Ip helper-address (DHCP) Experiment

 

DHCP can only be used over Ethernet because of the mac address. Is there a way to assign an ip address to an Ethernet pc as a non-Ethernet link route? Dhcp is a broadcast and is isolated by routes. How can this problem be achieved?

Vro does not forward broadcasts. The help address helps the client establish a connection with the server by directly forwarding these broadcast packets to the target server. If the "ip helper-address" command is defined, the forwarding function is automatically enabled for eight default UDP ports: TFTP (69) and DNS (53), time (37), NETBIOS service (137), NETBIOS datagram Service (138), BOOTP server (67), BOOTP client (68) and the access control system TACACS (49 ).

Lab Topology

: R1 is a server and an ip address is allocated to r4.

 

If I set Automatic Acquisition on the e0/0 port of r4, dhcp will be sent to discover the broadcast, and the route will block this broadcast, what is the basis for this function? Ip helper-address takes effect. Set this configuration to e0/0 port of r3.

Post Configuration

R1:

Ip dhcp pool cisco

Network 3.3.3.0 255.255.255.0

!

Interface Ethernet0/0

No ip address

Shutdown

Half-duplex

!

Interface Ethernet0/1

No ip address

Shutdown

Half-duplex

!

Interface Ethernet0/2

No ip address

Shutdown

Half-duplex

!

Interface Ethernet0/3

No ip address

Shutdown

Half-duplex

!

Interface Serial1/0

No ip address

Shutdown

Serial restart-delay 0

!

Interface Serial1/1

No ip address

Shutdown

Serial restart-delay 0

!

Interface Serial1/2

Ip address 1.1.1.1 255.255.255.0

Serial restart-delay 0

!

Interface Serial1/3

No ip address

Shutdown

Serial restart-delay 0

!

Router VPN 1

Network 0.0.0.0

Auto-summary

 

R2:

Interface Serial1/2

Ip address 2.2.2.2 255.255.255.0

Serial restart-delay 0

!

Interface Serial1/3

Ip address 1.1.1.2 255.255.255.0

Serial restart-delay 0

!

Router VPN 1

Network 0.0.0.0

Auto-summary

 

R3:

Interface Ethernet0/0

Ip address 3.3.3.1 255.255.255.0

Ip helper-address 1.1.1.1

Half-duplex

!

Interface Serial1/3

Ip address 2.2.2.3 255.255.255.0

Serial restart-delay 0

!

Router VPN 1

Network 0.0.0.0

Auto-summary

Set ip add dhcp and no shutdown for e0/0 of r4.

Here, we need to pay attention to the reason why we need to set

Because ip helper-address must implement two conditions, the first one is to configure this command on the interface.

The second is that the server must know how to go to the client, so this configuration must be done.

After completing these configurations, dhcp is automatically assigned to the e0/0 port of r4.