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IP Phone needs to receive information from the correct DHCP server

Posted on 2011-09-25
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Last Modified: 2012-05-12
In our office, we currently have 4 CISCO Catalyst 500 switches. We added a new CISCO Small Business SFE2000P switch to the network.
The problem that i am having is that the IP phones that were placed on the CISCO Small Business SFE2000P switch are receiving the wrong network information. All IP phones in our network, connected to the CISCO Catalyst 500  switches, receive information from the DHCP server 192.168.102.1, which is correct.
When i remove the IP phones and place them on the CISCO Small Business SFE2000P switch, they are receiving IP information from the DHCP server 192.168.2.1.
To conclude when i add an IP phone to the existing switches, IP ris eceived from DHCP server 192.168.102.1. which is correct.
When i add an IP phone to the new added switch, IP is received from DHCP server 192.168.2.1. This is not what i want.
Looking forward to the feedback.  
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Question by:nat232ser
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by:Syed_M_Usman
ID: 36594960
do you have VLANs? in your office, logon to new switch using console and check switch configration.
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by:nat232ser
ID: 36596145
I do have VLANS. On the new added switch the VLANS were not updated. For some reason the VLANS are not updated to the new switch. What type of configuration should i look at?
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by:nat232ser
ID: 36597542
On our CISCO router, we have 2 DHCP Pool ranges. The following are:

DHCP Pool range: 192.168.102.11-192.168.102.254
Default router IP address: 192.168.102.1
For CISCO voice

                                   and

DHCP Pool range: 192.168.2.180-192.168.2.200
Default router IP address: 192.168.2.1
For PCs.

I have moved a certain amount of IP phones to the new added switch and the IP phones are receiving network configuration from the wrong DHCP pool. These IP phones are receiving network information from the DHCP Pool range that is being used for PCs. I need these IP phones to receive network information from the DHCP pool for CISCO voice. Any help please?
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by:Syed_M_Usman
ID: 36597669
you need to add switch ports of new switches to voice VLANS, logon to switch member switch of vtp domain and add switch ports to voice and enable DHCP helper...

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by:nat232ser
ID: 36597932
Do you want me to log on to a switch that is a member of a VTP domain?As i said before the IP phones on the old switches are working fine. Where do i enable DHCP helper?
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by:Syed_M_Usman
ID: 36597969
Sorry for not clerifying you earlier but please do as follows

Logon to NEW switch, as console
join switch with VTP Domain
Associate one port to voice VLAN
connect one ip phone with port, test if scucced ok othereise enable IP helper on switch port.
test and let me know what happeneds,
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by:nat232ser
ID: 36598065
The new switch is a Cisco Small Business SFE2000P. I am currently looking at this issue, but are you familiar with this switch to the point of VTP Domain. I am not able to find in the switch the VLAN Trunking Protocol. I am accessing the switch through a web interface.
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by:Syed_M_Usman
ID: 36598086
i dont have Cisco Small Business SFE2000P in my LAB. but dont you find any Console port behind your switch...can you post your switches configration (both working and non working)?
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by:nat232ser
ID: 36598253
VLAN ManagementI logged in to the switch via console, using serial cable. I was not able to see an option for VTP. The console does not allow us to input switch commands. The switch is in standalone mode. Could this be the reason why i am having problems with VLAN, because the switch is in Standalone mode and not Stack mode.
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by:Syed_M_Usman
ID: 36598297
My dear this is Cisco-Linksys switch.
i am sorry to say but ai m not expert for this....
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by:vivigatt
ID: 36599000
It should as simple as:
- Disable all DHCP service on "new" switch and on the subnet/VLAN in which are your IP Phones
- On the new switch, configure an ip-helper address for the subnet/VLAN in which are your IP Phones and make it pointing to the desired DHCP server IP address. If said DHCP server IP address has a pool for the subnet in which are your IP Phones, it should work OK.
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by:vivigatt
ID: 36599031
(in order for my suggestion to work, you may need to, either:
-  create another VLAN for the IP Phones on the new switch.
or
- make the IP-Phone ports on the new switch subscribing to the IP-Phone VLAN and connect one port of the new switch to another port in the IPPhones  VLAN in your infrastructure (on another switch), and assign said port of the new switch to the IPPhone vlan. You may also have to configure VLAN routing on the switches
I am not sure you even need to create a VLAN trunk if the routing is done on another switch
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deepdraw earned 500 total points
ID: 36600911
This is easy.
Dont plug the phones into the linksys switch.
If you have to, move one of the other cisco switches.
Or buy another cisco switch.

