VTP and trunking

singh8281singh8281 Member Posts: 126
in CCNP
Would hardcoded trunk ports ( by hardcoded I mean switchport mode trunk, but negotiation is still on) form a trunk even if two switches are in different vtp domain, I found that even if the trunk is hardcoded, the DTP messages will still be sent on those ports but will be ignored by trunk ports and trunks will form even if the vtp domain name doesn’t match. why would DTP messages be sent at the first place if they are going to be ignored?.
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  • chmorinchmorin Member Posts: 1,446 ■■■■■□□□□□
    singh8281 wrote: »
    Would hardcoded trunk ports ( by hardcoded I mean switchport mode trunk, but negotiation is still on) form a trunk even if two switches are in different vtp domain, I found that even if the trunk is hardcoded, the DTP messages will still be sent on those ports but will be ignored by trunk ports and trunks will form even if the vtp domain name doesn’t match. why would DTP messages be sent at the first place if they are going to be ignored?.

    In case I want to change the VTP domain. I think I did a lab where I had two switches that were not communicating, and they were supposed to. The domain on one did not match the other, so I had to reconfigure it to the correct one.

    I would assume it has something to do with convergence.
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  • singh8281singh8281 Member Posts: 126
    But if both sides are hardcoded trunk, why consume bandwidth by sending DTP packets, when trunk would form, regardless.
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  • networker050184networker050184 Mod Posts: 11,962 Mod
    singh8281 wrote: »
    But if both sides are hardcoded trunk, why consume bandwidth by sending DTP packets, when trunk would form, regardless.


    One side doesn't know if the other is hard coded or not. So, it send the DTP packets to help the other side form the trunk. If you don't want t consume the bandwidth then disable DTP.
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  • tim100tim100 Member Posts: 162
    networker050184 wrote: »
    One side doesn't know if the other is hard coded or not. So, it send the DTP packets to help the other side form the trunk. If you don't want t consume the bandwidth then disable DTP.

    If both sides are specifically configured with "switchport mode trunk" then the interfaces will trunk regardless. The transmitted DTP frames are basically useless in this situation.
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  • tim100tim100 Member Posts: 162
    chmorin wrote: »
    In case I want to change the VTP domain. I think I did a lab where I had two switches that were not communicating, and they were supposed to. The domain on one did not match the other, so I had to reconfigure it to the correct one.

    I would assume it has something to do with convergence.

    You had the interfaces configured as dynamic so you would have a %DTP-5-DOMAINMISMATCH error during negotiation because of the VTP domain mismatch and the trunk would not form. The operational mode would be static access. If the interfaces were hard coded with "switchport mode trunk" the interfaces would have trunked regardless.
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