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PCP field being cleared in VLAN if there is subscirber Private-VLAN configured on the same port

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TitlePCP field being cleared in VLAN if there is subscirber Private-VLAN configured on the same port
Symptoms
From 802.1Q standard: for tagged frames, the priority signaled in the PCP field of the tag header is taken to be the received priority.
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In topology like below:
test-vlan <-> [port 1]x440[port 3] <-> test-vlan
#
# x440 VLAN configuration.
#
configure vlan default delete ports all
create vlan "p-net"
configure vlan p-net tag 1359
create vlan "p-sub"
configure vlan p-sub tag 1377
create vlan "test-vlan"
configure vlan test-vlan tag 1422
configure vlan test-vlan add ports 1,3 tagged

Packets being forwarded within VLAN "test-vlan" with a certain PCP value configured:

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When configure private VLAN on the switch and add port 3 as tagged to subscriber VLAN, PCP field will be cleared:
#
# adding configuration of private VLAN
#
create private-vlan "pvlan"
configure private-vlan pvlan add network p-net
configure private-vlan pvlan add subscriber p-sub
configure vlan p-net add ports 2 private-vlan translated
configure vlan p-sub add ports 3 tagged

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Environment
  • All EXOS versions
  • All EXOS platforms except x670G2, x460G2, X450G2
  • 802.1p
Cause
This is a hardware limitation. When the port is a part of subscriber-VLAN, even though for VLANs that doesn’t require VLAN translation, the VLAN header replacement operation takes place but with the same VID. PCP/CFI fields cannot be preserved during this operation.
 
Resolution
This is a hardware limitation. Following platforms are not affected with such limitation and can preserve PCP/CFI values:
  • X670G2
  • X460G2
  • X450G2
Additional notes

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