Watchguard Firebox X20E User Manual page 149

pose.The Edge and other marking-capable external devices use these bits to control how a packet is
handled as it is sent over a network.
The use of marking procedures on a network requires that you do extensive planning. You can first
identify theoretical bandwidth available and then determine which network applications are high pri-
ority, particularly sensitive to latency and jitter, or both.
The Firebox X Edge supports two types of Traffic Control marking: IP Precedence marking and DSCP
(Differentiated Service Code Point) marking. IP Precedence marking affects only the first three bits in
the IP type of service (ToS) octet. DSCP marking expands marking to the first six bits in the IP ToS octet.
With both methods, you can choose to:
Preserve the bits in the header, which may have been marked previously by an external device
•
or
Change the bits to a new value
•
DSCP values can be expressed in numeric form or by special keyword names that correspond to per-
hop behavior (PHB). Per-hop behavior is the priority applied to a packet when traveling from one point
to another in a network. DSCP marking supports three defined types of per-hop behavior:
Best-Effort
Best-Effort is the default type of service and is recommended for traffic that is not critical or real-
time. All traffic falls into this class if you do not use Traffic Control marking.
Assured Forwarding (AF)
Assured Forwarding PHB is recommended for traffic that needs better reliability than the best-
effort service.
Expedited Forwarding (EF)
This type has the highest priority. It is generally reserved for mission-critical and real-time traffic.
Class-Selector (CSx) code points are defined to be backward compatible with Type of Service values.
CS1 through CS7 are identical to the last seven options in the Marking drop-down list when IP Prece-
dence is selected as the marking type.
The following table shows the DSCP values you can select, the corresponding IP Precedence value
(which is the same as the CS value), and the description in PHB keywords.
User Guide
Traffic Marking
137