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New Member

DHCP Issue on Cisco 2960

 

I have an device that use Multicast and is unable to aquire an ip address when connected to a 2960 switch. I have a 3560 switch that is configured with the DHCP scope. We have DHCP pool configured. layer 2, and layer 3 switch's.
 
Basically what’s happing  is that if we connect the device to the switch it does not get a DHCP address however if we apply a static address it works.  Now I have duplicated this in the lab and the everything works fine, the only difference is that I have a different IOS on my Lab switch.  The only thing i can think of is the IOS.

Any help would be appreciated.

The IOS on the 2960 is flash:c2960-lanbasek9-mz.122-55.SE7.

 

13 REPLIES

Hey,May you share the running

Hey,

May you share the running configs for both the ports on C2960, the uplink port and port where this machine is connected.

Regards,

RS

New Member

Hi Rajeevsh,I have attached

Hi Rajeevsh,

I have attached the configs for both switches. A bit more information on the device that i'm trying to connect. It communicates by multicast and the documentation states that multicast should be configured on both switches. 

New Member

HI Rajeevsh, Did you get a

HI Rajeevsh,

 

Did you get a chance to review the configurations. Somehow the device is ignoring  to a DHCP option,

 

Thanks,

Anil

Hi Anil,Configuration is

Hi Anil,

Configuration is simple enough and i dont see any reason why is shouldn't work.

However does other machines when connected to this 2960 gets an IP address from layer 3 switch?

Also please add show log from layer 3 switch for any clues.


Regards,
RS

New Member

HI Raj,Yes if i connect a

HI Raj,

Yes if i connect a Laptop to the 2960 layer 2 switch it is able to get a DHCP address from the layer 3 switch. One thing i forgot to mention is that the Device which uses multicast , it work's on the Layer 3 switch that is configured for Multicast and get a DHCP address.

Do you think i have to run multicast on the access layer switch. I understand that i will have to get a layer 3 switch that i capable of doing this.

We have other sites that have layer 3 switches and its work fine. So i'm thinking it may be a multicast issue.

What are you thoughts?,

Thanks,

Anil

Hi Anil,Whenever we connect a

Hi Anil,

Whenever we connect a machine to network it will first obtain IP address and later will start using any other protocol.

So i believe we need to understand how your this machine works as you mentioned that its working on other sites connected to layer 3 switch, also did you check the logs on layer 3 switch. Try enabling 'debug ip dhcp server packets' on layer 3 switch and check if we are even receiving dhcp request from that machine.

Regards,

RS

New Member

HI Rajeevsh,I enabled

HI Rajeevsh,

I enabled debugging on the switch and the output from the router is attached.I am getting the error:- DHCPD: there is no address pool for 10.25.246.247. Now this is the lan segment on Vlan 1.

I want the Device to pick up a dhcp address from Vlan 2.

Am i missing something in the config?

 

Hi Anil,

Hi Anil,

I need to know the mac-address of the client as i see two different DHCP Requests from:

0100.237d.14b5

and

0198.fe94.dcd6

 

Moreover i see only one DHCP pool on the layer 3 switch:

ip dhcp pool 
   network 10.65.117.0 255.255.255.0
   dns-server 198.6.1.122 198.6.1.142 8.8.8.8
   default-router 10.65.117.1

 

And as you said that it should pick IP address from vlan2, but i dont see any pool for vlan2 on the contrary you did mention that if you connect your laptop on that port it does pick IP address from vlan 2. its actually very weird.

If possible collect the wireshark captures from machine interface for more debugging. i want to see the DHCP process. and let me know if you need any help in collecting captures

 

Regards,

RS

New Member

HI rajeevsh,Yes there is only

HI rajeevsh,

Yes there is only one pool on the Layer 3 switch, should i configure  one on the layer 2 for testing purposes or layer 3 swich.

Also how would that pool look under Vlan 2. Also i have duplicated this scenario in the lab and the Diagnostic device picks up a DHCP address. I am having one of the Diagnostic device shipped back to me and i will test it there is a possibility its not configured correctly. Can you send me a config for Vlan 2 that i can apply,

 

Thanks,

Anil

New Member

HI Rajeevsh,I believe the

HI Rajeevsh,

I believe the Clients mac is 98fe.94dc.d6e8. I also see this on teh log on the Layer 3 switch.000415: Jun  5 16:21:07: DHCPD: Sending notification of DISCOVER:
000416: Jun  5 16:21:07:   DHCPD: htype 1 chaddr 98fe.94dc.d6e8 <--------------Device
000417: Jun  5 16:21:07:   DHCPD: interface = Vlan1
000418: Jun  5 16:21:07:   DHCPD: out_vlan_id 0
000419: Jun  5 16:21:07: DHCPD: there is no address pool for 10.25.246.247

Foe some reason it is not seeing the Pool. Could i use this command so that the Client is identified.

client-identifier  98fe.94dc.d6e8

 

New Member

Laptop 0100.237d.14b5

Laptop 0100.237d.14b5
0100.237d.14b5 Laptop

Client 0198.fe94.dcd6

Hi Anil,You may try adding

Hi Anil,

You may try adding the client-identifier command but i am not sure if it will work as there is no DHCP pool configured for 10.25.246.247 (i am hoping its from vlan2 subnet).

So i recommend following in given order:

1. Connect the laptop to same port and share the IP address details obtained via DHCP,

2. Add the client-identifier command ans check if its working,

3. Configure DHCP pool for vlan 2:

ip dhcp pool
   network 10.25.246.0 255.255.255.0
   dns-server 198.6.1.122 198.6.1.142 8.8.8.8
   default-router 10.25.246.1

you also need to create SVI for vlan 2 on layer 3 switch 10.25.246.1 along with its vlan.

Regards,

RS

New Member

HI Rajeevsh,Just an update

HI Rajeevsh,

Just an update for you, it turned out that there may have been an issue with the switch, there was a power issues at the site and the router failed, i don't know the specifics however they tried another router and everything worked. They are getting a new router so i will let you know if we have any issues with the new router. I appreciate all your assistance,

Thanks,

Anil

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