Supported Platforms
Understanding CoS Classifiers
Packet classification associates incoming packets with a particular class-of-service (CoS) servicing level. Classifiers associate packets with a forwarding class and loss priority, and packets are associated to an output queue based on the forwarding class. You can define classifiers for IPv4 and IPv6 traffic to network interfaces, aggregated Ethernet interfaces (also known as link aggregation groups (LAGs)), integrated routing and bridging (IRB) interfaces (also known as routed VLAN interfaces (RVIs)), Layer 3 interfaces, and Layer 3 VLAN-tagged logical interfaces.
There are two general types of classifiers:
- Behavior aggregate (BA) classifiers
- Multifield (MF) classifiers
You can configure both a BA classifier and an MF classifier on an interface. If you do this, the BA classification is performed first and then the MF classification. If the two classification results conflict, the MF classification result overrides the BA classification result.
On Juniper Networks EX8200 Ethernet Switches, you can specify BA classifiers for bridged multidestination traffic and for IP multidestination traffic. A BA classifier for multicast packets is applied to all interfaces on the EX8200 switch.
 | Note: EX8200 switches implement the on-demand allocation of memory space for ternary content addressable memory (TCAM) so that when additional TCAM space is required for CoS classifiers, it is allocated from the free TCAM space or from the unused TCAM space. An error log message is generated when you configure CoS classifiers to use memory space that exceeds the available TCAM space that includes both the free and unused space. |
This topic describes:
Behavior Aggregate Classifiers
The behavior aggregate classifier maps packets to a forwarding class and a loss priority. The forwarding class determines the output queue for a packet. The loss priority is used by a scheduler to control packet discard during periods of congestion.
There are three types of BA classifiers:
- Differentiated Services Code Point (DSCP) for IP DiffServ
- IP precedence bits
- IEEE 802.1p CoS bits
BA classifiers are based on fixed-length fields, which makes them computationally more efficient than MF classifiers. Therefore core devices, which handle high traffic volumes, are normally configured to perform BA classification.
Default Behavior Aggregate Classification
Juniper Networks Junos operating system (Junos OS) automatically assigns implicit default BA classifiers to logical interfaces based on the type of interface. Table 1 lists different types of interfaces and the corresponding implicit default BA classification.
Table 1: Default BA Classification
Type of Interface | Default BA Classification |
|---|---|
Trunk and Circuit Cross-Connect (CCC) interfaces | ieee8021p-default Note: This BA classification for a CCC interface is applicable only for EX8200 switches. |
Layer 3 interface (IPv4) | dscp-default |
Layer 3 interface (IPv6) | dscp-ipv6-default |
Access interface | Untrusted |
No default classification | |
MPLS | EXP Note: This BA classification is applicable only for EX8200 switches. |
When you explicitly associate a BA classifier with a logical interface, you are overriding the implicit (default) BA classifier with an explicit BA classifier.
Table 2 describes the BA classifier types you can configure on Layer 2 and Layer 3 interfaces.
Table 2: Allowed BA Classification
Type of Interface | Allowed BA Classification |
|---|---|
Layer 2 interface | IEEE 802.1p, IP precedence, DSCP, DSCP IPv6 |
Layer 3 interface (IPv4) | IEEE 802.1p, IP precedence, DSCP |
Layer 3 interface (IPv6) | IEEE 802.1p, IP precedence, DSCP IPv6 |
You can configure all the allowed classifier types on the same logical interface or on different logical interfaces. If you need to apply all classifier rules on the same logical interface, configure the classifier rules allowed for both IPv4 and IPv6 on the logical interface.
If you have not explicitly configured a classifier on a logical interface, the default classifiers are assigned and classification works as follows:
- To a logical interface configured with an IPv4 address, a DSCP classifier is assigned by default, and IPv4 and IPv6 packets are classified using the DSCP classifier.
- To logical interface configured with an IPv6 address, a DSCP IPv6 classifier is assigned by default, and IPv4 and IPv6 packets are classified using the DSCP IPv6 classifier.
| Note: On EX8200 switches, you can configure either one classifier of type DSCP or IEEE802.1p, or you can configure one classifier each of type DSCP and IEEE802.1p. |
You can configure integrated routing and bridging (IRB) interfaces (also known as routed VLAN interfaces (RVIs)) to classify packets. After you do this, the User Priority (UP) bits in the incoming packets are rewritten according to the default IEEE 802.1p rewrite rule, except on EX8200 switches. On EX8200 switches, you must explicitly assign the default IEEE 802.1p rewrite rule to RVIs.
| Note: By default, all BA classifiers classify traffic into either the best-effort forwarding class or the network-control forwarding class. |
Multifield Classifiers
Multifield classifiers examine multiple fields in a packet such as source and destination addresses and source and destination port numbers of the packet. With MF classifiers, you set the forwarding class and loss priority of a packet based on firewall filter rules.
MF classification is normally performed at the network edge because of the general lack of support for DSCP or IP precedence classifiers in end-user applications. On an edge switch, an MF classifier provides the filtering functionality that scans through a variety of packet fields to determine the forwarding class for a packet. Typically, any classifier performs matching operations on the selected fields against a configured value.
