request: DTP types in hex

Could I ask for some kind soul to volunteer to do a packet capture and tell me the DTP type hex value of Dynamic Trunking Protocol datagrams between two switches using the following trunk encapsulation types:

ISL/ISL
ISL/Negotiated
Negotiated/Negotiated

This would be a HUGE help! I only have one ISL-compatible switch in my lab, so I can't test this myself

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Comments

docrice

This might not be exactly what you asked for, but it might get you in the ballpark. If I recall, these hex values might differ depending on the combination of dynamic auto / desireable / nonegotiate.

http://www.kimiushida.com/bitsandpieces/articles/packet_analysis_dtp/

Futura

Is this stuff on the CCNA?

yapchinhoong2010

Hope this helps too.

TOS - Trunk Operational Status
TAS - Trunk Administrative Status
TNS - Trunk Negotiated Status
TOT - Trunk Operational Trunking Encapsulation
TAT - Trunk Administrative Trunking Encapsulation
TNT - Trunk Negotiated Trunking Encapsulation

================================================================================
C3560 dynamic auto <> C3560 dynamic auto
C3560#sh int fa0/1 switchport | in Administrative Mode|Administrative Trunking|Negotiation
Administrative Mode: dynamic auto
Administrative Trunking Encapsulation: negotiate
Negotiation of Trunking: On
C3560#
C3560#sh dtp int fa0/1 | in TOS|TOT
TOS/TAS/TNS: ACCESS/AUTO/ACCESS
TOT/TAT/TNT: NATIVE/NEGOTIATE/NATIVE
0 bad TLVs, 0 bad TAS, 0 bad TAT, 0 bad TOT, 0 other
C3560#
================================================================================
C3560 dynamic auto <> C2950 dynamic desirable
C3560#sh int fa0/1 switchport | in Administrative Mode|Administrative Trunking|Negotiation
Administrative Mode: dynamic auto
Administrative Trunking Encapsulation: negotiate
Negotiation of Trunking: On
C3560#
C3560#sh dtp int fa0/1 | in TOS|TOT
TOS/TAS/TNS: TRUNK/AUTO/TRUNK
TOT/TAT/TNT: 802.1Q/NEGOTIATE/802.1Q
0 bad TLVs, 0 bad TAS, 0 bad TAT, 0 bad TOT, 0 other
C3560#
================================================================================
C3560 dynamic auto <> Cisco 2600
C3560#sh int fa0/1 switchport | in Administrative Mode|Administrative Trunking|Negotiation
Administrative Mode: dynamic auto
Administrative Trunking Encapsulation: negotiate
Negotiation of Trunking: On
C3560#
C3560#sh dtp int fa0/1 | in TOS|TOT
TOS/TAS/TNS: ACCESS/AUTO/ACCESS
TOT/TAT/TNT: NATIVE/NEGOTIATE/NATIVE
0 bad TLVs, 0 bad TAS, 0 bad TAT, 0 bad TOT, 0 other
C3560#
================================================================================
C3560 dynamic desirable <> C3560 dynamic auto
C3560#sh int fa0/1 switchport | in Administrative Mode|Administrative Trunking|Negotiation
Administrative Mode: dynamic desirable
Administrative Trunking Encapsulation: negotiate
Negotiation of Trunking: On
C3560#
C3560#sh dtp int fa0/1 | in TOS|TOT
TOS/TAS/TNS: TRUNK/DESIRABLE/TRUNK
TOT/TAT/TNT: ISL/NEGOTIATE/ISL
0 bad TLVs, 0 bad TAS, 0 bad TAT, 0 bad TOT, 0 other
C3560#
================================================================================
C3560 switchport trunk encapsulation dot1q, switchport mode trunk <> C3560 dynamic auto
C3560#sh int fa0/1 switchport | in Administrative Mode|Administrative Trunking|Negotiation
Administrative Mode: trunk
Administrative Trunking Encapsulation: dot1q
Negotiation of Trunking: On
C3560#
C3560#sh dtp int fa0/1 | in TOS|TOT
TOS/TAS/TNS: TRUNK/ON/TRUNK
TOT/TAT/TNT: 802.1Q/802.1Q/802.1Q
0 bad TLVs, 0 bad TAS, 0 bad TAT, 0 bad TOT, 0 other
C3560#
================================================================================
C3560 switchport trunk encapsulation dot1q, switchport mode trunk, switchport nonegotiate <> C3560 dynamic auto
C3560#sh int fa0/1 switchport | in Administrative Mode|Administrative Trunking|Negotiation
Administrative Mode: trunk
Administrative Trunking Encapsulation: dot1q
Negotiation of Trunking: Off
C3560#
C3560#sh dtp int fa0/1 | in TOS|TOT
TOS/TAS/TNS: TRUNK/NONEGOTIATE/TRUNK
TOT/TAT/TNT: 802.1Q/802.1Q/802.1Q
0 bad TLVs, 0 bad TAS, 0 bad TAT, 0 bad TOT, 0 other
C3560#
================================================================================
C3560 switchport mode access <> C3560 switchport mode access
C3560#sh int fa0/1 switchport | in Administrative Mode|Administrative Trunking|Negotiation
Administrative Mode: static access
Administrative Trunking Encapsulation: negotiate
Negotiation of Trunking: Off
C3560#
C3560#sh dtp int fa0/1 | in TOS|TOT
TOS/TAS/TNS: ACCESS/OFF/ACCESS
TOT/TAT/TNT: UNKNOWN/NEGOTIATE/UNKNOWN
0 bad TLVs, 0 bad TAS, 0 bad TAT, 0 bad TOT, 0 other
C3560#

yapchinhoong2010

Futura wrote: »

Is this stuff on the CCNA?

nope, DTP is covered on CCNP SWITCH. For CCNA, just need to know about the switchport trunk encapsulation, switchport trunk dynamic desirable, switchport trunk dynamic auto, and switchport mode trunk commands.:)

katachi

Thank you very much for all of your responses. But what I'm looking for is the hex value of the trunk encapsulation type (not the trunking status) as it is found in the datagram itself. For this, a packet capture (on a SPAN port, for example) is necessary.

I've got one switch that only does 802.1Q, and another switch that can do both 802.1Q and ISL, so I already know that a hex value within the type field of the datagram is:

0xa0 = a TOT/TAT of 802.1Q/Negotiate
0xa2 = a TOT/TAT of 802.1Q/ISL
0xa5 = a TOT/TAT of 802.1Q/802.1Q

Unfortunately, I don't have another ISL-capable switch, so I can't find the hex values of other combinations. They can be found by setting SWITCH1 to use ISL (for example), then set SWITCH2 to use ISL as well, and then look at the DTP datagrams in a packet capture to read the hex value of the type field. Depending on how each switch is configured, the DTP datagram it sends will have a different hex value in the type field. These are what I'm curious about.

CodeBlox

Can't you get an old version of Packet Tracer and check the value in simulation mode? In the current version, switches only support IEEE 802.1q. No ISL.

katachi

The oldest version of Packet Tracer I could find was 3.2 (circa 2005?), but it does not seem to support ISL, either.

Also, interestingly, I also tried version 5.1. While you can look at the DTP datagram itself, Cisco inconveniently assumes that you don't want/understand hex values and automatically replaces the actual field hex value with the name of whatever DTP status or type is being sent. Frustrating...

katachi

Got it.

0x42 = a TOT/TAT of ISL/ISL
0x40 = a TOT/TAT of ISL/NEGOTIATE and a TOT/TAT of NEGOTIATE/NEGOTIATE (makes sense, since Cisco documentation says that two switches will default to an ISL trunk encapsulation when both switches support it)