Reference Guide

902 | Service Provider Bridging
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VLAN Stacking Packet Drop Precedence
VLAN Stacking Packet Drop Precedence is available only on platform: c s
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.
Enable Drop Eligibility
You must enable Drop Eligibility globally before you can honor or mark the DEI value.
When Drop Eligibility is enabled, DEI mapping or marking takes place according to the defaults. In this
case, the CFI is affected according to Table 49-3, "Drop Eligibility Behavior," in Service Provider
Bridging.
Honor the Incoming DEI Value
To honor the incoming DEI value, you must explicitly map the DEI bit to an FTOS drop precedence;
precedence can have one of three colors:
Task Command Syntax Command Mode
Make packets eligible for dropping based on their DEI value. By
default, packets are colored green, and DEI is marked 0 on egress.
dei enable CONFIGURATION
Table 49-3. 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
Precedence Description
Green High priority packets that are the least preferred to be dropped.
Yellow Lower priority packets that are treated as best-effort.
Red Lowest priority packets that are always dropped (regardless of congestion status).