CoS Features and Limitations on M Series and T Series Routers

On IQ2 and IQ2E PICs, the CoS classification and CoS rewrite processes are off-loaded from the FPC to the PIC, so the capabilities and limitations of these types of PICs must be taken into consideration.

For M Series router FPCs, the one-classifier limit includes the default IP precedence classifier. If you create a new classifier and apply it to an interface, the new classifier does not override the default classifier for other interfaces on the same FPC. In general, the first classifier associated with a logical interface is used. The default classifier can be replaced only when a single interface is associated with the default classifier.

Only 58 user-configurable BA classifiers can be attached to logical interfaces on Type-4 FPCs in T640, T1600, or T4000 routers, because six default classifiers are automatically attached to the interfaces. When interfaces on the FPC come up, three default classifiers are installed in the FPC ASIC table: IPv4 and IPv6, MPLS tagging, and multiservices. Next, three default BA classifiers are installed: DSCP IPv6 (9), and MPLS EXP (10), and IP precedence (13).

For user-defined BA classifier types (dscp, dscp-ipv6, ieee-802.1p, ieee-802.1ad, inet-precedence, and mpls-exp), you can attach a maximum of 32 classifiers of the same type (including one default classifier) to a logical interface hosted on a Type-4 FPC in a T640, T1600, or T4000 router.

You can attach a maximum of 8 user-configured BA classifiers of the same type to a logical interface hosted on an Enhanced Scaling FPC in a T640, T1600, or T4000 router.

On all routers, you cannot configure IP precedence and DiffServ code point (DSCP) classifiers on a single logical interface, because both apply to IPv4 packets.

For T Series routers, you can apply separate classifiers for IPv4 and IPv6 packets per logical interface.

For M Series router enhanced FPCs, you cannot apply separate classifiers for IPv4 and IPv6 packets. Classifier assignment works as follows:

• If you assign a DSCP classifier only, IPv4 and IPv6 packets are classified using the DSCP classifier.

• If you assign an IP precedence classifier only, IPv4 and IPv6 packets are classified using the IP precedence classifier. The lower three bits of the DSCP field are ignored because IP precedence mapping requires the upper three bits only.

• If you assign either the DSCP or the IP precedence classifier in conjunction with the DSCP IPv6 classifier, the commit fails.

• If you assign a DSCP IPv6 classifier only, IPv4 and IPv6 packets are classified using the DSCP IPv6 classifier, but the commit displays a warning message.

On M Series router enhanced FPCs and T Series routers, if you associate an IEEE 802.1p classifier with a logical interface, you cannot associate any other classifier with that logical interface.

For most PICs, if you apply an IEEE 802.1p classifier to a logical interface, you cannot apply non-IEEE classifiers on other logical interfaces on the same physical interface. This restriction does not apply to Gigabit Ethernet IQ2 PICs.

On all routers, you cannot assign IP precedence and DSCP classifiers to a single logical interface, because both apply to IPv4 packets.

For M Series router FPCs, only the default MPLS EXP classifier is supported; the default MPLS EXP classifier takes the EXP bits 1 and 2 as the output queue number.

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Allows you to configure up to four loss priorities. Two-rate TCM is supported on T Series routers with Enhanced III FPCs and the T640 Core Router with Enhanced Scaling FPC4.

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Gigabit Ethernet IQ2 PICs support only one queue in the scheduler map with medium-high, high, or strict-high priority. If more than one queue is configured with high or strict-high priority, the one that appears first in the configuration is implemented as strict-high priority. This queue receives unlimited transmission bandwidth. The remaining queues are implemented as low priority, which means they might be starved.

On the IQE PIC, you can rate-limit the strict-high and high queues. Without this limiting, traffic that requires low latency (delay) such as voice can block the transmission of medium-priority and low-priority packets. Unless limited, high and strict-high traffic is always sent before lower priority traffic.

Support for the medium-low and medium-high queuing priority mappings varies by FPC type.

Per-queue output statistics are shown in the output of the show interfaces queue command.

On IQ2 and IQ2E PICs, the CoS classification and CoS rewrite processes are off-loaded from the FPC to the PIC, so the capabilities and limitations of these types of PICs must be taken into consideration.

For M Series router Enhanced FPCs, bits 0 through 5 are rewritten, and bits 6 through 7 are preserved.

For M320 and T Series router non-IQ FPCs, bits 0 through 5 are rewritten, and bits 6 through 7 are preserved.

For M320 and T Series router FPCs, you must decode the loss priority using the firewall filter before you can use loss priority to select the rewrite CoS value.

For M320 and T Series router FPCs, Multiservices and Services PIC link services IQ interfaces (lsq-) do not support DSCP rewrite markers.

For M Series router Enhanced FPCs and M320 and T Series router FPCs, bits 0 through 5 are rewritten, and bits 6 through 7 are preserved.

For M320 and T Series routers FPCs, you must decode the loss priority using the firewall filter before you can use loss priority to select the rewrite CoS value.

For M320 and T Series router FPCs, Multiservices and Services PIC link services IQ interfaces (lsq-) do not support DSCP rewrite markers.

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For M Series router enhanced FPCs and T Series router FPCs, fixed rewrite loss priority determines the value for bit 0; queue number (forwarding class) determines bits 1 and 2. For IQ PICs, you can only configure one IEEE 802.1 rewrite rule on a physical port. All logical ports (units) on that physical port should apply the same IEEE 802.1 rewrite rule.

On T Series routers only, when you configure IEEE 802.1p rewrite marking on Gigabit Ethernet IQ, Gigabit Ethernet IQ2, Gigabit Ethernet Enhanced IQ (IQE), and Gigabit Ethernet Enhanced IQ2 (IQ2E) PICs, you cannot configure more than eight forwarding classes. This limitation does not apply to M Series routers. On M Series routers, you can configure up to 16 forwarding classes when you configure IEEE 802.1p rewrite marking on any of these PICs.

For M Series router FPCs, bits 0 through 2 are rewritten, and bits 3 through 7 are preserved.

For M Series router Enhanced FPCs, bits 0 through 2 are rewritten, bits 3 through 5 are cleared, and bits 6 through 7 are preserved.

For M320 and T Series routers FPCs, bits 0 through 2 are rewritten and bits 3 through 7 are preserved.

For M320 and T Series router FPCs, you must decode the loss priority using the firewall filter before you can use loss priority to select the rewrite CoS value.

For M320 and T Series router FPCs, you must decode the loss priority using the firewall filter before you can use loss priority to select the rewrite CoS value.

For M Series routers FPCs, fixed rewrite loss priority determines the value for bit 0; queue number (forwarding class) determines bits 1 and 2.