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General vs Trunk Mode

Having recently had a run in with General and Trunk modes on an SG500X I was looking for the difference between General and Trunk modes and found this explanation:

  • General mode allows multiple untagged vlans and also multiple  tagged vlans to exist on the same switch interface.
  • Trunk mode allows ONE untagged vlan and multiple Tagged vlans to exist on the same switch interface.
  • Access mode allows only one untagged vlan to exist on a switch interface.

What I don't understand is how on earth does the swtich tell multiple untagged VLANs apart in General mode???

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General vs Trunk Mode

Hi, My name is Eric Moyers. I am a Network Support Engineer in the Cisco Small Business Support Center. Thank you for using the Cisco Community Post Forums.

I am not a switch guru by any means but the best that I remember is:

The native VLAN still applies to the General mode.  While it is possible to have multiple untagged vlans on a General port, you can only have ONE (1) PVID.  The PVID represents the native VLAN.

Untagged traffic may be sent via several untagged VLANs, returning untagged traffic will only be received by the PVID and therefore will NOT be forwarded to a specific VLAN.

I hope I remember correctly

Thanks

Eric Moyers    .:|:.:|:.

Cisco Small Business US STAC Advanced Support Engineer

CCNA, CCNA-Wireless

866-606-1866

Mon - Fri 09:00 - 18:00 (UTC - 05:00)

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General vs Trunk Mode

Hi, to add to Eric's post which is accurate, a trunk port will have an implicit ingress filter that cannot be disabled. A general port may have the ingress filter disabled making it a more true 802.1q operation.

General mode ports have a tendancy to work better when interoperating with non-small business products and 3rd party vendors due to the flexibility in configuration options, namely you don't have to specify a tagged default vlan, you may disable the ingress filtering.   Unlike a trunk mode, there is a special command set to tag the default vlan (no untagged members) where as general mode the command syntax is normalized like any other vlan.

-Tom
Please mark answered for helpful posts

-Tom Please mark answered for helpful posts http://blogs.cisco.com/smallbusiness/
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