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Cisco Switch 3750 port problem

Posted on 2014-03-30
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Last Modified: 2014-04-15
I have two ports on Cisco 3750 can't get DHCP IP addresses (only get self assigned IP), other ports with same config can get IP address without problem.

Could you please suggest anything I can do for troubleshooting? Thanks
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Question by:tonitoni99
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by:lruiz52
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Can you post the switches config?

Also make sure that the switch port is on the correct vlan and that it is not in shutdown.

Config t
              Int ?
                Switchport.  Access vlan ??
               No shutdown
                End

Writ
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by:tonitoni99
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by:Miftaul
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Please tell which two ports you are connecting the pc.
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by:lruiz52
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Yes, post which ports!
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by:Don Johnston
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Come on guys... There's only 192 ports. How hard could it be to guess?  ;-)

I'm going to guess that the host is on port g4/0/20. And that the absence of an IP helper command is causing the problem.  And that the DHCP server might not have a scope defined for that network.
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by:tonitoni99
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They are int1/0/35 and int1/0/36. thanks
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by:Don Johnston
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It's not the switch.

Maybe the DHCP pool is out of addresses.
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by:tonitoni99
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I checked there are still have 50% of the DHCP available, and new PC are still can get IPs. How to verify if it's DHCP issue? thanks
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by:Miftaul
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Setup up a pc with static ip within the dhcp subnet. Connect the pc on one of the two switchport and try pinging your dhcp server.

Do you get a reply, if not it could be a switch issue.
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by:tonitoni99
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I tried the suggestion from Miftaul, setup a PC with static IP, when plugin to these two problem ports, can't ping the dhcp server. If plug in other port, no problem.

Now the problem is with the ports, any idea how to resolve them? thanks
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by:Don Johnston
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Post the output of:
"show int status g1/0/34"
"show int status g1/0/35"
"show int status g1/0/36"
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by:Hassan Besher
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Try to configure Port Monitoring (SPAN) on port  int1/0/35 and destination port (whatever) is connecting to your wireshark station to see exactly what is going on

My_Switch(config)# monitor session 1 source interface 1/0/35 both
My_Switch(config)# monitor session 1 destination interface ......

A destination port has these characteristics:

•For a local SPAN session, the destination port must reside on the same switch stack as the source port. For an RSPAN session, it is located on the switch containing the RSPAN destination session. There is no destination port on a switch or switch stack running only an RSPAN source session.

•When a port is configured as a SPAN destination port, the configuration overwrites the original port configuration. When the SPAN destination configuration is removed, the port reverts to its previous configuration. If a configuration change is made to the port while it is acting as a SPAN destination port, the change does not take effect until the SPAN destination configuration had been removed.
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by:tonitoni99
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Port      Name               Status       Vlan       Duplex  Speed Type
Gi1/0/35  "User Port"        connected    3          a-full a-1000 10/100/1000BaseTX

Port      Name               Status       Vlan       Duplex  Speed Type
Gi1/0/36  "User Port"        notconnect   3           auto   auto 10/100/1000BaseTX


Port      Name               Status       Vlan       Duplex  Speed Type
Gi1/0/34  "User Port"        notconnect   3            auto   auto 10/100/1000BaseTX


If a PC connects into gi1/0/35, it said connected, however, it only has self assigned IP. I also find port 34 has the same problem.
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by:Don Johnston
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They are int1/0/35 and int1/0/36. thanks

I also find port 34 has the same problem.
So now port g1/0/34 has this problem also???

Is there a VLAN3 port that is working correctly?  If so, which one?
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by:tonitoni99
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yes. gi1/0/34 has problem as well, the rest of ports are fine, for example gi1/0/26.
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by:Don Johnston
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Please post the output of the following commands for a working port and a non-working port (with a device actually connnected).

show interface switchport
show interface
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by:tonitoni99
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problem port gi1/0/34 (non-working port)

sh int gi1/0/34 switchport
Name: Gi1/0/34
Switchport: Enabled
Administrative Mode: static access
Operational Mode: static access
Administrative Trunking Encapsulation: negotiate
Operational Trunking Encapsulation: native
Negotiation of Trunking: Off
Access Mode VLAN: 3 (VLAN0003)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: 101 (NEW-TEST-VOIP-VLAN)
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL

Protected: false
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Appliance trust: none

a working port

#sh int gi1/0/41 switchport
Name: Gi1/0/41
Switchport: Enabled
Administrative Mode: static access
Operational Mode: static access
Administrative Trunking Encapsulation: negotiate
Operational Trunking Encapsulation: native
Negotiation of Trunking: Off
Access Mode VLAN: 3 (VLAN0003)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: 101 (NEW-TEST-VOIP-VLAN)
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL

Protected: false
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Appliance trust: none
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by:tonitoni99
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any more suggestion? thanks
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by:Hassan Besher
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is DHCP Server connected to the same switch?

if not is there any security features applied like dhcp-snooping,... ?
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by:tonitoni99
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there is no dhcp-snooping features. any other idea? thanks
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Accepted Solution

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Hassan Besher earned 500 total points
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install wireshark at PC and configure it as dhcp client and see what is going on.

Connect dhcp server to the same switch, and test !
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