I have connected two Cisco Catalyst 3560 switches together by a pair of fibre cables. No trunk was formed.
The default interface configuration for Catalyst 3560 is dynamic auto, in Catalyst 3550 the default was dynamic desirable.
Dynamic desirable is actively negotiating a trunk with another cisco catalyst switch, whereas dynamic auto is passively waiting for another cisco catalyst switch to initiate the trunking negotiation. Base on this it is not hard to analyze this:
dynamic desirable + dynamic desirable = trunk
dynamic desirable + dynamic auto = trunk
dynamic auto + dynamic auto = no trunk
Sw2-3560#sh interface trunk Sw2-3560#sh interface gi0/1 switchport Name: Gi0/1 Switchport: Enabled Administrative Mode: dynamic auto Operational Mode: static access Administrative Trunking Encapsulation: negotiate Operational Trunking Encapsulation: native Negotiation of Trunking: On Access Mode VLAN: 1 (default) 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 Sw2-3560#
Sw2-3560#sh interface trunk Sw2-3560#
As shown above no trunk was established.
Configure one of the switch to be dynamic desirable
Sw2-3560#conf t Enter configuration commands, one per line. End with CNTL/Z. Sw2-3560(config)#interface range gi0/1-2 Sw2-3560(config-if-range)#switchport mode dynamic desirable Sw2-3560(config-if-range)#end Sw2-3560# *Mar 1 00:17:58.036: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed state to down *Mar 1 00:17:58.045: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/2, changed state to down *Mar 1 00:17:58.858: %SYS-5-CONFIG_I: Configured from console by console Sw2-3560# *Mar 1 00:18:01.056: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed state to up *Mar 1 00:18:01.073: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/2, changed state to up Sw2-3560# Sw2-3560#
Sw2-3560#sh int trunk Port Mode Encapsulation Status Native vlan Gi0/1 desirable n-isl trunking 1 Gi0/2 desirable n-isl trunking 1 Port Vlans allowed on trunk Gi0/1 1-4094 Gi0/2 1-4094 Port Vlans allowed and active in management domain Gi0/1 1,100,200,300,400,500,600 Gi0/2 1,100,200,300,400,500,600 Port Vlans in spanning tree forwarding state and not pruned Gi0/1 1,100,200,300,400,500,600 Gi0/2 none Sw2-3560#
Trunk
Trunk is a term used by Cisco, other vendors do not use this term. The idea of trunk is it transports all vlans by default including native vlan 1. User can prune it or set the allowed vlans to traverse across the trunk links.
In Hirschmann switches, the use of trunk is known as tagged link. Vlan that needs to be transported over the switch link has to be tagged with respective Vlan id, Cisco switches did this tagging automatically with switchport mode trunk or by using dynamic desirable and auto combination. Hirschmann switches also have Vlan1 which is the default Vlan, Vlan 1 is untagged by default which behaves the same as Cisco native Vlan 1.
Command example of Hirschmann switch for Vlan
enable vlan database vlan 10 exit configure interface 1/1 vlan participate include 20 vlan tagging 20 exit exit
The above tags vlan20 for egress port 1/1.
enable configure interface 1/2 vlan participate include 20 vlan pvid 20
the above untagged vlan 20 for egress port 1/2, this effectively is the same as Cisco command:
switchport mode access switchport access vlan 20
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