User guide

Canopy System User Guide Q-in-Q DVLAN (Double-VLAN) Tagging
(802.1AD)
pmp-0229 (Mar 2013)
171
Either way, once the packet leaves the AP, it will be a Q-in-Q frame. For Point-to-Point, it is a little
bit different in that the Backhaul will never add 2 layers of tags to an untagged frame. It will only
add one layer of tag, thus making the frame either a single 802.1Q tagged packet (for untagged
packets), or an 802.1ad doubly-tagged frame for already tagged packets. You can think of it in this
way: the backhaul will only ever add or remove one tag layer, the outermost tag. The multipoint
SM can add or
remove 2, 1, or 0 tags, depending on the packet type and the configuration. In the
upper right of
Figure 54 there is an example packet format showing both tags in place in a Q-in-Q
frame.
SM1, on the top left of Figure 54
, has its VLAN port configured as a Q-in-Q port and also has a
single MAC address VID mapping. For this configuration, the Provider VID, which will be the
outer S-Tag VID, is 80, the Default Port VID, which will be the inner C-Tag VID for devices not
found in the MAC address mapping table, is 10, and finally, the single entry in the MAC-VID
mapping table is VID 11 corresponding to MAC address 00:01:02:03:04:05. Underneath the SM,
there are two PC devices. PC2 has a MAC address that is contained in the MAC address VID table
mapping. So, for
PC2, its effective Port VID will be 11, from the table. For PC1, since it is not in
the table, it will use the Default Port VID which is 10. Once the untagged packets go through the
SM and out of the AP, they will now be Q-in-Q frames with S-Tag VID of 80 and inner C-Tag
VIDs of 10 for PC1 traffic, and 11 for PC2 traffic. These flows will then go across the Backhaul
pair with no modifications to and from the ISP network.
SM2, second from top left in Figure 54 is receiving and sending untagged packets to the client PC
underneath of it. SM has a Default Port VID (Untagged Ingress VID) of 20 and is configured as a
Q VLAN Port type. So, when a packet comes in from the PC and goes out the AP, it will be an
802.1Q tagged packet with VID of 20. On the return path, the SM will strip the Q tag and send the
untagged packet to the PC.
SM3, second from bottom left in Figure 54
, has a client PC underneath of it with an 802.1Q switch
in between that is tagging and untagging traffic from the PC. This switch is putting PC traffic onto
802.1Q VID 25. The SM is configured with a Q-in-Q VLAN Port Type with a Default Port VID of
30. So, when the packet leaves the SM and comes out of the AP, it will be an 802.1ad Q-in-Q
packet with S-Tag VID of 30 and C-Tag VID of 25. On the return path, the 802.1ad Q-in-Q packet
will have its S-Tag stripped and the resulting 802.1Q packet with VID of 25 will be s
ent down to
the switch where it will be further stripped to an untagged packet.