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IP ROUTING and TRUNK ports

Posted on 2013-01-12
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In the case where I have 2 layer3 switches connected with only one cable.
I configure both connecting ports with "No Switchport".
Switch1 and Switch2 have different vlans configured and Vlan interfaces configured.
Now, do I still need a Trunk port between both switches in order to allow all vlans from both switches to talk to each other, OR the port that has been configured as "No Switchport" will be enough to do the job.

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Question by:jskfan
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by:Don Johnston
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Since the switches have different VLANs, there is no need for a trunk. Is this case you would create a routed link (no switchport) between the two switches.
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by:jskfan
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I said different..right but not completly different:

SW1 has Vlan10,20,30,40
SW2 has Vlan30,40,60,70
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by:Don Johnston
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Nice try. But until you apply the qualifier, different is an absolute. :-)

If there are ANY (see what I did there?) VLANs which are common to both switches, you will need a trunk.

Since VLANs 30 and 40 are common, you'll need a trunk.

Now because were obviously a jailhouse lawyer in a previous life, I'll add this: Just because the VLAN numbers are the same, doesn't mean that they are common. Granted, it would be extremely bad practice, but it could be. So I'll qualify my statement to be:

If there are any VLANs (that represent the same IP network) which are common to both switches, you will need a trunk.

How's that? ;-)
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by:jskfan
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there is "No Switchport Trunk " command too. what would this do ?
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That's only the first part of a command.

"no switchport trunk native vlan" would remove the native vlan configuration of a trunk. Which would return the native VLAN to the default.

You can also remove encapsulation commands (dot1q, isl) and other parameters. Or you could simply set them to whatever value you want. "switchport trunk native vlan 1" for example would do the same thing as "no switchport trunk native vlan".
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