bad address issue on the cisco 3850

[Nusret]

Hello dears,

we have cisco ws-c3850-24s-s in the our network system. İ configured ip helper-address in the interface vlan because we want to scatter the IP from our DHCP server. After that i started to get Bad Address from our DHCP server. Is there any command that i should configure in the interface vlan or in the switch.

You can see our configure at the attachment.

Thanks for your support.

[Mark Malone]

Hi
is there an alert your receiving in logs ? , theres no issue with how you specified helper , its just to reach the dhcp server when its coming from a different subnet

is anything showing in logging in 3850

[Nusret]

Hello Mark,

There is no diffrent logg about that in 3850 switch. We just see it in the DHCP server, its coming every per a minute.

for example; Any MAC address is getting IP from DHCP server after that same mac address want to get another secondry IP from dhcp server and it getting secondry IP. After Dhcp server is saying decline IP for first IP.

You can see similar scenario for our Vlan table,

192.168.0.0/25 Vlan100

192.168.0.128/25 Vlan200

int vla100

ip address 192.168.0.1 255.255.255.0

ip helper-address 192.168.168.5

int vlan200

ip address 192.168.0.129 255.255.255.0

ip helper-address 192.168.168.5

What can i do by our switch about that ? 

Thanks

[Mark Malone]

Hi
Why do you think the issue is on the switch ?
all your telling the switch is to change broadcast to unicast at the vlan interface so it can reach the DHCP server

as a quick test you could add a dhcp pool to the 3850 and see if the same issue exists when its local , if its not it may point to an issue with the server setup, i think something
might be wrong on the setup on server side , the switch plays no part in how the clients request the info or recieve it , its in the middle and just making sure the info reachs the DHCP server which it has done

have you tried to wirehsark any of the clients either to see whats going on at the DHCP request and discover stages

[Richard Burts]

I note that you tell us that these subnets are /25. But that is not what is configured on the interface.

int vla100

ip address 192.168.0.1 255.255.255.0

I do not know if the inconsistency is significant.

Are you sure that the pools are correctly configured on the DHCP server?

HTH

Rick

[Nusret]

hi,

First of all, thanks for your replies.

Actually i am not sure where is the problem i mean switch or server. I have any command that i missed, just that i'm looking for. Yeah maybe something wrong on the setup on server side. I will test it with dhcp pool to the 3850. Thank you again

Have a good day.

[Richard Burts]

Since the error messages are generated on the server I would guess that the issue is on the server.

HTH

Rick

[Nusret]

Hi Richard,

I thought that i could do something on the switch about that.. so i opened this case but you're right, i will talk with server side, again..

Thanks for cooperation

[Richard Burts]

Thanks for the update. Please do let us know if you make progress in resolving this issue.

HTH

Rick

[gwinn.joe]

It looks like your helper-address configurations are correct.  I've had this issue myself, it turned out to be the pool configuration on the DHCP server.  The DHCP pool was configured with the wrong default gateway and DNS addresses.  Check the pools on the DHCP server