CCIE Routing and Switching Glossary

A Glossary of terms encountered throughout my CCIE journey that I find confusing or difficult to remember:

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CoS - Class of Service - an Ethernet field used when 802.1q tagging is implemented to allow prioritisation of frames.

DF bit - "Do Not Fragment" bit - flag in IP header 'flags' field used to define whether or not the packet should be fragmented. Can be 'set' in a route map for policy routing.

DSCP - Differentiated Services Code Point - a standardised [RFC2474] classification coding for QoS.

DS field - Field in the IP header used to define the packet's traffic classification - aka DiffServ, Differentiated Services - in the past [RFC791 / RFC1349] was called the ToS (Type of Service) field. Now contains DSCP and ECN [RFC2474]. Used in QoS.

IP precedence - Fist three bits in the DS field used to classify IP traffic. Aligns with Ethernet CoS field values. Used in QoS. Can be 'set' in a route map for policy routing.

ToS - Type of Service