Negotiate a Trunk

Does anyone know how i can set ports on a 2924 to auto-negotiate a trunk?

I cannot figure out the command even with ios help...

I figured out how to set either ISL or dot1q... but the port still has "Negotiating of Trunking: Disabled"

Find more posts tagged with

Save $250 on 2025 certification boot camps from Infosec!

Book now with code EOY2025

Button

Comments

mikej412

The 2900 XL switches didn't/don't support DTP.

Check out DTP in Table 2. The 2900XL's are the first column.
Catalyst 2950 Series Software Feature Comparison--SI and EI [Cisco Catalyst 2950 Series Switches] - Cisco Systems

bigheadx

What he said ^^!

AlexMR

Also, you can't have both switchports set to dynamic auto because they will always become an access port. One of them must be configured as a trunk...or dynamic desirable.

ColbyG

AlexMR wrote: »

Also, you can't have both switchports trying set to dynamic negociate auto because they will always become an access port. One of them must be coonfigured as a trunk.

wat...?

Bl8ckr0uter

AlexMR wrote: »

Also, you can't have both switchports trying set to dynamic negociate auto because they will always become an access port. One of them must be coonfigured as a trunk.

By default the ports are to Dynamic Auto. So they will become trunks by default since Dynamic auto will become trunks if neighbor ports are set to Auto/Desirable/Trunk. I believe that if the neighbor port is set to access the port will become access. I know that this applies to the 2950 but I am not sure about any others.

I pulled this from my notes, which were based on the CCNA study guide.

rwwest7

AlexMR wrote: »

Also, you can't have both switchports trying set to dynamic negociate auto because they will always become an access port. One of them must be coonfigured as a trunk.

The whole point of the dynamic thing is so people can pull switches out of the box, plug them in, and be trunking without knowing even what trunking is.

luke_bibby

AlexMR wrote: »

Also, you can't have both switchports trying set to dynamic negociate auto because they will always become an access port. One of them must be coonfigured as a trunk.

I think what you meant was that if two connected switches are configured as "dynamic auto" then neither switch will send a DTP frame to negotiate the trunk, and thus no trunk will be formed. If one is configured as "trunk" or "dynamic desirable" then a trunk will form with the other being set to "dynamic auto"

knwminus wrote: »

By default the ports are to Dynamic Auto. So they will become trunks by default since Dynamic auto will become trunks if neighbor ports are set to Auto/Desirable/Trunk. I believe that if the neighbor port is set to access the port will become access. I know that this applies to the 2950 but I am not sure about any others.

Two "dynamic auto" configurations will not form a trunk. 2950's also default to "dynamic desirable" by the way :P

rwwest7

Cisco Certification Exam Review Trunking Modes 2950 Switch

dynamic desirable: Default for many new Cisco switches, a port in this mode is actively attempting to form a trunk via Dynamic Trunking Protocol (DTP).
dynamic auto: A port in this mode will form a trunk, but is not actively attempting to negotiate trunking, so DTP frames are not transmitted.

AlexMR

Ok. It was late, I was tired from studying like 100 hours for the CCNA voice and I mistyped "trying". Now I edited my post and i think it is correct.

rwwest7 wrote: »

The whole point of the dynamic thing is so people can pull switches out of the box, plug them in, and be trunking without knowing even what trunking is.

I'm pretty sure this is incorrect. They negotiate a trunk out of the box because they are dynamic/desirable by default. I might be wrong about it but I doubt I am.

luke_bibby wrote: »

I think what you meant was that if two connected switches are configured as "dynamic auto" then neither switch will send a DTP frame to negotiate the trunk, and thus no trunk will be formed. If one is configured as "trunk" or "dynamic desirable" then a trunk will form with the other being set to "dynamic auto"

Two "dynamic auto" configurations will not form a trunk. 2950's also default to "dynamic desirable" by the way :P

You got it right, Luke.

mikej412

The question was about a 2924 switch. It doesn't support DTP so there are NO negeotion options.

The only trunking options on the 2924 are setting the encapsulation and statically configuring the interface so that it forms a trunk.

Answering a question that wasn't asked is confusing when people search the forum for 2924 and trunking or DTP and find information in the thread that isn't relevant.

If you want to discuss dynamic desirable and dynamic auto -- it's been done recently in this thread
http://www.techexams.net/forums/ccna-ccent/46821-does-tagging-encapsulation-always-occur.html

mikej412 wrote: »

ISL Trunks will always tag traffic

Trunking depends on the switches.

2924-XL-EN switches don't support DTP, so you have manually tell a port to trunk.

2950 switches will attempt to trunk by default -- but only support dot1q. I assume the 2960 is the same.

3550 switches default to dynamic desirable -- so they will trunk with other 3550 switches -- and 3560 switches and 3750 switches which default to dynamic auto.

3560 (and 3750) default to dynamic auto -- and 2 dynamic auto switches will NOT negotiate a trunk. You'd have to change the default configuration on at least one switch to get it to trunk.

rwwest7

AlexMR wrote: »

I'm pretty sure this is incorrect. They negotiate a trunk out of the box because they are dynamic/desirable by default. I might be wrong about it but I doubt I am.

You say I'm wrong, then you say the same thing I did. They negotiate trunk out of the box. Thank you.

ncsugrad2002

rwwest7 wrote: »

You say I'm wrong, then you say the same thing I did. They negotiate trunk out of the box. Thank you.

lol, i was thinking the same thing.. you guys said the exact same thing but were disagreeing? haha.

and yes, that is correct--FOR SWITCHES THAT SUPPORT TRUNKING. the 2924 does not.

AlexMR

LOL. I sent him a PM. I was trying to quote the preceding post.

Morty3

ncsugrad2002 wrote: »

lol, i was thinking the same thing.. you guys said the exact same thing but were disagreeing? haha.

and yes, that is correct--FOR SWITCHES THAT SUPPORT TRUNKING. the 2924 does not.

Haha, for switches that support dynamic trunking. The 2924 does not. It does support trunking, though it is a lil different on these switches. I think it is called like "Multi" or something. Not sure on this, I remember it was different though. Had a few in my schools lab.