The JUNOS software classifies all incoming IPv4 traffic based on the value of the IPv4 ToS precedence bits. To use the JUNOS CoS features to differentiate service types, do one or more of the following:
For a configuration example, see Examples: Classify and Map Input IPv4 Packets.
When classifying incoming IPv4 traffic, you can map the precedence bits to different output transmission queues (item 1 in Figure 17) or map all the incoming traffic on an interface to a specific output transmission queue (item 2 in Figure 17). These two classification schemes are mutually exclusive.
For each IPv4 traffic stream on a link, you can configure up to four output transmission queues. Each FPC can have a maximum of 16 traffic links, so each FPC can have a total of 64 output transmission queues.
For MPLS traffic, the mapping of CoS bits to output transmission queues is static and cannot be configured.
The application that generates the IPv4 packet controls the value in the ToS field.
The precedence bits in the ToS field of the IP packet header comprise the first three bits in the eight-bit ToS field, so there can be eight different precedence values (see Table 15). To configure output transmission queues for CoS, map the eight precedence bit values to the four output queues available on the link. Creating the mapping between the ToS values and the output transmission queues effectively creates the output transmission queues on the FPC.