03-27-2003 11:09 PM - edited 03-02-2019 06:13 AM
[Cat3550]----802.1q trunk----[Cat2950]
The native vlan on the trunk is vlan 2, and vlan 1 is removed from trunk on both devices.
In this case, Catalyst3550 sends CDP frame with untagged, but Catalyst2950 sends CDP frame with vlan1 tagged over the trunk.
(not only the CDP frame, but also the DTP or ethernetLOOPBACK frames are in the same way on both switches)
So, Catalyst2950 can see CDP information of Catalyst3550 but Catalyst3550 can not see that of Catalyst2950.
Two switches can ping each other. Management vlan is vlan2.
Are there anything wrong with the configurations bellow?
If vlan 1 is allowed on the trunk, Catalyst3550 become to understand Catalyst2950's CDP information.
Also, Catalyst3550 begin to send the frames with vlan 1 tagged, for example PVST BPDU for VLAN 1 etc,.
------------------------------------------------
2950#sh run
!
interface FastEthernet0/1
switchport trunk native vlan 2
switchport trunk allowed vlan 2-4094
switchport mode trunk
no ip address
!
!
interface Vlan1
no ip address
no ip route-cache
shutdown
!
interface Vlan2
ip address 172.33.0.100 255.255.255.0
no ip route-cache
!
ip default-gateway 172.33.0.254
ip http server
!
!
end
2950#
2950#sh int trunk
Port Mode Encapsulation Status Native vlan
Fa0/1 on 802.1q trunking 2
Port Vlans allowed on trunk
Fa0/1 2-4094
Port Vlans allowed and active in management domain
Fa0/1 2-3,20,33,49-50,70-73,75,191,200,230,240,250
Port Vlans in spanning tree forwarding state and not pruned
Fa0/1 2-3,20,33,49-50,70-73,75,191,200,230,240,250
2950#
2950#sh cdp ne
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater
Device ID Local Intrfce Holdtme Capability Platform Port ID
C3550_pri Fas 0/1 147 R T S I WS-C3550-1Gig 0/2
2950#
2950#sh int 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: 1 (default)
Trunking Native Mode VLAN: 2 (VLAN0002)
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Operational private-vlan: none
Trunking VLANs Enabled: 2-4094
Pruning VLANs Enabled: 2-1001
Protected: false
Voice VLAN: none (Inactive)
Appliance trust: none
------------------------------------------------
C3550_pri#sh run
!
!
interface GigabitEthernet0/2
switchport trunk encapsulation dot1q
switchport trunk native vlan 2
switchport trunk allowed vlan 2-4094
switchport mode trunk
no ip address
!
interface Vlan1
no ip address
shutdown
!
interface Vlan2
ip address 172.33.0.1 255.255.255.0
ip broadcast-address 172.33.0.255
no ip redirects
no ip mroute-cache
standby 2 ip 172.33.0.254
standby 2 timers 5 15
standby 2 priority 120
standby 2 preempt
standby 2 authentication vlan2
!
interface Vlan3
ip address 172.33.1.1 255.255.255.0
ip broadcast-address 172.33.1.255
no ip redirects
no ip mroute-cache
standby 3 ip 172.33.1.254
standby 3 timers 5 15
standby 3 priority 120
standby 3 preempt
standby 3 authentication vlan3
!
end
C3550_pri#
C3550_pri#sh int trunk
Port Mode Encapsulation Status Native vlan
Gi0/2 on 802.1q trunking 2
Port Vlans allowed on trunk
Gi0/2 2-4094
Port Vlans allowed and active in management domain
Gi0/2 2-3,20,33,49-50,70-73,75,191,200,230,240,250
Port Vlans in spanning tree forwarding state and not pruned
Gi0/2 2-3,20,33,49-50,70-73,75,191,200,230,240,250
C3550_pri#
C3550_pri#sh cdp ne
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater
Device ID Local Intrfce Holdtme Capability Platform Port ID
C3550_pri#sh int switchpo
Name: Gi0/2
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 2 (VLAN0002)
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Operational private-vlan: none
Trunking VLANs Enabled: 2-4094
Pruning VLANs Enabled: 2-1001
Protected: false
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Voice VLAN: none (Inactive)
Appliance trust: none
------------------------------------------------
Thanks.
Solved! Go to Solution.
03-28-2003 12:08 AM
Hi,
generally
"CDP, VTP, and PAgP updates are always forwarded on trunks with a VLAN 1 tag. This is the case even if VLAN 1 has been cleared from the trunks and is not the native VLAN. Clearing VLAN 1 for user data has no impact on control plane traffic that is still sent using VLAN 1."
But there is a bug in Cat3550
"If VLAN 1 or VLANs 1002 to 1005 are removed from a trunk port, the switch no longer receives CDP or VTP frames. VLAN 1 minimization is not supported on the Catalyst 3550 switch. You cannot remove VLAN 1 or VLANs 1002 to 1005 from the allowed VLAN list. (CSCdz22629)"
See Release Notes for the Catalyst 3550 Multilayer Switch Cisco IOS Release 12.1(12c)EA1.
Regards,
Milan
03-28-2003 12:08 AM
Hi,
generally
"CDP, VTP, and PAgP updates are always forwarded on trunks with a VLAN 1 tag. This is the case even if VLAN 1 has been cleared from the trunks and is not the native VLAN. Clearing VLAN 1 for user data has no impact on control plane traffic that is still sent using VLAN 1."
But there is a bug in Cat3550
"If VLAN 1 or VLANs 1002 to 1005 are removed from a trunk port, the switch no longer receives CDP or VTP frames. VLAN 1 minimization is not supported on the Catalyst 3550 switch. You cannot remove VLAN 1 or VLANs 1002 to 1005 from the allowed VLAN list. (CSCdz22629)"
See Release Notes for the Catalyst 3550 Multilayer Switch Cisco IOS Release 12.1(12c)EA1.
Regards,
Milan
03-28-2003 02:12 AM
Milan,
Thanks a lot for your assistance!
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