Greg
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by:nat232ser
ID: 36602036
Question for user viviqatt. The new switch is a CISCO Small Business SFE2000P. The configuration that you mentioned, can this be applied to the Small Business switch.
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by:vivigatt
ID: 36602452
I don't know this switch per se. But the configuration I propose is very basic.
The simpler would be:
- create a VLAN on the CISCO Small Business SFE2000P for the IPPhones. Let's say that this VLAN is named VLAN103 and uses this subnet:
192.168.103.0/24
(If there are only IP Phones connected to this switch, you may just assign this switch the IP address 192.168.103.1. The default VLAN for this switch would then be for subnet 192.168.103.0/24)
- connect all your phones to ports that are assigned to vlan103
- on your main cisco switch, also create this very same VLAN
- Enable the VLAN routing on the main cisco switch. You will need to create a "virtual IP address/interface" for VLAN103 on the main cisco switch. Let's say that this IP address is 192.168.193.254. This will be the gateway for devices connected to VLAN103
- assign ONE port of the main Cisco switch to VLAN103
- connect a cable between a port assigned to VLAN103 on the CISCO Small Business SFE2000P and the port assigned to the same VLAN on the main cisco switch
- On the may cisco switch, create an ip-helper for DHCP broadcast packets coming from VLAN103 so that these packets are redirected to the dhcp server
- On the dhcp server, create a scope and pool for the range 192.168.103.10-192.168.103.240 (keep the low and high IP adresses for potential static IP you may be needing). Configure the dhcp options for this scope. Note that the default gateway should be the IP address of the virtual interface for VLAN103 on the main cisco switch, which was 192.168.103.254 in my example.

Note that all the IP traffic between your IPPhones and devices that are not on teh same switch will be routed by the main cisco switch and will use the cable between the main cisco switch and the other switch.


Now, after having written all this, it seems to me that maybe the best would be to configure the SFE2000P so that it is connected to the main cisco switch to a port assigned to your regular VLAN for IP-Phones. This would be similar to replacing an existing IP phone by a switch on which you connect more IP phones. I would try my later suggestion first.
In short:
- Connect the SFE2000P to the Catalyst 500 using a cable plugged to a port on the catalyst 500 that was previously used by an IP phone.

HTH

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Author Comment

by:nat232ser
ID: 36709468
This question is for vivigatt.
IP Phones and PCs are connected  on each port. Does the configuration you mention still applies?
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Author Comment

by:nat232ser
ID: 36815068
There are two DHCP servers on the CISCO router. One is being use for IP Phones and the other for PCs. Can i create an IP helper on the router for interface being used in IP phones. The ip helper's ip address will be the ip address being used for the Small Business switch.
As i mentioned beore, the ip phones on the Small Business switch receive ip information from the DHCP server for PCs located in the router.
I also enabled DHCP relay on the Small Business switch. Will this work?
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by:deepdraw
ID: 36817605
If i get you right you are saying the phone is plugged into the switch and the pc is plugged into the phone.
You are not able to use the CISCO Small Business SFE2000P in this case.

Greg
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by:deepdraw
ID: 36817708
https://supportforums.cisco.com/thread/2023333
Someone else has put the question on a cisco forum and got the same answer.

 Also, you know the issue with support that you have implementing this is that the 2811 is a TAC supported switch and the SFE is a Small Business Support Switch so you will have two support resources to contact here to troubleshoot.  This is one of the reasons we typically try to steer partners away from this type of "hybrid" solution.

im sure it is possible but not something which you want to support in the future, or something you would want to pass to the next person who comes along..

