05-17-2009 07:07 AM - edited 03-06-2019 05:45 AM
Hi. If a port on a switch is not configured with a switchport mode access command and only with a switchport access vlan 10 for example, what exactly are the repercussions of this particular config on the port?
Thanks in advance.
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05-17-2009 09:53 AM
The Administrative mode will be set to 'dynamic desirable or dynamic auto' depending on the switch.
You can verify this status with the 'show interface fx/x switchport' command.
A dynamic desirable mode switchport will automatically trunk with another switch while a dynamic auto mode switchport will only trunk with another switch if this remote switch is set to dynamic desirable.
Setting the access-vlan without entering the 'mode access' will associate that port to such vlan when the switchport negotiates an access mode. If you connect to another switch, a trunk will be made, based on the requirements explained above, and the trunk native vlan will be used which by default is Vlan 1.
So in short, avoiding the 'mode access' can potentially create connectivity issues as you are leaving the switch to negotiate some important parameters.
HTH,
__
Edison.
05-17-2009 08:33 AM
It might possibly treat it as a trunk port allowing only VLAN 10, just a guess though, firing up a switch now to see...but I did research this question.....
From:
http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a008015bfd6.shtml
"Note: If the output of the show interface
05-17-2009 09:14 AM
Hi. Thanks for your response. I also checked a live switch and discovered that it is not defaulted to a trunk port when i ran the sh int trunk command. I think it in fact defaults to an access port.
05-17-2009 09:35 AM
You can also set it to trunking, then set it sw ac vl xx (10 in this case) and it will show as a trunk port, but also as a access port for vl 10...weird.
S1(config-if)#sw mo tr
S1(config-if)#sw ac vl 10
S1(config-if)#do sh int fa0/3 sw
Name: Fa0/3
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: down
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 10 (VLAN0010)
05-17-2009 10:18 AM
Yes it is weird. But i think since it is a trunk then it should forward all vlans by default. So i guess the trunk characteristic of the port supersedes the access mode function since a trunk is like a multi-access port.
05-17-2009 09:53 AM
The Administrative mode will be set to 'dynamic desirable or dynamic auto' depending on the switch.
You can verify this status with the 'show interface fx/x switchport' command.
A dynamic desirable mode switchport will automatically trunk with another switch while a dynamic auto mode switchport will only trunk with another switch if this remote switch is set to dynamic desirable.
Setting the access-vlan without entering the 'mode access' will associate that port to such vlan when the switchport negotiates an access mode. If you connect to another switch, a trunk will be made, based on the requirements explained above, and the trunk native vlan will be used which by default is Vlan 1.
So in short, avoiding the 'mode access' can potentially create connectivity issues as you are leaving the switch to negotiate some important parameters.
HTH,
__
Edison.
05-17-2009 09:57 AM
Excellent explanation, .... thank you.
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