SNR S2989G-48TX-DC [492/553] Dns troubleshooting

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S2989G-24TX Operation Manual

Chapter 9 Network Time Management Configuration

9-12

Figure 9-4 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 219.240.250.101

Switch(config)# dns-server 2001::1

Switch#ping host www.sina.com.cn

Switch#traceroute host www.sina.com.cn

Switch#telnet host www.sina.com.cn

Switch configuration for DNS SERVER:

Switch(config)# ip domain-lookup

Switch(config)# dns-server 219.240.250.101

Switch(config)# dns-server 2001::1

Switch(config)# ip dns server

9.3.4

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