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Beginner

Tagged and untagged traffic (802.1q)

Good Morning All,

I have a quick question. Concept of native vlan and dtp is clear. No need of link to both concept.

Target of the test -> Test the behaviour of Native Vlan. Create untagged traffic and check if it is carried over the native vlan.

Test Preparation

  • Create untagged traffic between R3 and R2
  • How to create untagged traffic -> Set interfaces (R2-f1/1 and R3 f1/0) in access mode (I think here is the problem)
  • R2-f1/0, R1-f1/0 -> Trunk interfaces. Allowed vlan 20,30. Native vlan 20
  • SVI - R1 vlan 20,30 --  R2-vlan 20  -- R3 vlan 20

What is working -> Ping from vlan 20 between R2 and R1

What is not working -> Ping from vlan 20 between R3<->R2, R3<->R1

R3 is sending the arp request but it does not receive any reply. R1, R2, R3 have all vlan 20 defined so they belong to the same broadcast domain.

All the involved interfaces are in forwading (STP)

What am I missing?

Curious about the reply.

1 ACCEPTED SOLUTION

Accepted Solutions
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Hall of Fame Guru

Hi Fabio

Hi Fabio

The second test will work as you found but then so should your original test.

I just did a very quick lab (with an emulator) using 3 switches with your original setup and it worked fine for me.

So not sure what is happening with your setup.

Jon

View solution in original post

4 REPLIES 4
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Hall of Fame Guru

Are these L3 switches ?

Are these L3 switches ?

Assumig they are it should work.

R1 should be able to ping R2 in vlan 10 and 20 and R3 in vlan 20 (assuming you have created SVIs for both vlans).

And the pings should work the other way around as well.

Perhaps something to do with your configuration ?

Jon

Highlighted
Beginner

Hi Jon,

Hi Jon,

Thanks. 

SVI have been created as stated before.

L3 devices yes. Ping is working between R1 and R2.

Configuration should be also ok. 

Wireshark is showing me the arp request leaving the R3 but no reply. It looks like that R3 has a different broadcast domain otherwise I can not explain this behaviour. In any case you confirmed that it should work so at least it makes sense my idea of this lab. I am not sure about the behaviour of the interfaces on R2 and R3 when both are set in access mode.

I did a second test with trunk R2 R3 allowing all vlan and using as Native the 20. It is working. Even in case I leave the native vlan as default, vlan1.

Highlighted
Hall of Fame Guru

Hi Fabio

Hi Fabio

The second test will work as you found but then so should your original test.

I just did a very quick lab (with an emulator) using 3 switches with your original setup and it worked fine for me.

So not sure what is happening with your setup.

Jon

View solution in original post

Highlighted
Beginner

I just need a confirmation

I just need a confirmation that the lab should work.

I investigate offline.

Cheers,

Fabio.

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