Pre-classification

Pre-classification provides drop protection for ingress packets accessing the 7730 SXR chipset to prevent low priority packets from starving high priority packets before the SR Linux software can perform ingress classification.

The system-wide settings under qos resource-management pre-classification define which packet types the pre-classifier protects from being dropped. During periods of congestion, unlisted packet types may be dropped, in which case the interface drop counters are incremented.

The following table describes the supported pre-classifier types.

Table 1. Pre-classifier types
Pre-classifier type Description
dscp Provides protection for tagged or untagged IPv4 and IPv6 packets (with outer Ethertype of IPv4 or IPv6)
mpls-traffic-class Provides protection for tagged or untagged MPLS packets (with outer Ethertype of MPLS)
dot1p Provides protection for tagged packets that are not IPv4, IPv6, or MPLS

No protection is available for untagged packets that are not IPv4, IPv6, or MPLS.

Protected control packets

In addition to the custom-defined protected packet types, the pre-classifier automatically protects all control packets from the following protocols:

  • ARP
  • PPPoE
  • LLDP
  • MACSEC
  • PBB
  • CFM
  • ICMPv6
  • IGMP
  • RSVP
  • EIGRP
  • VRRP
  • IPSec
  • ISIS
  • LACP
  • ESMC
  • PIM
  • LDP
  • OSPF
  • BGP
  • PIM-Register
  • PIM-RegisterStop
  • ELMI
  • Dot1x
  • EFM-OAM
  • PTP

Default pre-classifier settings

The following are the default pre-classification settings.

--{ candidate shared default }--[  ]--
# info with-context from state qos resource-management pre-classification
    qos {
        resource-management {
            pre-classification {
                dot1p 6 {
                    action protect
                }
                dot1p 7 {
                    action protect
                }
                dscp 48 {
                    action protect
                }
                dscp 56 {
                    action protect
                }
                mpls-traffic-class 6 {
                    action protect
                }
                mpls-traffic-class 7 {
                    action protect
                }
            }
        }
    }

Configuring the pre-classifier

To configure the pre-classifier, use the qos resource-management pre-classification command.

Configure the pre-classifier

The following example configures the pre-classifier to protect packets with a dot1p value of 6, a DSCP value of CS0, or an MPLS traffic-class value of 6. 

--{ candidate shared default }--[  ]--
# info with-context qos resource-management pre-classification
    qos {
        resource-management {
            pre-classification {
                dot1p 6 {
                    action protect
                }
                dscp CS0 {
                    action protect
                }
                mpls-traffic-class 6 {
                    action protect
                }
            }
        }
    }