What is DSCP?

What is DSCP?

The six most significant bits of the DiffServ field is called as the DSCP. The last two Currently Unused (CU) bits in the DiffServ field were not defined within the DiffServ field architecture; these are now used as Explicit Congestion Notification (ECN) bits. Routers at the edge of the network classify packets and mark them with either the IP Precedence or DSCP value in a Diffserv network. Other network devices in the core that support Diffserv use the DSCP value in the IP header to select a PHB behavior for the packet and provide the appropriate QoS treatment.


ToS Byte

P2 P1 P0 T2 T1 T0 CU1 CU0
IP precedence—three bits (P2 to P0)

Delay, Throughput and Reliability—three bits (T2 to T0)

CU (Currently Unused)—two bits(CU1-CU0)


DiffServ Field

DS5 DS4 DS3 DS2 DS1 DS0 ECN ECN
DSCP—six bits (DS5-DS0)



ECN—two bits



References:
https://www.cisco.com/c/en/us/support/docs/quality-of-service-qos/qos-packet-marking/10103-dscpvalues.html