Native vlan relation with stp,cdp,vtp,dtp

This is something that i've been meaning to test for a longtime and have eventually gotten around to it.It might be of interest to others...

A tester is directly connected to fa0/1 on a 3550.

interface FastEthernet0/1
switchport trunk encapsulation dot1q
switchport mode trunk
no keepalive
speed 100
duplex full

Switch1#sh int fa0/1 switchport
Name: Fa0/1
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 10 (VLAN0010)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: none
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL

Protected: false
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Appliance trust: none

I've captured the different frames arriving on the tester with the default native vlan 1.

PVST+ BPDU

R1(PKTS:4 of 7)#sh 5
=============================================================================
01:15:10.967 UTC Fri Mar 1 2002 Relative Time: 3.631786
Packet 5 of 7 In: FastEthernet0/0

Ethernet Packet: 64 bytes
Dest Addr: 0100.0CCC.CCCD, Source Addr: 0013.8081.C801
IEEE 802.3 length: 50
LLC DSAP: 0xAA, SSAP: 0xAA, Control: 0x03
SNAP OUI: 0x00000C, Protocol: 0x010B

Data:
0 : 0000 0000 0060 0100 1380 81C8 0000 0000 0060 0100 .....`...........`..
20 : 1380 81C8 0080 0100 0014 0002 000F 0000 0000 0002 ....................
40 : 0001 ..

IEEE BPDU

R1(PKTS:4 of

#sh 5
=============================================================================
00:49:22.935 UTC Fri Mar 1 2002 Relative Time: 0.767894
Packet 5 of 8 In: FastEthernet0/0

Ethernet Packet: 60 bytes
Dest Addr: 0180.C200.0000, Source Addr: 0013.8081.C801
IEEE 802.3 length: 38
LLC DSAP: 0x42, SSAP: 0x42, Control: 0x03

IEEE SPANNING TREE Protocol ID: 0x0000, Version: 0x00
Type: 0x00, Flags: 0x00
Root ID: 6001 0013.8081.C800, Root Path Cost: 0x00000000
Bridge ID: 6001 0013.8081.C800, Port ID: 0x8001
Message Age: 0.0, Max Age: 20.0, Hello Time: 2.0, Forward Delay: 15.0

CDP

R1(PKTS:1 of 3)#sh 1
=============================================================================
00:06:51.179 UTC Fri Mar 1 2002 Relative Time: 24.395975
Packet 1 of 3 In: FastEthernet0/0

Ethernet Packet: 387 bytes
Dest Addr: 0100.0CCC.CCCC, Source Addr: 0013.8081.C801
IEEE 802.3 length: 373
LLC DSAP: 0xAA, SSAP: 0xAA, Control: 0x03
SNAP OUI: 0x00000C, Protocol: 0x2000

CDP Cisco Discovery Protocol
Version: 0x02, Time to Live: 0xB4, Checksum: 0xCED5 (OK)
Device ID: Switch1
Version: Cisco IOS Software, C3550 Software (C3550-IPSERVICES-M), Version 12.2(44)SE5, RELEASE SOFTWARE (fc2)
Copyright (c) 1986-2009 by Cisco Systems, Inc.
Compiled Thu 22-Jan-09 02:50 by gereddy
Platform: Cisco WS-C3550-24-PWR
Addresses: 0
Port ID: FastEthernet0/1
Capabilities:
Switch (Level 2 switching).
IGMP conditional filtering.
Protocol-Hello: OUI: 0x00000C, Protocol-ID: 0x0112
Addn'l data: 0000 0000 FFFF FFFF 0102 21FF 0000 0000 0000 0013 8081 C800 FF00 00
VTP Management Domain: cisco
Native VLAN: 10
Duplex Mode: full
Extended Trust: 0 (NO Extended Trust)
COS for Untrusted Ports: 0
Management-Addresses: 1
IP: 0.0.0.0
Power Available: Request-ID: 0, Power-Management-ID: 1
Available-Power: 0, Management-Power-Level: -1

