Cisco Switches and VOIP setup.

[skk391]

Hi,

Just looking for some background information on how to attack a network design of a VOIP implmentation.

At the moment we have configure a network where we have the following



Network A ----> Router -----> Switch -----> Phone ------> PC where the pc is attached to the phone.


At the moment the router is the DHCP router & the phones and the PC's are all on the same subnet. There are only going to be 20 phones and 20 pc so we are not to concerned with Voice & Data Vlans etc.

But if the number of the agents does increase then this type of network design may cause us issues.

But I cant get my head around how this will work so can anyone please give me some background on how this will work.

I have read that the you create 2 vlans - so one is the voice and the second is for the data.

How does the switch know what is the voip taffic and what is data. How do I configure the port on the switch which is connected to the phone.

I know how to configure the vlan... ie switchport mode access, switchport access vlan 10, but this access port will be carrying traffic from 2 vlans, so do I configure it to be a trunk and allow two vlan across it ?

How will the phones and the pc's get their ip addresses. I have configure DHCP on the router to assign ip to any device requesting an address but this is all within a single ip range how do I get the dhcp server to assign ip addresses on different ranges. Can I configure 2 dhcp server ranges on the router? How does it work?

you guys can probadly tell that I am getting rather confused so any help would be grafeful.

 

[unclerico]

it's no problem. you most definitely want to go down the road of splitting your voice and data so design it like that from the start.

as for how your phone and PC will know which VLAN is which and what device to contact for DHCP; it all depends on the phone. Some phones support CDP, some support LLDP-MED, some support both, and some support nothing. the phone and the switch will exchange CDP or LLDP-MED frames to determine what is the voice vlan (aux vlan) and what is the data vlan (untagged). if your phone supports CDP then your switch port configuration will be like this (partial config):

interface fastethernet0/0
  switchport mode access
  switchport access vlan 10 <--- data vlan
  switchport voice vlan 20 <--- voice vlan

if you use lldp-med you should define a network policy in global-config mode and then apply it to the interface(s). post back if you need to configure lldp-med.

for dhcp, you simply define two dhcp pools on the router.

I hate all Uppercase... I don't want my groups to seem angry at me all the time! =)
- ColdFlame (vbscript forum)

 

[VinceWhirlwind]

...and for non-CDP phones, it would be:
sw trunk dot1q
sw trunk native vlan 10
sw trunk allow vlan 10,20
sw mode trunk
spanning-tree portfast trunk

 

[skk391]

Thank you very much, vey good information, its pointed me in the right direction.

Thanks again.... May have some questions later for you though!

 

[ADB100]

...and for non-CDP phones, it would be:
sw trunk dot1q
sw trunk native vlan 10
sw trunk allow vlan 10,20
sw mode trunk
spanning-tree portfast trunk

You don't need to hard-code an interface as a trunk if the phone doesn't support CDP. Configure your interfaces as access ports with a voice VLAN as unclerico describes. In reality an access port with a voice VLAN is a trunk - its just a trunk with only one tagged VLAN. If you hard-code it as a 'proper' trunk then STP behaves differently and you can't enable all the 'nice' edge protection mechanisms you would normally want to on access ports that support a single edge device - or an IP Phone plus a single edge device.

Andy

 

[VinceWhirlwind]

I'm always open to more information about the practical operational differences between using "voice VLAN" and configuring the interface as a "proper trunk".
I haven't looked into this lately, but when I *was* looking into it, there were virtually no Cisco white papers detailing mixed-vendor operability except one paper I found which recommended the "proper trunk" setup in relation to (Polycom VC? Hazy memory) equipment.

I'd be interested in your perspective of how this changes how we use the 'nice' edge protection mechanisms?

My experience with non-Cisco was that the ports are setup as proper trunks with STP faststart/BPDU protection/rootguard/DHCP snooping/ARP inspection (whichever they asked for), so I've always thought to set it up the same when it isn't a Cisco/Cisco setup.

 

[ADB100]

In reality whether its an access port with a voice VLAN or a 'proper' trunk with a native VLAN and one tagged VLAN they are effectively the same from a forwarding of data point of view. If its an access port with CDP enabled then in the CDP updates the switch includes the 'Auxilliary VLAN' field advertising the Voice VLAN configured on the port.
I have just checked and you can enable most of the things on a hard-coded trunk that you can on an access port: stp portfast with the 'spanning-tree portfast trunk' command, BPDUGuard & BPDUFilter. This wasn't possible in some older IOS releases.

With a hard-coded trunk though you can't enable port-security or 802.1x which I think are pretty important 'edge guard' features.

HTH

Andy

 

[madwok]

Another method that I want to share:

If your IP does not do CDP/LLDP , you can also nudge it along by hardcoding the darn VLAN ID in its memory setting and set the switch port run on access / voice vlan as suggested above . Much less headache on remote sites where less sophisticated users could move IP phones with ease.

We've done this in Nortel, Avaya, NEC & Cisco phones without any ill effect at all on the network.

Thanks,

madwok

 

[ADB100]

If your IP does not do CDP/LLDP , you can also nudge it along by hardcoding the darn VLAN ID in its memory setting and set the switch port run on access / voice vlan as suggested above . Much less headache on remote sites where less sophisticated users could move IP phones with ease.

We've done this in Nortel, Avaya, NEC & Cisco phones without any ill effect at all on the network.

Yes, a valid method for getting the voice vlan into the phones. However, if you have anything more than a few phones to rollout then it takes time, plus if you want to change the voice vlan number then you need to manually reconfigure all the phones...

OK for testing but not for a real environment.

Andy

 

[VinceWhirlwind]

Agreed, although it's amazing how many phone people are happy to spend hours manually configuring phones rather than just setup DHCP or LLDP/CDP.

 

[ADB100]

'Network Provisioning'....

 

[madwok]

Ever register a Cisco phones on CME ? Yes , pain in the tail with them MAC address but there is always some manual requiring in the phone world .At least for now we can let all the data guys do all the wiring /PC installation and the phone guy just piggy back to the data jack . No more crawling behind them monster credenza to look for the puny RJ21 . Time saving right there