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Switch trunking mode

sudhakara.py
Level 1
Level 1

Hi All

I have a doubt , I hope, one of you will give me quick answer.

Switch 1<--fa0/1-------------------------------fa0/1--> switch 2

switch 1 - Negotiation is disabled, 
interface FastEthernet0/1
switchport mode trunk
switchport nonegotiate

switch 2 - it has negotiation enabled.

interface FastEthernet0/1
switchport mode dynamic auto

My question is , will it form the trunk ? My answer is "NO" (Correct me if I am wrong ), bcz switch 2 side, it is dynamic auto, it creates trunk only if it receives DTP frames from other side, but in other side(Switch 1) , I have disabled the negotiation, so switch 2 won't receive DTP frame, so trunk won't be formed. Am I Correct ? plz answer .

I have tried this topology in packet tracer, in packet tracer, it is forming the trunk,(I think there, packet tracer not working properly ). :) 

3 Replies 3

Furose M
Level 3
Level 3

"switchport mode trunk" will trigger DTP negotiations with peer switch, however, switchport nonegotiate will prevent the switch from sending DTP frames. so, SW2 should not become trunk. however, SW1's side, it will be shown as trunk.

now, due to "order of operation issue, the interface will become trunk on both sides. when you put "switchport mode trunk", both the switches would finish the negotiations before you put the "Switchport nonegotiate". if you do a shut and no shut, you wont see SW2 as trunk/

Hi Furose

Nice explanation.

Thanks for your reply, I tried it on packet tracer, I did shut and no shut, still it is forming trunk. May be something wrong with packet tracer.

I have one more question, if we configure ether channel on router, which protocol will it use( PAGA or LACP) ?

should be a packet tracer issue. in real switches, it works fine.

regarding etherchannel, it depends on which protocol is suppoted in the platform. be in LACP or PAGP.

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