Question: VLAN 1 By default, VLAN 1 is the native VLAN and should only be used to carry control traffic,
CDP, VTP, PAgP, and DTP. This information is transmitted across trunk links untagged. • User VLANs should not include the native VLAN, VLAN 1. This information will be sent as tagged frames across VLAN trunks. • The Management VLAN should be a VL Now, I am testing vlan 1 so that SW1 can't send vlan 1 to SW2 through trunk by using "switchport trunk allowed vlan remove 1" As I expected the below is the output after i did in SW1 ( SW1 ---- SW2 are connected through f0/15 each other) [image: 1.jpg]<https://learningnetwork.cisco.com/servlet/JiveServlet/showImage/2-212899-92160/1.jpg> Based on what i understood since SW1 can't send vtp, cdp, dtp, udld, pagp, SW2 cann't negotiate dynamically. (No cdp, no vtp information is transfeered) However, when I capture the packet, it is still transferred CDP/VTP/DTP packets each other. [image: 2.jpg]<https://learningnetwork.cisco.com/servlet/JiveServlet/showImage/2-212899-92161/2.jpg> Interestingly, each SW uses multicast address 01 00 0c cc cc cc for this packet. I thought when I block vlan 1, it blocks multicast traffic, too. but, swithes are sending each other all CDP/VTP/DTP information. I rebooted both switches, but they are trunking still. -------------------- f0/15 config --------------- SW1#show run inter f0/15 Building configuration... Current configuration : 149 bytes ! interface FastEthernet0/15 switchport trunk encapsulation dot1q switchport trunk allowed vlan 2-11,13-4094 end SW1# SW2 ! interface FastEthernet0/15 switchport trunk encapsulation dot1q switchport trunk allowed vlan 2-11,13-4094 switchport mode dynamic desirable end SW2# ---------------- show int trunk -------------- SW1#show inter trunk Port Mode Encapsulation Status Native vlan Fa0/15 auto 802.1q trunking 1 Port Vlans allowed on trunk Fa0/15 2-11,13-4094 Port Vlans allowed and active in management domain Fa0/15 200,202,210,300,310 Port Vlans in spanning tree forwarding state and not pruned Fa0/15 200,202,210,300,310 SW1# SW2#show int trunk Port Mode Encapsulation Status Native vlan Fa0/15 desirable 802.1q trunking 1 Port Vlans allowed on trunk Fa0/15 2-11,13-4094 Port Vlans allowed and active in management domain Fa0/15 200,202,210,300,310 Port Vlans in spanning tree forwarding state and not pruned Fa0/15 200,202,210,300,310 SW2# What am i missing here? I like to better understand what vlan 1 does. _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs
