Remote DHCP Server 1

DHCP plays a huge role in most IPv4 networks. In some cases, the server sits on the same subnet as the client, but in other cases, the DHCP server is remote. When it is remote, you need to configure the DHCP relay agent feature as well. Today’s lab: configure that centralized DHCP server, and make sure the remote clients can get a lease from that server.

Requirements

For this lab, configure R1 to act as the DHCP server for two remote subnets off routers R2 and R3 as shown in the figure. Specifically:

• Use a DHCP pool per Subnet (Names: One and Two)
• Configure the correct default gateway configuration; you decide on the correct values.
• Configure a DNS IP addresses of 172.30.3.8 and 172.30.3.9.
• Set the domain name for the network to example.com.
• Set the lease length to 1 day, 2 hours, and 3 minutes long.
• Prevent the server from assigning to clients the IP addresses used by the routers in those subnets.
• Assume all router interfaces shown in the lab are up, working and the appropriate interfaces have been configured with IP addresses (per the initial configuration).
• Assume all routing protocol configuration is correct between routers, so that all routers learn routes for all subnets

Figure 1: Remote DHCP Topology

Initial Configuration

Example 1, 2, 3, and 4 show the beginning configuration state of R1, R2, R3 and SW1.

Example 1: R1 Config

hostname R1
!
interface GigabitEthernet0/1
 ip address 172.30.3.1 255.255.255.0
 no shutdown
!
router rip
 version 2
 network 172.30.0.0

Example 2: R2 Config

hostname R2
!
interface GigabitEthernet0/1
 ip address 172.30.3.2 255.255.255.0
 no shutdown
!
interface GigabitEthernet0/2
 ip address 172.30.1.1 255.255.255.0
 no shutdown
!
router rip
 version 2
 network 172.30.0.0

Example 3: R3 Config

hostname R3
!
interface GigabitEthernet0/1
 ip address 172.30.3.3 255.255.255.0
 no shutdown
!
interface GigabitEthernet0/2
 ip address 172.30.2.1 255.255.255.0
 no shutdown
!
router rip
 version 2
 network 172.30.0.0

Example 4: SW1 Config

hostname SW1
!
interface GigabitEthernet0/1
 switchport mode access
!
interface GigabitEthernet0/2
 switchport mode access
!
interface GigabitEthernet0/3
 switchport mode access

Answer on Paper, or Maybe Test in Lab

Next, write your answer on paper. Or if you have some real gear or other tools, configure the lab using them.

To test your solution if you happen to try it with CML/VIRL or real gear, use something that will attempt to use DHCP to lease an IPv4 address. On hosts, you can set the host to use DHCP. For instance, on Windows OS’s, use commands like ipconfig /release (to release the lease) and ipconfig /renew (to attempt a new lease). On Linux, try sudo dhclient –r to release, and sudo dhclient to lease a new address.

Alternately, if you have Cisco switches to use, include a switch connected the G0/2 interfaces of both R2 and R3. Then you can make each switch use DHCP for its own management IP address. For example, if R2 is connected to a LAN switch, and the switch used VLAN 1 on all ports, you could configure the commands interface vlan 1 followed by ip address dhcp to make the switch attempt to lease an address to use for interface VLAN 1. The show interfaces vlan 1 command on the switch will then show if the switch obtained its address or not.

Do this Lab with Cisco’s CML (Formerly VIRL)

You can do these labs on paper and still get a lot out of the lab. As an extra help, we have added files for Cisco Modeling Lab – Personal (CML-P). CML-P replaces Cisco Virtual Internet Routing Lab (VIRL) software, in effect serving as VIRL Version 2.

Below, find two files: a file useful with CML-P and another useful with VIRL. (Note that the CML-P file has a .yaml filetype, while the older VIRL file has a VIRL filetype.) Once the file is loaded, CML-P or VIRL will create a lab topology similar to this lab’s topology, with the initial configuration shown in the lab as well.

This lab’s CML file!

This lab’s VIRL file!

The CML/virl topology matches this lab topology exactly. The host info does as well.

Host device info:

This table lists host information pre-configured in CML/VIRL, information that might not be required by the lab but may be useful to you.

Handy Host Commands:

To see PC IP address: ifconfig eth1

Ping example: ping -c 4 10.1.1.1

Trace example: tracepath 10.1.1.1

To connect to another node within the topology: telnet 10.1.1.1