Configuring VTP

fieldmonkey

In the Odom ICND2 book page 38, it list the steps to configure VTP. As directed in step 6, it states "Bring up trunks between the switches"

Sorry if this is a dumb question, but... what is the action on this step--just plug in the cable or after step 5 is the trunk active?

I think I just answered my question :

Bl8ckr0uter

fieldmonkey wrote: »

In the Odom ICND2 book page 38, it list the steps to configure VTP. As directed in step 6, it states "Bring up trunks between the switches"

Sorry if this is a dumb question, but... what is the action on this step--just plug in the cable or after step 5 is the trunk active?

I think I just answered my question :

Plug in the cable and make sure that the ports are trunks (or have become trunks).
I would say yea.

hexem

You would have to turn on trunking on at least one of the switches, by default catalyst switches are in "dynamic auto" DTP mode, this mean's that they will negotiate trunking with other trunks in the on(trunk), and desirable mode, links between switches in auto mode do not became trunks by default.

Mrock4

hexem wrote: »

You would have to turn on trunking on at least one of the switches, by default catalyst switches are in "dynamic auto" DTP mode, this mean's that they will negotiate trunking with other trunks in the on(trunk), and desirable mode, links between switches in auto mode do not became trunks by default.

2950's and 3550's default to dynamic desirable actually...

3560's default to dynamic auto, and won't trunk in their default mode..that is with another 3560.

---

3550

---

Rack1SW1(config)#default int f0/6
Interface FastEthernet0/6 set to default configuration
Rack1SW1(config)#do sh run int f0/6
Building configuration...

Current configuration : 68 bytes
!
interface FastEthernet0/13
switchport mode dynamic desirable
end

....then I defaulted int f0/13 on SW1 and f0/13 on SW2...no shut..and...

Rack1SW1#sh int trunk

Port Mode Encapsulation Status Native vlan
Fa0/13 desirable n-isl trunking 1


...voila, they're trunking, and default to ISL since they both support ISL and 802.1Q

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Reference: http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a008015bfd6.shtml

Just my $.02

Mrock4

Additionally, ports in dynamic auto DO send DTP packets, but only in response to a received DTP packet. Meaning, a dynamic desirable port would send a DTP packet, dynamic auto one receives it and responds...a trunk is formed..

Dynamic auto port (f0/13)... debug dtp packet below..
Rack1SW1#
02:49:55: DTP-pkt:Fa0/13:Invalid TLV (type 0, len 0) in received packet. ../dyntrk/dyntrk_core.c:1334
02:49:55: DTP-pkt:Fa0/13:Good DTP packet received: ../dyntrk/dyntrk_core.c:1500
02:49:55: DTP-pkt:Fa0/13: Domain: CCIE ../dyntrk/dyntrk_core.c:1503
02:49:55: DTP-pkt:Fa0/13: Status: TOS/TAS = TRUNK/DESIRABLE ../dyntrk/dyntrk_core.c:1506
02:49:55: DTP-pkt:Fa0/13: Type: TOT/TAT = ISL/NEGOTIATED ../dyntrk/dyntrk_core.c:1508
02:49:55: DTP-pkt:Fa0/13: ID: 0013C496BA0D ../dyntrk/dyntrk_core.c:1511
02
Rack1SW1#:49:55: DTP-pkt:Fa0/13:Sending packet ../dyntrk/dyntrk_process.c:1241
02:49:55: DTP-pkt:Fa0/13: TOS/TAS = TRUNK/AUTO ../dyntrk/dyntrk_process.c:1244
02:49:55: DTP-pkt:Fa0/13: TOT/TAT = ISL/NEGOTIATE ../dyntrk/dyntrk_process.c:1247
02:49:55: DTP-pkt:Fa0/13:datagram_out ../dyntrk/dyntrk_process.c:1279

And finally, if the port is configured as such..

switchport trunk encap isl
switchport mode trunk < --- DTP mode ON...

It will STILL send DTP packets out..only if you add

switchport nonegotiate

To the above config will it stop sending DTP..