Cambium PMP 450 AP, User Manual

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Chapter 3: System planning Data network planning
Page 3-40
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 VLAN is enabled, immediately monitor traffic to ensure that the results are as desired. For example,
high-priority traffic may block low-priority.
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 81 .
Table 81 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/BHM. The Q-in-Q EtherType parameter is configured with a default EtherType of 0x88a8 in
addition to four alternate EtherTypes 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.