Problem: Trunk links using DTP aren’t transitioning into a trunk state.
SW02 –
SW02#sh int trunk
SW02#
SW02#sh vtp status
VTP Version : running VTP2
Configuration Revision : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs : 20
VTP Operating Mode : Client
VTP Domain Name : TEST2
VTP Pruning Mode : Disabled
VTP V2 Mode : Enabled
VTP Traps Generation : Disabled
MD5 digest : 0xEA 0xAD 0xAA 0x55 0xAF 0xF7 0x75 0xE7
Configuration last modified by 0.0.0.0 at 3-1-93 01:27:27
SW02#sh run int fa0/3
Building configuration...
Current configuration : 106 bytes
!
interface FastEthernet0/3
switchport trunk encapsulation dot1q
switchport mode dynamic desirable
end
SW01 –
SW01#sh vtp status
VTP Version : running VTP2
Configuration Revision : 23
Maximum VLANs supported locally : 1005
Number of existing VLANs : 20
VTP Operating Mode : Client
VTP Domain Name : TEST
VTP Pruning Mode : Disabled
VTP V2 Mode : Enabled
VTP Traps Generation : Disabled
MD5 digest : 0xAE 0xD8 0xC3 0x52 0x44 0xD4 0x77 0xCE
Configuration last modified by 0.0.0.0 at 3-1-93 01:27:27
SW01#sh run int fa0/3
Building configuration...
Current configuration : 106 bytes
!
interface FastEthernet0/3
switchport trunk encapsulation dot1q
switchport mode dynamic desirable
end
In the above commands, the only item that is mismatching is the VTP domain. Is this why the trunk links aren’t forming?
Verificaton:
SW01 –
SW01#sh dtp
Global DTP information
Sending DTP Hello packets every 30 seconds
Dynamic Trunk timeout is 300 seconds
6 interfaces using DTP
SW01#sh dtp int fa0/3
DTP information for FastEthernet0/3:
TOS/TAS/TNS: ACCESS/DESIRABLE/ACCESS
TOT/TAT/TNT: 802.1Q/802.1Q/802.1Q
Neighbor address 1: 001794BCE683
Neighbor address 2: 000000000000
Hello timer expiration (sec/state): 3/RUNNING
Access timer expiration (sec/state): never/STOPPED
Negotiation timer expiration (sec/state): never/STOPPED
Multidrop timer expiration (sec/state): never/STOPPED
FSM state: S2:ACCESS
# times multi & trunk 0
Enabled: yes
In STP: no
Statistics
----------
128 packets received (99 good)
29 packets dropped
0 nonegotiate, 0 bad version, 29 domain mismatches,
0 bad TLVs, 0 bad TAS, 0 bad TAT, 0 bad TOT, 0 other
131 packets output (131 good)
128 native, 3 software encap isl, 0 isl hardware native
0 output errors
1 trunk timeouts, last timeout on Mon Mar 01 1993, 00:54:43
4 link ups, last link up on Mon Mar 01 1993, 00:01:10
3 link downs, last link down on Mon Mar 01 1993, 00:01:08
Conclusion:
If one were to perform a packet capture, one would see that DTP actually transmits the VTP domain between the switches. If the switches cannot agree on the VTP domain, the switch transitions to an access port. If the trunks are already negotiated, the switch takes 300 seconds to timeout to an access port. Which means the trunks will continue to forward traffic properly for the next 5 minutes.