A common question in CoS configurations is whether removing a BA (DSCP-based) classifier will impact traffic when an MF (multifield) classifier is already in use. This article explains what happens and what to watch out for.

You have the following BA classifier configured using DSCP values:

set class-of-service classifiers dscp traffic-class forwarding-class f0 loss-priority low code-points 001010

...

set class-of-service classifiers dscp traffic-class forwarding-class f4 loss-priority low code-points 011110

You also have a multifield classifier (MF) configured via firewall filters

You want to know: Is it safe to remove the BA classifier?

MF Classifiers Take Precedence

• In Junos, if both MF and BA classifiers are configured, MF classifier wins
• So if your MF classifier covers all relevant traffic, you can safely remove the BA classifier

Potential Impact of Removal

• BA classifiers act as a fallback: If traffic doesn't match any MF rules, it falls back to BA classification
• If you remove the BA config and some traffic isn’t caught by the MF rules, that traffic will end up unclassified or improperly queued

Recommendation:

Before removing the BA classifier:

1. Double-check your MF classifier – make sure it covers all traffic classes you care about
2. Optionally, test in a lab or maintenance window to verify behavior
3. Monitor queues and forwarding classes after removal to confirm proper classification