DHCP SERVER REACHABILITY


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SCENARIO

(NETWORK DEVICE) : ROUTER ========= DHCP SERVER : (DHCP DEVICE)

Here, Router is communicating with DHCP server, so that Host connected to the router Can get the IP from the DHCP scope defined on the server

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 What is the configuration required on the Router?

IP Helper address has to be defined on Router, which belongs to the DHCP server

 

Example:

interface GigabitEthernet0/1.174

description Voice VLAN

encapsulation dot1Q 174

ip address 10.144.174.1 255.255.255.0

ip helper-address 10.144.3.72

ip helper-address 10.146.3.101

 

Here, Points to be noted are:

Router has a sub-interface Gi0/1.174.

VLAN assigned to this sub-interface is 10.144.174.0/24

This VLAN is assigned to hosts

These hosts want to get IP address from the IP range or DHCP scope defined on the DHCP server.

For above purpose, we need to define IP helper address (which belongs to DHCP server)

***************** 

How to confirm if VLAN or Subnet, related to the host is reachable till the DHCP server?

If VLAN of host is reachable till DHCP server, only then Hosts will be able to Get IP address from the IP range or DHCP scope defined on the DHCP server.

As we can see above, IP assigned to sub-interface is 10.144.174.1

IP Helper address is 10.144.3.72 and 10.146.3.101

 

There must be reachability between VLAN assigned to host and VLAN belonging to IP Helper address.

 

Example:

rtr#ping 10.144.3.72 so 10.144.174.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.144.3.72, timeout is 2 seconds:

Packet sent with a source address of 10.144.174.1

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 1/3/4 ms

 

rtr#ping 10.146.3.101 so 10.144.174.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.146.3.101, timeout is 2 seconds:

Packet sent with a source address of 10.144.174.1

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms

****************

 

Things are Fine from the Router side, Remaining part is DHCP server , which has to be checked. This needs different approach .. !!

 

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