The internal cross-connect used by FPE based PW-port is relying on an MPLS tunnel built over internal network interfaces configured on PXCs. Those internal network interfaces are using a default network policy 1 for egress traffic classification, remarking and marking purposes. Because the PXC cross-connect is MPLS based, the EXP bits in newly added MPLS header is marked according to the default network policy (for brevity reasons, only the relevant parts of the network policy are shown here).
*A:node-1>config>qos>network# info detail
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description "Default network QoS policy."
scope template
egress
fc af
lsp-exp-in-profile 3
lsp-exp-out-profile 2
exit
fc be
lsp-exp-in-profile 0
lsp-exp-out-profile 0
exit
fc ef
lsp-exp-in-profile 5
lsp-exp-out-profile 5
exit
fc h1
lsp-exp-in-profile 6
lsp-exp-out-profile 6
exit
fc h2
lsp-exp-in-profile 4
lsp-exp-out-profile 4
exit
fc l1
lsp-exp-in-profile 3
lsp-exp-out-profile 2
exit
fc l2
lsp-exp-in-profile 1
lsp-exp-out-profile 1
exit
fc nc
lsp-exp-in-profile 7
lsp-exp-out-profile 7
exit
exit
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As seen in this excerpt from the default network egress policy, the forwarding classes AF and L1 marks the EXP bits with the same values. This renders the forwarding classes AF and L1 set on one side of PXC, indistinguishable from each other on the other side of the PXC.
This effectively reduces the number of forwarding classes from 8 to 7 in deployment scenarios where the QoS treatment of traffic depends on preservation of forwarding classes across PXC. That is, in such scenarios, one of the forwarding classes AF or L1 should not be used.