Greg
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by:vivigatt
ID: 36818253
deepdraw question needs to be answered:
Is the phone plugged into the switch and the pc plugged into the phone ?
If so, I think that you will not prevent suing 2 separate VLANs. The VLAN for the phone will need to have some IP helper (or DHCP relay if you prefer, but they are really the same) that will forward DHCP requests FROM THE PHONES (ie from the Phones VLAN/SubNet) to the appropriate DHCP server.
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Author Comment

by:nat232ser
ID: 36890667
That is correct. The IP phones are connected to the switch and PCs are connected to the IP phone.
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by:nat232ser
ID: 36891226
Already on the CISCO router 2821 we have two DHCP pools. The following pools are:
IP phone DHCP pool:
Interface GigabitEthernet0/0.102
DHCP pool range - 192.168.102.11 - 192.168.102.254
Default router IP address 192.168.102.1
VLAN ID 102
IPaddress/subnet mask 192.168.102.1/255.255.255.0

PC DHCP pool:
Interface GigabitEthernet0/0.2
DHCP pool range - 192.168.2.180 - 192.168.2.200
Default router IP address 192.168.2.1
VLAN ID 2 (NATIVE)
IP address/subnet mask 192.168.2.1/255.255.255.0

Problem that i am having with IP phones receiving wrong DHCP pool is on the CISCO Small Business switch with IP address of 192.168.2.222/24.
How do i configure the ip helper on VLAN102? Do i configure this on the router?
Can i use the following commands:
interface vlan 102
ip address 192.168.102.1 255.255.255.0
ip helper-address 192.168.2.222

IP address 192.168.102.1, being the default router ip address for VLAN 102 [ip phones].
IP address192.168.2.222, being the Small Business switch IP address.
Can someone tell me if i am on the right track? Looking forward to hearing from you.
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Author Comment

by:nat232ser
ID: 36908743
I have IP phones connected to the Small Business SFE2000P switch, but they are getting IP addresses from a different dhcp scope. On the CISCO router i have configured two different scopes. Do i use IP helper-address in this case? How do i configure this?
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by:vivigatt
ID: 36909325
Since your phones are acting as "mini switches" for the PCs connected to them, the configuration is somewhat complex.
You need tagged VLANS for sure, and the port ON THE PHONE that is used to connect the PC MUST be tagged with the PC VLAN. The Phone itself MUST be tagged with the Phone VLAN. ANd the port on the SFE2000P that is used to connect the phone and thus the PC MUST be tagged with both VLANs. Then you must set different IP helpers ON THE SFE2000P for your 2 VLANs.

I am not sure this is doable. Tagging teh Phone and PC VLans IN THE PHONE is certainly doable. But setting trunked VLANS on the SFE2000P or different ipheleprs for different VLANs, this I don't know.

Consider it this way:
What is connected to the SFE2000P is a 2-port switch, on which is connected a phone and a PC. You will have a better understanding of your network topology then... You will, in particular, understand that the wire connected to the SFE2000P will be used for Phone AND PC traffic. And then, there must be a way to differentiate that traffic...
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by:nat232ser
ID: 36914879
For my testing i am using just an IP phone on one of the ports of the SFE2000P switch. The IP phone still receives an ip address from the DHCP scope that is being used for PCs.
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by:vivigatt
ID: 36916848
Yes, this is certainly expected, since ALL what is connected to your SFE2000P seems to send DHCP requests to your DHCP server for PCs.
If you configure the iphelper/dhcp relay on the SFE2000P to use the DHCP for your IP phone, the phone should then get an IP address in the correct scope. But not the PCs connected to the phone, of course...
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by:vivigatt
ID: 36949050
Weird way to retribute time and effort....

This solution that I provided before:
"make the IP-Phone ports on the new switch subscribing to the IP-Phone VLAN and connect one port of the new switch to another port in the IPPhones  VLAN in your infrastructure (on another switch), and assign said port of the new switch to the IPPhone vlan. You may also have to configure VLAN routing on the switches
I am not sure you even need to create a VLAN trunk if the routing is done on another switch"
is somewhat similar to what was accepted
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Expert Comment

by:restech2
ID: 37552214
The problem is that those model switches do not support CDP, and as a result you cannot configure a voice vlan. Cisco phones learn about the voice vlan though CDP, and by default do not have a specific vlan configured. As a result, they send their traffic untagged which is why they are pulling IP addresses on the data vlan. Your only option is to manually configure the phones that are connected to the SFE2000P series switch for the correct vlan. It is a time consuming process, and you would be best served by replacing the switch outright with an ESW-500 if you're budget conscience or a Catalyst ideally. Also, you'll have to configure each port as either General or a Trunk port, then specify that whatever your voice vlan traffic is will be tagged coming across the trunk, while the data vlan will not be.
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