DHCP issue when two identical Cisco IP Phones need to address different CUCM clusters

[NICNGUYEN]

Hi Team,

We use 7942G IP Phonesets in a UCCE call center environment on VLAN ID 300. Now we are planning to deploy other 7942G IP Phonesets for an administrative use to be connected onto a different CUCM cluster on the same VLAN.

What are the possible DHCP solution to make sure, when booting the 7942G IP Phone dedicated to the contact Center that it will not register on the "administrative" CUCM cluster and the other way around ?

Thanks & Regards

Nick

[Andrey Chertolyas]

You can just add their mac-addresses into the list of leases on your dhcp server to implement a strict accordance mac-ip and correct option 150.

Kind regards,
Andrew C.

[tonyperla]

This can all be handled by what you have set for the Option 150 within your DHCP server for that site.  If the phones are going to be on different VLAN's and different subnets, then you can simply add the CM IP addresses you want to use for each specific phone within your Option 150 within you DHCP scope

[NICNGUYEN]

Hi Andrew,

Thank you for your quick answer. Your proposal would be nice with a small number of IP Phones.

However we are expecting to deploy several hundreds (not to say thousands) IP Phones, so this would mean that we would have to know in advance every MAC_IP address to be configured in the DHCP server.

Kind Regards

Nick

[tonyperla]

You do not have to do anything with the MAC addresses of the phones.  This can be handled by setting the Option 150, within the DHCP scope for each subnet.

[NICNGUYEN]

Hi Tony,

Unfortunately I cannot use a different VLAN in my company. My final though was to ask Cisco to issue a special firmware to modify the Vendor Class but this is indeed an exeptional procedure. However if you have any other thought on this matter I would greatly appreciate your input.

Kind Regards

Nick

[tonyperla]

The important question here is if they are going to be on different subnets.  In this situation I would make so they are on different subnets.  If not, you could also statically set the tftp server options on each of your phones in the UCCE environment.

[Andrey Chertolyas]

Hi Nicolas,

So you are going to deploy thousands of devices over one VLAN, is it correct? I afraid that you should rethink your approach to network design, if it is possible. According to SRND the number of phones in one vlan should not exceed 512 devices. Besides of large amount of broadcast traffic some arp-cache related problems may appear on your CUCM cluster in case of exceeding of this number.

Kind regards,
Andrew C.

[NICNGUYEN]

Hi Tony,

I beleive setting statistic TFTP server on the IP Phones is probably the best approach in my case

Thanks & Regards

Nick

[islam.kamal]

Hi

The best solution if you have many IP phones , you have to make a seperate TFTP . Please go back to SRND .

Thank you

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[mkchandak]

Ideally if you have many phones, you should use different subnets, using one submit for 2 different clusters is not a good idea.

One more thing that you can try here if the phones would be preconfigured on CUCM and Auto registration would be disabled:

- Configure Option 150 with IP address of TFTP Server on both clusters. With Auto registration disabled, the phone should try the 1st server, when it does not get the configuration, it should try the 2nd server which would provide the configuration and let the phones register.

Hope this helps.

P.S: I have not used this configuration and therefore not sure if this would work. This needs to be tested.

[islam.kamal]

Hi

You can integrate with AD which you can also enable DHCP & DNS with option 150 for your IP phones configurations and can help you to assign IP addresses for your IP phones and that will be assign VLAN ID to your selected IP phones . To make sure that your CUCM not allow DHCP , form CUCM servicabilty - disable service of DHCP monitor or make sure that you do not configure DHCP server on your CUCM by this way , your CUCM won't participate on the process of DHCP IP addresses.

Thank you

please rate all useful information

[Aman Soi]

Hi Nicolas,

Just refer this discussion.

https://supportforums.cisco.com/message/4041277#4041277

regds,

aman