DHCP Failed. APIPA is being used

[agedmush66]

I am having trouble with this lab, currently. I keep getting a "DHCP Failed. APIPA is being used" error when switching the IPv4 from static to DHCP in IP Configuration. My instructor advised that I needed to switch my original IP Routing configs, which I did, but I still keep hitting the same error. There was one point where I was able to pull an IP for PC2, but after reloading the routers and switches to troubleshoot, the error came back. I was able to ping all IPs from both routers, aside from RTR01 to 192.168.0.1. But, after the reload looks like RTR01 can only ping 10.66.2.0. Any advice and help would be appreciated! I've uploaded my commands, the topology .png and the 8.2.1 .pkt file. Thanks!

[M02@rt37 · Accepted solution]

Hello @agedmush66 

First, since DHCP server is configured on Router R1, you need to add dhcp relay on Router R0. Why ? because Routers drop broadcast! DHCP discover use Broadcast! Then when PC0 send a DHCP broadcast request to Swicth0, Switch0 forward this broadcast to Router R0... but R0 drop that packet! You need to "convert" broadcast to unicast from Router R0---> that the dhcp relay's role!

To do this, add on Router R0 sub-interfaces this commande:

Also, take care how you configure Switch's ports where PC are connected! Configure them only on access mode. Like this for PC0:

Trunk links between Switches or between Switch and Router is OK! You need them to transport VLANs. 

After these modifications, PC0 has got its IP by DHCP:

[agedmush66]

Thank you M02@rt37 ! I am making these adjustments now. If I am setting the helper address to 10.66.5.2 What is the point of the other helper address of 192.168.0.1?

Edit: Those two adjustments were the solution and now both are receiving IP addresses. Thank you!

[M02@rt37]

You're so welcome @agedmush66 

[David Ruess]

It may not apply in your lab since you might only have one DHCP server but you can have multiple Helper addresses that point to other DHCP servers. This is for redundancy. When the router receives a DHCP Discover from the client it will send that as a unicast to all configured/reachable helper addresses to get an IP address from a DHCP server. This is also partly the reason for the other message of Request. If you have 3 helper addresses configured to point to 3 DHCP servers then all 3 will OFFER the host an IP address. The PC will respond with a REQUEST sent to the DHCP server that offered it the IP address. The other DHCP servers dont issue an IP address because the Client didnt "Request" one form them after then sent the OFFER.

If the helper address of 192.168.0.1 configured on the interface doesnt point anywhere to to a DHCP server then it is useless. It will send the DHCP Discover to that IP address but nothing will respond if its not in fact a DHCP server.

Hope that helps

-David