CCNA: DNS, DHCP, and NTP

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Description:

Configuring DNS, DHCP, and NTP on Cisco Routers

To define static hosts

R1(config)#ip host TEST-HOST 10.0.0.3
R1(config)#ipv6 host TEST-HOST 3FFF:1234:ABCD:1::3
R1(config)#end
R1#show hosts

Configuring DNS

Router(config)#no ip domain-lookup # disables dns lookups, good for practicing but not in real world
Router(config)#ip domain-lookup # enabled by default, this shows DNS as running
Router(config)#ip name-server # sets a dns server, can use multiple
R1(config)#ip name-server 192.168.1.2
R1(config)#ip name-server 3FFF:1234:ABCD:1::2 # ipv6

Show Commands:

show hosts
debug domain

Configure DHCP:

Router#configure terminal
Router(config)#service dhcp
#The next step is to create a DHCP pool which defines the IP address pool that will be allocated to clients.
#In this example, pool name “SUBNET_A” will offer IP addresses from the 192.168.1.0/24 range:
Router(config)#ip dhcp pool SUBNET_A
Router(dhcp-config)#network 192.168.1.0 255.255.255.0
Router(dhcp-config)#default-router 192.168.1.1
Router(dhcp-config)#dns-server 8.8.8.8
Router(dhcp-config)#domain-name mydomain.net # didn't work in packet tracer, probably work on router
Router(dhcp-config)#lease 30 # didn't work in packet tracer switch, probably work on router
Router(dhcp-config)#end
Router#show ip dhcp binding

To exclude a single address or a range of addresses, use the following:

Router(config)#ip dhcp excluded-address 192.168.1.1
Router(config)#ip dhcp excluded-address 192.168.1.250 192.168.1.255

To configure a DHCP Helper:

Router(config)#interface vlan 20
Router(config-if)#ip helper-address 192.168.20.10
Router(config-if)#end

To configure an interface for DHCP:

Router(config)#interface vlan 20
Router(config-if)#ip address dhcp
Router(config-if)#end

To configure DHCP Snooping (tells what ports can respond to DHCP Request):

Router(config)#ip dhcp snooping #enable globally
Router(config)#interface vlan 20 # for one specific vlan (most common)
# ip dhcp snooping trust - On specific interfaces

Show Commands:

show ip dhcp binding
show ip dhcp server statistics

Configure NTP:

# Server
R1#clock set 11:00:00 sept 4 2016
R1(config)#config t
R1(config)#ntp master # stratums are 1-15

Client:

R1(config)#config t
R1(config)#ntp server

To manually configure time (not NTP):

R2#config t
R2(config)#clock timezone CST -6 # tells the router -6 from GMT timezone
R2(config)#end
R2#clock set 12:40:00 20 10 2016

Show Commands:

show ntp associations
show ntp status
show ntp peers #maybe?

 

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