DTP

R1(PKTS:1 of 3)#sh 2
=============================================================================
00:06:57.575 UTC Fri Mar 1 2002 Relative Time: 30.791975
Packet 2 of 3 In: FastEthernet0/0

Ethernet Packet: 60 bytes
Dest Addr: 0100.0CCC.CCCC, Source Addr: 0013.8081.C801
IEEE 802.3 length: 39
LLC DSAP: 0xAA, SSAP: 0xAA, Control: 0x03
SNAP OUI: 0x00000C, Protocol: 0x2004

Data:
0 : 0100 0100 0A63 6973 636F 0000 0200 0581 0003 0005 .....cisco..........
20 : A500 0400 0A00 1380 81C8 0100 0000 0000 0000 ..................

VTP

R1(PKTS:1 of 2)#sh 3
=============================================================================
00:17:19.183 UTC Fri Mar 1 2002 Relative Time: 13.631967
Packet 2 of 2 In: FastEthernet0/0

Ethernet Packet: 99 bytes
Dest Addr: 0100.0CCC.CCCC, Source Addr: 0013.8081.C801
IEEE 802.3 length: 85
LLC DSAP: 0xAA, SSAP: 0xAA, Control: 0x03
SNAP OUI: 0x00000C, Protocol: 0x2003

Data:
0 : 0101 0105 6369 7363 6F00 0000 0000 0000 0000 0000 ....cisco...........
20 : 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 ....................
40 : 0000 0000 3933 3033 3031 3031 3131 3038 DB65 5893 ....930301011108.eX.
60 : 3E6F 2B19 CE7D 84E5 76FA 4C68 0101 0002 00 .o+..}..v.Lh.....

Next, ive modified the native vlan id from its default 1 to 100

Switch1#sh runn int fa0/1
Building configuration...

Current configuration : 193 bytes
!
interface FastEthernet0/1
switchport access vlan 10
switchport trunk encapsulation dot1q
switchport trunk native vlan 100
switchport mode trunk
no keepalive
speed 100
duplex full
end

PVST+ BPDU

R1(PKTS:1 of

#sh 2
=============================================================================
01:10:34.979 UTC Fri Mar 1 2002 Relative Time: 1.144112
Packet 2 of 8 In: FastEthernet0/0

Ethernet Packet: 68 bytes
Dest Addr: 0100.0CCC.CCCD, Source Addr: 0013.8081.C801

DOT1Q Tag ID: 0x8100, Priority: 7, CFI: 0, VLAN ID: 1
Protocol: 0x0032

Data:
0 : AAAA 0300 000C 010B 0000 0000 0060 0100 1380 81C8 .............`......
20 : 0000 0000 0060 0100 1380 81C8 0080 0100 0014 0002 .....`..............
40 : 000F 0000 0000 0002 0001 ..........

IEEE BPDU

R1(CAPTURE:6)#sh 1
=============================================================================
01:10:34.979 UTC Fri Mar 1 2002 Relative Time: 1.144071
Packet 1 of 8 In: FastEthernet0/0

Ethernet Packet: 60 bytes
Dest Addr: 0180.C200.0000, Source Addr: 0013.8081.C801
IEEE 802.3 length: 38
LLC DSAP: 0x42, SSAP: 0x42, Control: 0x03

IEEE SPANNING TREE Protocol ID: 0x0000, Version: 0x00
Type: 0x00, Flags: 0x00
Root ID: 6001 0013.8081.C800, Root Path Cost: 0x00000000
Bridge ID: 6001 0013.8081.C800, Port ID: 0x8001
Message Age: 0.0, Max Age: 20.0, Hello Time: 2.0, Forward Delay: 15.0

VTP

R1(CAPTURE:1)#sh 1
=============================================================================
00:32:36.879 UTC Fri Mar 1 2002 Relative Time: 12.136013
Packet 2 of 2 In: FastEthernet0/0

Ethernet Packet: 354 bytes
Dest Addr: 0100.0CCC.CCCC, Source Addr: 0013.8081.C801

