Network
Position Incoming
Packet TPID System TPID Match Type Pre-Version
8.2.1.0 Version
8.2.1.0+
0x81XY single-tag first-
byte match
switch to VLAN switch to
default VLAN
Core untagged 0xUVWX — switch to
default VLAN
switch to
default VLAN
double-tag
0xUVWX
0xUVWX double-tag
match
switch to VLAN switch to VLAN
0xUVYZ double-tag
first-byte match
switch to VLAN switch to
default VLAN
0xQRST double-tag
mismatch
switch to
default VLAN
switch to
default VLAN
Egress Access
Point
untagged 0xUVWX — switch to
default VLAN
switch to
default VLAN
double-tag
0xUVWX
0xUVWX double-tag
match
switch to VLAN switch to VLAN
0xUVYZ double-tag
first-byte match
switch to VLAN switch to
default VLAN
0xQRST double-tag
mismatch
switch to
default VLAN
switch to
default VLAN
VLAN Stacking Packet Drop Precedence
The drop eligible indicator (DEI) bit in the S-Tag indicates to a service provider bridge which packets it
should prefer to drop when congested.

Enabling Drop Eligibility

Enable drop eligibility globally before you can honor or mark the DEI value.
When you enable drop eligibility, DEI mapping or marking takes place according to the defaults. In this
case, the CFI is affected according to the following table.
Table 58. Drop Eligibility Behavior
Ingress Egress DEI Disabled DEI Enabled
Normal Port Normal Port Retain CFI Set CFI to 0.
Trunk Port Trunk Port Retain inner tag CFI Retain inner tag CFI.
Retain outer tag CFI Set outer tag CFI to 0.
Access Port Trunk Port Retain inner tag CFI Retain inner tag CFI
Set outer tag CFI to 0 Set outer tag CFI to 0
To enable drop eligibility globally, use the following command.
Service Provider Bridging 833