VOIP DHCP options

[Dan91]

We are migrating to a Meraki MX105.  It is up and running and is our current edge router although the L3 routing is currently on our C3850 L3 switches.  I would like to migrate the voice VLAN to the MX105.  My question is about the DHCP options.

I have option 42 for NTP and option 2 for time offset both working in the DHCP scopes on the Cisco C3850 switches.  I was able to get DHCP flowing from the MX but unsuccessful in getting the DHCP options 42 and 2 to work from the MX.

Any suggestions would be greatly appreciated!

[ww]

Make a packet capture on mx lan. And check the opstions are send in the dhcp  packets.

If they are send, compare the option details to the c3850 options 

[Dan91]

Thank you.  I will do that.

[DarrenOC]

Hi @Dan91 , what telephony solution are you using?

[Dan91]

@DarrenOC Polycom phones using Nextiva.

[DarrenOC]

So the IP phones are getting an IP address via DHCP but aren’t picking up any of the scope options.  

Did you remove the L3 interface off the 3850 whilst testing?  

Factory reset of the ip phone?  Maybe try clearing the ARP cache on the 3850 also?

[Dan91]

Yes.  When I had them getting DHCP from the MX, I was able to have a phone pick up DHCP.

So the IP phones are getting an IP address via DHCP but aren’t picking up any of the scope options.  
Yes, DHCP from the Meraki, though no options were handed out.

Did you remove the L3 interface off the 3850 whilst testing?  
Yes, had the L3 interface removed from the 3850.

Factory reset of the ip phone?  Maybe try clearing the ARP cache on the 3850 also?

Factory reset may be a good call.  This was about a month ago so I cannot recall if I did or not.

Time offset - option 2 was forcing an integer and NTP is forcing an IP address or maybe a hostname will work.  Not working on this at the moment but will review later when the opportunity arises.

[BlakeRichardson]

1. What version firmware are you running on the MX? 

2. This will seem really silly but did you remember to click save after entering the DHCP options? I know that seems like a have you turned it off and back on question but some Meraki dashboard pages are a bit confusing when it comes to saving changes. 

3. Can the client device reach the NTP server if you trying pinging it? 

[Dan91 · Accepted solution]

We have fully migrated over to the MX and have DHCP to the phones working.

for Time offset for Central we had to use the integer: -21600

And for NTP we used IP addresses pointing to Internet based NTP servers.