problem with pc ip address on vlan 4

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Sep 7th, 2007
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we have a cisco network backbone, we have 2 stacked 3750 swithes one is a 24 port that is being used the other is 48port, that is only using Fast ethernet 0/1 prot, and there are polycom phones that each users desktop connects to via ethernet port on the phone. the issue is that a ip address is being distrubuted to the phone but not the desktops via dhcp , the vlans are setup via vlan 4 for data and vlan 5 for voice, i will attach the config of the 48 port if you need it, i can not pin point what exactly is going on

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Edison Ortiz Fri, 09/07/2007 - 17:04
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a) What Vlan is the DHCP server located ?

b) Do you have ip helper-address configured on Vlan4 if the DHCP server resides in another Vlan ?

c) Did you create a scope in the DHCP server to provide IPs for devices in Vlan 4 ?

d) If you plug the desktop directly onto the switchport, not via the phone, can they obtain an IP ?

jeff-adair Fri, 09/07/2007 - 19:41
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a) What Vlan is the DHCP server located ? how do i verify that?

b) Do you have ip helper-address configured on Vlan4 if the DHCP server resides in another Vlan ? same here how do i verify that

c) Did you create a scope in the DHCP server to provide IPs for devices in Vlan 4 ?same here how do i verify that

d) If you plug the desktop directly onto the switchport, not via the phone, can they obtain an IP same here how do i verify that


im sorry im a begining cisco guy

Richard Burts Sat, 09/08/2007 - 09:28
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Jeff


I do not want to be dismissive but many of these are quite simple questions. My responses are found in line.


a) What Vlan is the DHCP server located ? how do i verify that? Someone needs to know where the DHCP server is located. If you do not know then find someone who does know. If no one knows then you may need to put a sniffer or other packet capture device and examine traffic to find the address of the server in DHCP traffic on the network. Or you may want to consider hiring a good experienced consultant to come in and help to solve this.


b) Do you have ip helper-address configured on Vlan4 if the DHCP server resides in another Vlan ? same here how do i verify that You verify it by looking at the config of VLAN 4. Does it include the command ip helper-address or does it not include this command?


c) Did you create a scope in the DHCP server to provide IPs for devices in Vlan 4 ?same here how do i verify that Someone in the organization should have responsibility for the DHCP server. Find that person and ask them. If no one has that responsibility then you need to hire a good experienced consultant who can straighten this out for you.


d) If you plug the desktop directly onto the switchport, not via the phone, can they obtain an IP same here how do i verify that You take a PC from its current location and you take it near the switch. You then plug the Ethernet interface of the PC into an available port in the switch which is configured to be in VLAN 4. You verify that the PC is configured to learn an IP address by DHCP and then you boot the PC. You then check to see if the PC has an address assigned to its Ethernet interface that is in the expected subnet.


I would suggest that posting the configuration of the switch would allow us to gain a better understanding of what the situation is and perhaps to give you more helpful answers.


HTH


Rick

jeff-adair Mon, 09/10/2007 - 08:34
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here you go


this is the 2950 switch and the 3750 which is connected to the 2950:


see the attached files



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Richard Burts Mon, 09/10/2007 - 09:11
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Jeff


I have looked at the config files that you posted. Unfortunately the config from the 3750 is truncated and does not include the configuration of the VLAN interfaces for VLAN 4 and 5. So we can not tell yet what is set up for these VLANs (especially about DHCP).


I see that both the 2950 and the 3750 have access ports configured with data in VLAN 4 and Voice in VLAN 5. Can you clarify whether the problem is with phones and PCs connected to one switch or the other - or is it happening the same on both switches.


I notice that the 2950 ports have things like port security configured that the 3750 does not. I wonder if this plays some part in the problem?


I also notice that you are configuring voice vlan 5 to get support for data and voice. In looking at the documentation it is fairly specific that this feature was developed for Cisco phones. Are you sure that the polycom phones also support this feature? As an experiment I wonder what would happen if you took a couple of the ports where the problem is happening and configured the ports as trunk ports and made sure that VLAN 4 and 5 are included in the trunk.


HTH


Rick

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