User guide

Canopy System User Guide Q-in-Q DVLAN (Double-VLAN) Tagging
(802.1AD)
pmp-0229 (Mar 2013)
169
Priority on VLANs (802.1p)
The radios can prioritize traffic based on the eight priorities described in the IEEE 802.1p
specification. When the high-priority channel is enabled on an SM, regardless of whether VLAN is
enabled on the AP for the sector, packets received with a priority of 4 through 7 in the 802.1p field
are forwarded onto the high-priority channel.
VLAN settings can also cause the module to convert received non-VLAN packets into VLAN
packets. In this case, the 802.1p priority in packets leaving the module is set to the priority
established by the DiffServ configuration.
If you enable VLAN, immediately monitor traffic to ensure that the results are as desired. For
example, high-priority traffic may block low-priority.
For more information on the high priority channel, see High-priority Bandwidth on Page 86.
Q-in-Q DVLAN (Double-VLAN) Tagging (802.1AD)
PMP and PTP modules can be configured with 802.1ad Q-in-Q DVLAN (Double-VLAN) tagging
which is a way for an operator to put an 802.1Q VLAN inside of an 802.1ad VLAN. A nested
VLAN, which is the original 802.1Q tag and a new second 802.1ad tag, allows for bridging of VLAN
traffic across a network and segregates the broadcast domains of 802.1Q VLANs. Q-in-Q can be
used with PPPoE and/or NAT.
The 802.1ad standard defines the S-VLAN as the Service Provider VLAN and the C-VLAN as the
customer VLAN. The radio software does 2 layer Q-in-Q whereby the C-VLAN is the 802.1Q tag
and the S-VLAN is the second layer Q tag as shown in Table 42.
Table 42: Q-in-Q Ethernet frame
Ethernet Header
S-VLAN EthType
0x88a8
C-VLAN EthType
0x8100
IP Data EthType 0x0800
The 802.1ad S-VLAN is the outer VLAN that is configurable on the Configuration => VLAN web
page of the AP and BHM. The Q-in-Q EtherType parameter is configured with a default EtherType
of 0x88a8 in addition to four alternate EtherType’s that can be configured to aid in interoperability
with existing networks that use a different EtherType than the default.
The C-VLAN is the inner VLAN tag, which is the same as 802.1Q. As a top level concept, this
operates on the outermost tag at any given time, either “pushing” a tag on or “popping” a tag off.
This means packets will at most transition from an 802.1Q frame to an 801.ad frame (with a tag
“pushed” on) or an untagged 802.1 frame (with the tag “popped” off. Similarly, for an 802.1ad frame,
this can only transition from an 802.1ad frame to an 802.1Q frame (with the tag “popped” off) since
the radio software only supports 2 levels of tags.