DOT1Q Tag ID: 0x8100, Priority: 0, CFI: 0, VLAN ID: 1
Protocol: 0x0150

Data:
0 : AAAA 0300 000C 2003 0102 0102 4564 0000 0000 0000 ...... .....Ed......
20 : 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 ....................
40 : 0000 0000 0000 0000 1400 0107 0001 05DC 0001 86A1 ....................
60 : 6465 6661 756C 7400 1400 0108 0002 05DC 0001 86A2 default.............
80 : 564C 414E 3030 3032 1400 0108 000A 05DC 0001 86AA VLAN0002............
100 : 564C 414E 3030 3130 1400 0108 0064 05DC 0001 8704 VLAN0010.....d......
120 : 564C 414E 3031 3030 1400 0108 00C8 05DC 0001 8768 VLAN0100...........h
140 : 564C 414E 3032 3030 1800 0109 0190 05DC 0001 8830 VLAN0200...........0
160 : 766F 6970 5F76 6C61 6E00 0000 1400 0108 0258 05DC voip_vlan........X..
180 : 0001 88F8 564C 414E 3036 3030 2000 020C 03EA 05DC ....VLAN0600 .......
200 : 0001 8A8A 6664 6469 2D64 6566 6175 6C74 0101 0000 ....fddi-default....
220 : 0401 0000 2800 0312 03EB 05DC 0001 8A8B 746F 6B65 ....(...........toke
240 : 6E2D 7269 6E67 2D64 6566 6175 6C74 0000 0101 0000 n-ring-default......
260 : 0401 0000 2400 040F 03EC 05DC 0001 8A8C 6664 6469 ....$...........fddi
280 : 6E65 742D 6465 6661 756C 7400 0201 0000 0301 0001 net-default.........
300 : 2400 050D 03ED 05DC 0001 8A8D 7472 6E65 742D 6465 $...........trnet-de
320 : 6661 756C 7400 0000 0201 0000 0301 0002 fault...........

CDP

R1(CAPTURE:2)#sh 2
=============================================================================
00:39:58.391 UTC Fri Mar 1 2002 Relative Time: 27.315961
Packet 2 of 2 In: FastEthernet0/0

Ethernet Packet: 388 bytes
Dest Addr: 0100.0CCC.CCCC, Source Addr: 0013.8081.C801

DOT1Q Tag ID: 0x8100, Priority: 7, CFI: 0, VLAN ID: 1
Protocol: 0x0172

Data:
0 : AAAA 0300 000C 2000 02B4 CBE9 0001 000B 5377 6974 ...... .........Swit
20 : 6368 3100 0500 BF43 6973 636F 2049 4F53 2053 6F66 ch1....Cisco IOS Sof
40 : 7477 6172 652C 2043 3335 3530 2053 6F66 7477 6172 tware, C3550 Softwar
60 : 6520 2843 3335 3530 2D49 5053 4552 5649 4345 532D e (C3550-IPSERVICES-
80 : 4D29 2C20 5665 7273 696F 6E20 3132 2E32 2834 3429 M), Version 12.2(44)
100 : 5345 352C 2052 454C 4541 5345 2053 4F46 5457 4152 SE5, RELEASE SOFTWAR
120 : 4520 2866 6332 290A 436F 7079 7269 6768 7420 2863 E (fc2).Copyright (c
140 : 2920 3139 3836 2D32 3030 3920 6279 2043 6973 636F ) 1986-2009 by Cisco
160 : 2053 7973 7465 6D73 2C20 496E 632E 0A43 6F6D 7069 Systems, Inc..Compi
180 : 6C65 6420 5468 7520 3232 2D4A 616E 2D30 3920 3032 led Thu 22-Jan-09 02
200 : 3A35 3020 6279 2067 6572 6564 6479 0006 0019 4369 :50 by gereddy....Ci
220 : 7363 6F20 5753 2D43 3335 3530 2D32 342D 5057 5200 sco WS-C3550-24-PWR.
240 : 0200 0800 0000 0000 0300 1346 6173 7445 7468 6572 ...........FastEther
260 : 6E65 7430 2F31 0004 0008 0000 0028 0008 0024 0000 net0/1.......(...$..
280 : 0C01 1200 0000 00FF FFFF FF01 0221 FF00 0000 0000 .............!......
300 : 0000 1380 81C8 00FF 0000 0009 0006 4564 000A 0006 ..............Ed....
320 : 0064 000B 0005 0100 1200 0500 0013 0005 0000 1600 .d..................
340 : 1100 0000 0101 01CC 0004 0000 0000 001A 0010 0000 ....................
360 : 0001 0000 0000 FFFF FFFF ..........

