User's Manual

74-4
debug dns {all | packet [send | recv] |
events | relay}
no debug dns {all | packet [send | recv]
| events | relay}
To enable/disable DEBUG of DNS function.
74.3 Typical Examples of DNS
Figure
74-1 DNS CLIENT typical environment
As shown in fig, the switch connected to DNS server through network, if the switch want to visit sina Website,
it needn’t to know the IPv4/IPv6 address of sina Website, only need is to record the domain name of sina
Website is www.sina.com.cn. The DNS server can resolute out the IPv4/IPv6 address of this domain name
and send to switch, then the switch can visit sina Website correctly. The switch is configured as DNS client,
basic configurations are as below: first to enable DNS dynamic domain name resolution function on switch,
and configure DNS server address, then with some kinds of tools such as PING, the switch can get
corresponding IPv4/IPv6 address with dynamic domain name resolution function.
Figure 74-2 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
DNS SERVER
IP:219.240.250.101
IPv6:2001::1
INTERNET
SWITCH
client
DNS SERVER
IP: 219.240.250.101
IPv6: 2001::1
ip domain-lookup
dns-server 219.240.250.101
dns-server 2001::1
SWITCH
INTERNET