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DHCP IPV 4

illyrianwa74630
Beginner
Beginner

Hi everyone, 

 

I've been trying to run DHCP on a client (interface F0/1) from SW2 but it doesn't seem to work. 

network and excluded addresses configured

default router set 

 

I can ping from and to the router. I can pring from sw2  to the router as well (172.18.10.1 - VLAN 10) 

 

Attached, ROAS show run  and SW2 show run. 
the interfaces on SW2 are on switchport mode access at vlan 10 as well. 

 

Rebooted, deleted dhcp settings, put them back again... I don't know what other solution to use here. 

 

 

Can anybody give a hint here please ? 

 

Thank you very much. 

 

 

1 ACCEPTED SOLUTION

Accepted Solutions

Hi again @Richard Burts

 

Just saw your response. 

 

I would have loved to wait to see the root of the problem, but due to professional deadlines linked to the issue, I couldn't further investigate, so I went for a "quick workaround" 

 

 

So, here's how I solved it: 

 

If it can help anybody:

 

- removing the DHCP Pools in the ROAS and re-configuring them from the beginning.  (Rather radical but efficient). 

 

Thanks a lot for your insights!

View solution in original post

6 REPLIES 6

Richard Burts
Hall of Fame Guru Hall of Fame Guru
Hall of Fame Guru

I have looked briefly at the posted config. I see one thing that should not be in the config. Remove this line

ip dhcp excluded-address 172.17.5.1 255.255.0.0

Make the change and let us know if the behavior changes. If there is still a problem then please post new copies of current configs and we will take a closer look.

 

HTH

Rick

Hello @Richard Burts 

Thanks for the reply.

I had already deleted that line indeed after i posted the config to the
cisco community but the behavior didn't change.

Connecting the host directly to the root bridge (S1) - which is the
neighbour device to the router :  there it works fine to a switchport in
access mode.

 

Also, I put the router in monitor mode (via terminal monitor) and I see a DHCPDISCOVER coming in... and then nothing. 

- Checked vlans and interfaces in S1, S2, S3 - to me everything looks OK, trunks are created, switchports look fine to me. 

- I removed the wrong range to the excluded address and left just the
addresses of the switches for the respective vlans.


-  Could the Portfast create issues due to "abrupt" frame forwarding? 

 

(I'm  pretty new to cisco and networks in general, sorry if my descriptions are not totally sound). 

 

 

It is highly unlikely that portfast is creating issues. Till we do know what the issue is we can't say for sure, but I will be amazed if it turns out to be portfast.

 

Can you provide some more information to help us understand the issue:

- identify a specific switch port which has a host connected that does not get a DHCP address.

- the output of show cdp neighbor from the switch

- the output of show vlan from the switch.

- the output of show interface status from the switch.

- the output of show interface trunk from the switch.

HTH

Rick

Hi again @Richard Burts

 

Just saw your response. 

 

I would have loved to wait to see the root of the problem, but due to professional deadlines linked to the issue, I couldn't further investigate, so I went for a "quick workaround" 

 

 

So, here's how I solved it: 

 

If it can help anybody:

 

- removing the DHCP Pools in the ROAS and re-configuring them from the beginning.  (Rather radical but efficient). 

 

Thanks a lot for your insights!

Thanks for the update. Glad to know that you found a solution. +5 for sharing the solution with the community. This community is an excellent place to ask questions and to learn about networking. I hope to see you continue to be active in the community.

HTH

Rick

Thank you Rick.

I appreciate it.

It's my 2nd month of training to the path of getting my CCNA, hopefully.

I'm sure i will be back with more questions in the future. If I can, I will
do my best to help!

Cheers!

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