DTP

R1(PKTS:2 of 3)#sh 3
=============================================================================
00:27:18.415 UTC Fri Mar 1 2002 Relative Time: 24.271971
Packet 3 of 3 In: FastEthernet0/0

Ethernet Packet: 60 bytes
Dest Addr: 0100.0CCC.CCCC, Source Addr: 0013.8081.C801
IEEE 802.3 length: 36
LLC DSAP: 0xAA, SSAP: 0xAA, Control: 0x03
SNAP OUI: 0x00000C, Protocol: 0x2004

Data:
0 : 0100 0100 0745 6400 0002 0005 8100 0300 05A5 0004 .....Ed.............
20 : 000A 0013 8081 C801 0000 0000 0000 0000 0000 ..................

Conclusion

DTP frames have no association with a vlan and hence are never tagged.
IEEE BPDUs have no association with a vlan and hence are never tagged.

CDP & VTP both belong to vlan 1, if native vlan is 1 they will be untagged, if the native vlan is anything other than 1 they will all be tagged with 1.

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Comments

yuriz43

This is a great post, and it answered some tough questions I had about dot1q tagging and native vlans. I'll be keeping this book marked.

I have one question about your configuration however. In the second series of tests you put your interface into vlan 10. Why did you do this, and how does that work if it is a trunk port at the same time?

kpjungle

One thing to note, is that DTP requires the VTP information (domain name) to be the same.. As far as I remember.

Mrock4

kpjungle wrote: »

One thing to note, is that DTP requires the VTP information (domain name) to be the same.. As far as I remember.

This is right AFAIK. I read on the CCIE Pursuit blog, however, that this does not apply if one switch has no vtp domain configured (null), and the other is configured. Can someone confirm this? I can try it tomorrow, but am currently at work with no access to the equipment.

kpjungle

Mrock4 wrote: »

This is right AFAIK. I read on the CCIE Pursuit blog, however, that this does not apply if one switch has no vtp domain configured (null), and the other is configured. Can someone confirm this? I can try it tomorrow, but am currently at work with no access to the equipment.

I can confirm that. just labbed it up on two switches.. If one switch is in transparent mode with domain name of kplab and the other a fresh server (with domain of null), the trunk will form.

If two different (lala and kplab):
%DTP-5-DOMAINMISMATCH: Unable to perform trunk negotiation on port Gi0/1 because of VTP domain

Mrock4

Thanks KP. That's good to know!

EdTheLad

yuriz43 wrote: »

I have one question about your configuration however. In the second series of tests you put your interface into vlan 10. Why did you do this, and how does that work if it is a trunk port at the same time?

I've just seen your question now, a bit late but anyway.
The first "show int fa0/1" output is missing the "switchport access vlan 10", i must have made a slight error in my recording as it was definitely configured as per the following "sh int fa0/1 switchport" output which indicates access vlan 10.
The port can be configured with an access vlan which means nothing since the port is working in trunk mode.The reason i set the access vlan to 10 was just to have it different than the native vlan for testing sake.

ocsic669

how did you manage to capture the frames? what program/function did you use if you don't mind telling.

thx

jacky_zhang

Have a different test result.

that unless the pvst if the vlan is not native will be tagged, others such as dtp, vtp,cdp , will never get a tag.

Hello author, can you give your comment on this ?

thanks