETE SERVER <NUMBER>
Description
This command deletes a single DHCP server address stored in the DHCP relay's list of
server IP addresses.
Options
The following table gives the range of values for each option which can be specified with
this command and a default value (if applicable).
Example
--> dhcprelay delete server 3
See also
dhcprelay list servers
dhcprelay clear servers
5.1.7.1.4 DHCPRELAY ENABLE|DISABLE
Syntax
DHCPRELAY {ENABLE|DISABLE}
Description
This command enables/disables DHCP relay.
DHCP relay must be enabled in order to carry out any DHCP relay configuration.
Note:
DHCP relay and DHCP server cannot be enabled at the same time. Trying to configure DHCP relay when
DHCP server is enabled results in CLI warning message.
Options
The following table gives the range of values for each option which can be specified with
this command and a default value (if applicable).
Option
Description
Default Value
number
A number that identifies the DHCP server in the
DHCP relay’s list of servers. To display server num-
bers, use the dhcprelay list servers command.
N/A
Page 542 / 998
Dynamic Host Configuration Protocol
DHCP Relay Command Reference
iMG/RG Software Reference Manual (System Administration)
5-82
Example
--> dhcprelay enable
See also
dhcpserver enable|disable
5.1.7.1.5 DHCPRELAY LIST SERVERS
Syntax
DHCPRELAY LIST SERVERS
Description
This command displays the DHCP relay's list of DHCP server IP addresses with their
identification numbers.
Example
--> dhcprelay list servers
DHCP Servers:
ID
| IP Address
-----|------------------
1 | 192.168.102.3
2 | 239.252.197.0
------------------------
See also
dhcpserver list subnets
5.1.7.1.6 DHCPRELAY SHOW
Syntax
DHCPRELAY SHOW
Description
This command tells you whether DHCP relay is enabled or disabled.
Example
--> dhcprelay show server
Global DHCP Relay Configuration:
Status: ENABLED
See also
DHCPRELAY ENABLE|DISABLE
5.1.7.1.7 DHCPRELAY UPDATE
Syntax
DHCPRELAY UPDATE
Option
Description
Default Value
enable
Enables configuration of DHCP relay.
enable
disable
Disables configuration of DHCP relay.
enable
Page 543 / 998
DHCP Relay Command Reference
Domain name system - DNS
5-83
iMG/RG Software Reference Manual (System Administration)
Description
This command updates the DHCP relay configuration. Changes made to the relay config-
uration will not take effect until this command has been entered.
Example
--> dhcprelay update
dhcprelay: Reset request acknowledged. Reset imminent.
5.2
Domain name system - DNS
DNS is an abbreviation for Domain Name System, a system for naming computers and network services that is
organized into a hierarchy of domains. DNS naming is used in TCP/IP networks, such as the Internet, to locate
computers and services through user-friendly names. When a user enters a DNS name in an application, DNS
services can resolve the name to other information associated with the name, such as an IP address.
For example, most users prefer a friendly name such as
alliedtelesyn.com
to locate a computer such as a mail or
Web server on a network. A friendly name can be easier to learn and remember. However, computers commu-
nicate over a network by using numeric addresses. To make use of network resources easier, name services
such as DNS provide a way to map the user-friendly name for a computer or service to its numeric address. If
you have ever used a Web browser, you have used DNS.
The following graphic shows a basic use of DNS, which is finding the IP address of a computer based on its
name.
FIGURE 5-1
Domain Name System
In this example, a client computer queries a server, asking for the IP address of a computer configured to use
host.alliedtelesyn.com as its DNS domain name. Because the server is able to answer the query based on its
local database, it replies with an answer containing the requested information, which is a host (A) resource
record that contains the IP address information for
host.alliedtelesyn.com
. The example shows a simple DNS
query between a single client and server. In practice, DNS queries can be more involved than this and include
additional steps not shown here.
