Chapter 3: System planning Data network planningPage 3-34Operators may configure priority precedence as 802.1p Then Diffserv (Default) or Diffserv Then802.1p. Since these priority precedence configurations are independent between the AP and SM,this setting must be configured on both the AP and SM to ensure that the precedence is adhered toby both sides of the link.VLAN settings can also cause the module to convert received non-VLAN packets into VLANpackets. In this case, the 802.1p priority in packets leaving the module is set to the priorityestablished by the DiffServ configuration.If VLAN is enabled, immediately monitor traffic to ensure that the results are as desired. Forexample, 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) taggingwhich 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 trafficacross a network and segregates the broadcast domains of 802.1Q VLANs. Q-in-Q can be usedwith PPPoE and/or NAT.The 802.1ad standard defines the S-VLAN as the Service Provider VLAN and the C-VLAN as thecustomer VLAN. The radio software does 2 layer Q-in-Q whereby the C-VLAN is the 802.1Q tag andthe S-VLAN is the second layer Q tag as shown in Table 69.Table 69 Q-in-Q Ethernet frameEthernet Header S-VLAN EthType0x88a8C-VLAN EthType0x8100 IP Data EthType 0x0800The 802.1ad S-VLAN is the outer VLAN that is configurable on the Configuration > VLAN web pageof the AP/BHM. The Q-in-Q EtherType parameter is configured with a default EtherType of 0x88a8in addition to four alternate EtherTypes that can be configured to aid in interoperability withexisting 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, thisoperates 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 802.1adframe, 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.
