02-06-2008 12:50 PM
hi all I have the following setup:
tunnel Port:
interface GigabitEthernet1/0/2
switchport access vlan 784
switchport mode dot1q-tunnel
switchport nonegotiate
l2protocol-tunnel cdp
l2protocol-tunnel stp
l2protocol-tunnel vtp
no cdp enable
spanning-tree portfast
!
Trunk Port - Into Carrier Network
interface GigabitEthernet1/0/25
switchport trunk encapsulation dot1q
switchport trunk native vlan 4094
switchport mode trunk
switchport nonegotiate
load-interval 30
speed nonegotiate
spanning-tree bpdufilter enable
!
the Native Port on the tunnel interface = 1 and native vlan tagging is enabled on the switch.
what happens to untagged frames that hit the tunnel port from the customer? Imagine that they dont have their port as a trunk and are instead emitting untagged frames?
are these dropped or simply have a single Q-tag pushed and are then tunnelled through the carrier network?
I have followed the recommendation of making the trunk port have a native vlan that is not the native vlan of any of the tunnel ports.
thanks
02-12-2008 02:24 PM
You can not get the switch port UP if the other end of the link is not compatible with the config for this port. So, if one side is trunk and the other is not then the port will not come UP. On a trunk line only the frames of native VLAN are sent without any tagging and all other VLAN frames are tagged according to their VLAN numbers.
05-29-2008 06:04 AM
Normally double-tag traffic is seen as NON-IP traffic by metro devices, since they cannot see beyond first tag.
Untagged customer traffic will behave like IP traffic in metro network, since it will have only one tag.
You can use a trick - create an IP access list on trunk port with "deny ip any any" - basically denying all IP traffic. That should stop all traffic that was not tagged by the customer. Ofcourse that will disable your management - so you need to plan this.
If more than one customer is using same S-VLAN, and one customer has e.g. VLAN 3 untagged, and other one has VLAN 5 untagged, their VLANs will be interconnected.
05-29-2008 06:05 AM
Trunk port should have non-default native VLAN on customer side.
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