DNS Client
DNS Server
What is IP address for host.alliedtelesis.com?
host.alliedtelesis.com = 192.168.1.20
DNS Server Data
host.alliedtelesis.com
192.168.1.20
Page 544 / 998
Domain name system - DNS
DNS Relay
iMG/RG Software Reference Manual (System Administration)
5-84
5.2.1
DNS Relay
gateway can act as a DNS relay. So, DNS packets that arrive at the Residential Gateway, addressed to the Resi-
dential Gateway, will be relayed on to a known DNS Server.
In this way, devices on the LAN can treat the Residential Gateway as though it were the DNS Server. Only the
Residential Gateway needs to know the address of the real DNS Server looking into it is internal DNS Relay
servers list.
It's possible configure the DHCP server running on the internal Residential Gateway's IP interface in order to
offer the IP address of it's internal IP interface as DNS server's IP address for the internal hosts DNS requests.
It's also possible write a file named
dnsrelaylandb
with information about host attributes and a domain name
and IP address mask. When DNS relay will receive a DNS request it will check if the answer to this request is
in this file and in this case it will answer to the question; if it hasn’t enough information it will forward the
request to a DNS server.
It is possible to nominate both a primary and a secondary DNS server to contact. DNS responses received
from the server are then forwarded back to the original host making the DHCP request.
Both UDP and TCP DNS requests are supported.
The DNS relay does not bind itself to any one specific interface or interface type, but rather will listen for traf-
fic on all available IP interfaces. It relies on the well known UDP and TCP port number for a DNS server (port
number 53) for receiving DNS traffic.
5.2.2
DNS Client
The ggatewayateway is provided with an internal DNS client, to use this function you must add DNS server
addresses that will be used by the Residential Gateway ONLY for its own lookups.
5.2.3
DNS Relay command reference
This section describes the commands available on the gateway to enable, configure and manage the DNS Relay
module.
5.2.3.1 DNS Relay CLI commands
The table below lists the
DNSrelay
commands provided by the CLI:
Page 545 / 998
DNS Relay command reference
Domain name system - DNS
5-85
iMG/RG Software Reference Manual (System Administration)
TABLE 5-4
DNS Relay Commands
5.2.3.1.1 DNSRELAY ADD LOCALDATABASE
Syntax
DNSRELAY ADD LOCALDATABASE <database> HOSTNAME <name> IPAD-
DRSESS <ipaddress>
Description
This command create a local database specifying hostname and IP address.
Options
The following table gives the range of values for each option that can be specified with
this command and a default value (if applicable).
Commands
Fiber
A
Fiber
B
Fiber
C
Fiber
D
Fiber
E
Modular
ADSL
A
ADSL
B
ADSL
C
DNSRELAY ADD LOCALDATABASE
X
X
X
X
X
X
X
X
X
DNSRELAY ADD SERVER
X
X
X
X
X
X
X
X
X
DNSRELAY CLEAR SERVERS
X
X
X
X
X
X
X
X
X
DNSRELAY DELETE SERVER
X
X
X
X
X
X
X
X
X
DNSRELAY ENABLE|DISABLE
X
X
X
X
X
X
X
X
X
DNSRELAY ENABLE|DISABLE
X
X
X
X
X
X
X
X
X
DNSRELAY SHOW
X
X
X
X
X
X
X
X
X
DNSRELAY LIST SERVERS
X
X
X
X
X
X
X
X
X
DNSRELAY SET HOSTNAME
X
X
X
X
X
X
X
X
X
DNSRELAY SET DYNAMICSERVERPRIORITY
X
X
X
X
X
X
X
X
X
DNSRELAY SET LANDOMAINNAME
X
X
X
X
X
X
X
X
X
DNSRELAY SHOW LANDOMAINNAME
X
X
X
X
X
X
X
X
X
Option
Description
Default Value
database
The name of the database
N/A
name
The name of the host
N/A
ip-address
The IP address of a the host
0.0.0.0

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