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Etherchannel problems in Packet Tracer

Posted on 2011-02-15
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Last Modified: 2012-06-22
I am working on setting up Etherchannel for multiple switches.  There are some problems and things do not seems to be functioning properly.  I have attached a Packet Tracer file for analysis.  Rename it Etherchannel.pkt as I had to rename the extension to upload.  Here are my questions:

1. Anything wrong with this design?
2. Why is every switch it's own root bridge for VLAN 1?  Is this normal for Etherchannel?
3. I can ping from 10.0.0.8 in VLAN 100 to 10.0.0.3, but the ping time is much higher than I would expect.  What would cause this?
4. I can't ping from 10.0.0.5 in VLAN 200 to 10.0.0.2.  What is stopping this?
 Etherchannel.zip
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Question by:B1izzard
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Expert Comment

by:Don Johnston
ID: 34902220
1. If it works, it's a good design. Could it be different? Sure. But without knowing the design goals, it's hard to say.

2. Because VLAN 1 isn't allowed over the interswitch links. So from the perspective of VLAN 1 on each switch, there are no other switches. If you add VLAN1 to all the trunks, then you'll see a single root.

3. Packet Tracer is not real. It's a simulation. I wouldn't worry about that.

4. For one thing, VLAN 200 doesn't exist on switch 0. There could be other reasons beyond that.
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Author Comment

by:B1izzard
ID: 34902476
Awesome.  Thanks for the great answers.

The design goals are for an actual project that I am working on in which we are trying to setup redundancy between 2 sites via a fiber optic multiplexer.   Channel-group 2 is essentially the fiber trunks between the sites.  The problem that I have been having is that some VLANs work and some don't...but that is another question.  

The reason the one link isn't in a channel-group was only because Packet Tracer only allows 6 channels, and that would have been channel 7.  Which leads me to another question:  Does it cause many problems when you mix and match Etherchannel bundles with just single cable STP connections?
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Expert Comment

by:Don Johnston
ID: 34902819
> Does it cause many problems when you mix and match Etherchannel bundles with just single cable STP connections?

I'm not sure I follow your question. A physical link can only be part of one etherchannel.
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Author Comment

by:B1izzard
ID: 34903176
Basically all I meant was in the diagram, where there is the single physical cable between the 2 switches (whereas all others are etherchannel bundles), does this ever cause any unusual problems?  I'm assuming it doesn't matter, as STP will block wherever necessary to prevent loops.

Final question:  In the following, is it necessary to put the the 'switchport mode trunk' and 'switchport trunk allowed vlan 100' in both places as below?  If not, what is correct?  Many thanks!

interface port-channel 1
   switchport mode trunk
   switchport allowed vlan 100
interface f0/1
   channel-group 1 mode desirable
   switchport mode trunk
   switchport trunk alowed vlan 100
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Expert Comment

by:Don Johnston
ID: 34906548
Wait a minute...

Is the link between Switch 0 and Switch 4 one or two physical links???
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Author Comment

by:B1izzard
ID: 34907792
It's 2 physical links in an Etherchannel.  Between switch 0 and 2 it is just one physical link.
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Expert Comment

by:Don Johnston
ID: 34907828
I'm asking specifically about the connection between the 0 and 2 switch. Nothing else.

If it's a single physical link, then there is no etherchannel.
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Author Comment

by:B1izzard
ID: 34907861
Correct.  That was because there were only 6 channels available in Packet Tracer and I couldn't bundle the 7th one.  So I'm assuming that there is no difference to STP whether you run Etherchannel or not, it will just block wherever necessary?
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Expert Comment

by:Don Johnston
ID: 34907948
Sorry. I had a mis-type.

Switch 0 and Switch 4... One physical link or two?
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Author Comment

by:B1izzard
ID: 34909658
Everything has 2 physical links except between switch 0 and switch 2.
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Expert Comment

by:Don Johnston
ID: 34910113
Okay.

So the answer to:

>So I'm assuming that there is no difference to STP whether you run Etherchannel or not, it
> will just block wherever necessary?

Correct.

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Author Comment

by:B1izzard
ID: 34912509
Thanks.  So back to this.

In the following, is it necessary to put the the 'switchport mode trunk' and 'switchport trunk allowed vlan 100' in both places as below on a given switch?  If not, where is the correct placement of these?  I just want to clean up my config to have the absolute minimum required commands to have it functional.  

interface port-channel 1
   switchport mode trunk
   switchport allowed vlan 100
interface f0/1
   channel-group 1 mode desirable
   switchport mode trunk
   switchport trunk alowed vlan 100
interface f0/2
   channel-group 1 mode desirable
   switchport mode trunk
   switchport trunk alowed vlan 100
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Accepted Solution

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Don Johnston earned 500 total points
ID: 34912651
If the channel is built, config changes to the port channel interface will automatically be applied to the physical interfaces.
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Author Closing Comment

by:B1izzard
ID: 34923756
I see.  Thanks!
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