new LAN with Voip, best practices, recommendations

Unanswered Question


We have to implement a new LAN infrastructure for our new premises and would like to split voice and data traffic and give a certain priority to the voice traffic, using VLAN's and QOS.  The LAN will host computers and IP phones, all servers are in a data center.

As I'm a VOIP newbie I've been reading quite some documentation but I am confused and hope someone can clear things up for me.  The amount of information to go through is quite a lot and I would take less time if I'm pointed to the right direction, examples or documentation.

This is the hardware we have:

-1 cisco asa 5505

-4 cisco catalyst 3560 switches / 24Port POE / 100Mbit

-2 cisco catalyst 3560 switches / 24 Port POE / 1000Mbit

-20 Cisco 7940 series IP phones

-20 Polycom IP phones

.  First of all, having an asa 5505 and 4 3560 switches with 100Mbit ports, what is the best way to interconnect the devices to have the best throughput?  I thought of trunking all VLAN's on 1 port on the asa 5505 and then connect the first switch using a regular ethernet port, afterwards use the SFP uplinks to connect the other switches, but should I connect the switches in a chain or not?

cisco asa 5505 > SW1-1000mbits > SW2-1000mbits > SW3-100mbits > SW4...   ??

                                                  > SW2-1000mbit > SW4

cisco asa 5505 > SW1-1000mbit                                                                        ??

                                                  > SW3-100mbit > SW5 > ...

other option?

.  Basically all switch ports should have both the inside and voice Vlan as we will use the ethernet port on the phone to connect our PC's.  I was reading that to accomplish this I would have to configure the data Vlan as the native Vlan so the packes remain untagged but on the ASA 5505 i wasn't able to do this.  Although the 5505 documentation explains how to do it I always get a "command not recognized" error marking the native word in the command.  Looking on the internet I found this statement.

This switch port cannot pass traffic until you assign at least one VLAN to it. Trunk ports do not support untagged packets; there is no native VLAN support, and the adaptive security appliance drops all packets that do not contain a tag specified in this command.


.  Are there special considerations when using a mix of cisco IP phones and non-cisco IP phones?

. Regarding QOS, i have to use the auto qos voip trust command to assure that switches trust incoming packets that were already labeled by QOS on other switches.  Should I do this on the asa firewall as well.

I hope I'm clear enough.  Meanwhile i'm going back to testing

Thanks in advance


I have this problem too.
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Am I right thinking that if I want to have the voice and data traffic separated using the asa 5505 as the IVR and the 3560 switches for the Vlan port configuration i should:

on the 3560 switches

use switchport voice vlan vlanID & switchport access option

on the 5505

use the switchport trunk native vlan vlanID & switchport trunk option



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