Manual

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DNS SERVER typical environment
The figure above is an application of DNS SERVER. Under some circumstances, the client PC
doesn’t know the real DNS SERVER, and points to the switch instead. The switch plays the
role of a DNS SERVER in two steps: Enable the global DNS SERVER function, configure the
IP address of the real DNS server. After the DNS SERVER function is globally enabled, the
switch will look up its local cache when receiving a DNS request from a client PC. If there is a
domain needed by the local client, it will directly answer the client’s request; otherwise, the
switch will relay the request to the real DNS server, pass the reply from the DNS Server to the
client and record the domain and its IP address for a faster lookup in the future.
Switch configuration for DNS CLIENT:
Switch(config)# ip domain-lookup
Switch(config)# dns-server 87.250.250.3
Switch(config)# dns-server 2001::1
Switch#ping host www.yandex.ru
Switch#traceroute host www.yandex.ru
Switch#telnet host www.yandex.ru
Switch configuration for DNS SERVER:
Switch(config)# ip domain-lookup
Switch(config)# dns-server 87.250.250.3
Switch(config)# dns-server 2001::1
Switch(config)# ip dns server
41.4 DNS Troubleshooting
In configuring and using DNS, the DNS may fail due to reasons such as physical connection
failure or wrong configurations. The user should ensure the following:
First make sure good condition of the TACACS+ server physical connection;
Second all interface and link protocols are in the UP state (use “show interface” command);
Then please make sure that the DNS dynamic lookup function is enabled (use the “ip domain-
lookup” command) before enabling the DNS CLIENT function. To use DNS SERVER function,
please enable it (use the “ip dns server” command);
Finally ensure configured DNS server address (use “dns-server” command), and the switch
can ping DNS server;
If the DNS problems remain unsolved, please use debug DNS all and other debugging
command and copy the DEBUG message within 3 minutes, send the recorded message to the
technical service center of our company.