This is a study note post, so please don’t take this as written.  I’m not the authority on the subject, so please correct me if needed.

Back in the day, somebody decided that we all needed to have a Type of Service (ToS) field in the header of IP packets.  Only God knows what this spawn of Satan wanted to do with it, but we’re stuck with it on the CCIE R&S exams.

Here’s another set of notes from my ONT studies.  I’m sure someone will find it useful.  Please help to correct dumbass mistakes.

• Classification is done with traffic desriptors

  • Ingress interface
  • CoS value on ISL or 802.1P frames
  • Source/destination IP address
  • IP Precedence or DSCP value
  • MPLS EXP
  • Application type

• Layer 3 QoS

  • Type of Service (ToS) is 8-bit field.
  • First 3 bits of ToS are the IP precedence.
  • First 6 bits of ToS are the DSCP value.
  • Last 2 bits of ToS are explicit congestion notification (ECN).

• Layer 2 QoS