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New Member

Help understanding Trunk ports

Hi Guys,

Not sure if these forums are meant for noobie questions but i'm new to the cisco / networking side of things. Read a fair few discussions on trunk ports etc and what they are and how they work. and I understand they should be used when communicating traffic that is on more than one vlan across one port.

I had an issue by which one of our ports on a cisco switch was not working correctly. the port itself connected to a POE phone and then that phone connects to the desktop to give it , its network connection.

The port it was on was configured as below

 

interface FastEthernet0/1

switchport access vlan 149

switchport voice vlan 200

!

 

this isn't the exact port I've just copied it onto a dummy switch on packet tracer, so I initially thought that the issue would be it had not been set to switchport mode trunk as it was sending both data for vlan 149 and voice vlan 200, but this was no the case. my colleague who set the port up new this would work but didn't really know why.

 

Why is it that this port can send multiple vlan data without being configured as trunk port? does this not count if the data is set to a voice vlan and a normal data vlan?

 

(The issue was to do with vlan 149's config in the end) It just confused me that's all!

 

 

 

Also, just so I understand this all correctly. if say you had a switch, and

ports 1-3 were on vlan 10, and set to switch port mode access

port 4-7 were on vlan 20, and set to switchport mode trunk

 

would ports 4-7 receive all the broadcasts sent from ports 1-3 even though they are on different vlan simply because Trunk is specified as the mode? (I think I would, would just like it confirmed!)

 

thanks guys

 

Anthony

Everyone's tags (2)
1 ACCEPTED SOLUTION

Accepted Solutions
VIP Super Bronze

Hi,Why is it that this port

Hi,

Why is it that this port can send multiple vlan data without being configured as trunk port? does this not count if the data is set to a voice vlan and a normal data vlan?

Cisco calls this "multi-vlan access port". This is fancy name for trunk port.  So, it is a trunk port.

would ports 4-7 receive all the broadcasts sent from ports 1-3 even though they are on different vlan simply because Trunk is specified as the mode? (I think I would, would just like it confirmed!)

Correct.  In this case trunk means all vlans.

HTH

 

4 REPLIES
VIP Super Bronze

Hi,Why is it that this port

Hi,

Why is it that this port can send multiple vlan data without being configured as trunk port? does this not count if the data is set to a voice vlan and a normal data vlan?

Cisco calls this "multi-vlan access port". This is fancy name for trunk port.  So, it is a trunk port.

would ports 4-7 receive all the broadcasts sent from ports 1-3 even though they are on different vlan simply because Trunk is specified as the mode? (I think I would, would just like it confirmed!)

Correct.  In this case trunk means all vlans.

HTH

 

New Member

Thank you for the reply Reza

Thank you for the reply Reza

 

one last question, "multi-vlan access port"

is this something the switch depending on its model will automatically recognize and allow or is this enabled when both data and voice vlans are specified?

so how would i know looking at a port that this functionality would be active / available?

thanks for you help

Anthony

VIP Super Bronze

Anthony,Yes, I believe it

Anthony,

Yes, I believe it depends on the model of the switch but most newer POE switches support it.  I don't have a list of the switches that do support it and the once don't.  I think you just have to try it and see if you can enable it.

HTH

New Member

Thank you for your help

Thank you for your help Reza

much appreciated

Anthony

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