Hi Rob,

So do I place all the ports on the 2940 switch the phone is connected to in trunk mode?

I have an asa with 2 vlan interfaces assigned on the inside (physical interface e0/5) connected to a 2940 switch which has a 7941 voip phone plugged into a random port. I trunk to the ASA from the 2940 and do I also trunk the port from the 2940 to the phone and set up trunking on the phone?

Hi Gerard,

The switchport mode trunk method was the only way to go with "older" switches like the 3500XL, but on all newer versions (like the 2960/2970/3750)the need for Switchport mode Trunk is not necessary..

I do know that it is unnecessary to configure the switchport in Trunk mode because when you use the Voice VLAN (with a native vlan) command a "special" dot1q trunk is automatically setup. The reasons I have seen to support this setup are many and vary from minimizing Trunking overhead to ease of configuration and everything in between :)

Here is one of the better threads I have ever read on this issue (with some Tac links as well). There are some great answers from Mahesh,Paolo Sankar and others here.

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Unified Communications and Video&topic=IP Telephony&CommCmd=MB?cmd=pass_through&location=outline@^1@@.1ddd5905/14#selected_message

Configuring Voice VLANs

http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_9_ea1/configuration/guide/swvoip.html

Here is the first line of the SRND for Voice Design;

When you deploy voice, Cisco recommends that you enable two VLANs at the access layer: a native VLAN for data traffic and a voice VLAN under Cisco IOS or Auxiliary VLAN under CatOS for voice traffic.

Separate voice and data VLANs are recommended for the following reasons:

•Address space conservation and voice device protection from external networks

Private addressing of phones on the voice or auxiliary VLAN ensures address conservation and ensures that phones are not accessible directly via public networks. PCs and servers are typically addressed with publicly routed subnet addresses; however, voice endpoints should be addressed using RFC 1918 private subnet addresses.

•QoS trust boundary extension to voice devices

QoS trust boundaries can be extended to voice devices without extending these trust boundaries and, in turn, QoS features to PCs and other data devices.

•Protection from malicious network attacks

VLAN access control, 802.1Q, and 802.1p tagging can provide protection for voice devices from malicious internal and external network attacks such as worms, denial of service (DoS) attacks, and attempts by data devices to gain access to priority queues via packet tagging.

•Ease of management and configuration

Separate VLANs for voice and data devices at the access layer provide ease of management and simplified QoS configuration.

To provide high-quality voice and to take advantage of the full voice feature set, access layer switches should provide support for:

•802.1Q trunking and 802.1p for proper treatment of Layer 2 CoS packet marking on ports with phones connected

•Multiple egress queues to provide priority queuing of RTP voice packet streams

•The ability to classify or reclassify traffic and establish a network trust boundary

•Inline power capability (Although inline power capability is not mandatory, it is highly recommended for the access layer switches.)

•Layer 3 awareness and the ability to implement QoS access control lists (These features are required if you are using certain IP telephony endpoints, such as a PC running a softphone application, that cannot benefit from an extended trust boundary.)

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/5x/50nstrct_ps556_TSD_Products_Implementation_Design_Guide_Chapter.html#wp1043366

Hope this helps!

Rob