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Contents
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
IPv6 packets are forwarded by paths that are different from those for IPv4. QoS features supported for IPv6 environments include packet classification, queuing, traffic shaping, weighted random early detection (WRED), class-based packet marking, and policing of IPv6 packets. These features are available at both the process switching and Cisco Express Forwarding switching paths of IPv6.
All of the QoS features available for IPv6 environments are managed from the modular QoS command-line interface (MQC). The MQC allows you to define traffic classes, create and configure traffic policies (policy maps), and then attach those traffic policies to interfaces.
To implement QoS in networks that are running IPv6, follow the same steps that you would follow to implement QoS in networks running only IPv4. At a very high level, the basic steps for implementing QoS are as follows:
You can create a policy to mark each class of traffic with appropriate priority values, using either DSCP or precedence. Class-based marking allows you to set the IPv6 precedence and DSCP values for traffic management. The traffic is marked as it enters the router on the ingress interface. The markings are used to treat the traffic (forward, queue) as it leaves the router on the egress interface. Always mark and treat the traffic as close as possible to its source.
Congestion management for IPv6 is similar to IPv4, and the commands used to configure queueing and traffic shaping features for IPv6 environments are the same commands as those used for IPv4. Traffic shaping allows you to limit the packet dequeue rate by holding additional packets in the queues and forwarding them as specified by parameters configured for traffic shaping features. Traffic shaping uses flow-based queueing by default. CBWFQ can be used to classify and prioritize the packets. Class-based policer and generic traffic shaping (GTS) or Frame Relay traffic shaping (FRTS) can be used for conditioning and policing traffic.
Perform this task to establish the match criteria to be used to match packets for classifying network traffic.
1.
enable
2.
configure
terminal
3.
policy
map
policy-map-name
4.
class
{class-name
|
class-default}
The following example shows how to use the match precedence command to manage IPv6 traffic flows:
Device# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Device(config)# class-m c1 Device(config-cmap)# match precedence 5 Device(config-cmap)# end Device# Device(config)# policy p1 Device(config-pmap)# class c1 Device(config-pmap-c)# police 10000 conform set-prec-trans 4
To verify that packet marking is working as expected, use the show policy command. The output of this command shows a difference between the number of total packets and the number of packets marked.
Device# show policy p1
Policy Map p1
Class c1
police 10000 1500 1500 conform-action set-prec-transmit 4 exceed-action drop
Device# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Device(config)# interface serial 4/1
Device(config-if)# service out p1
Device(config-if)# end
Device# show policy interface s4/1
Serial4/1
Service-policy output: p1
Class-map: c1 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: precedence 5
police:
10000 bps, 1500 limit, 1500 extended limit
conformed 0 packets, 0 bytes; action: set-prec-transmit 4
exceeded 0 packets, 0 bytes; action: drop
conformed 0 bps, exceed 0 bps violate 0 bps
Class-map: class-default (match-any)
10 packets, 1486 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
During periods of transmit congestion at the outgoing interface, packets arrive faster than the interface can send them. It is helpful to know how to interpret the output of the show policy-map interface command, which is useful for monitoring the results of a service policy created with Cisco’s MQC.
Congestion typically occurs when a fast ingress interface feeds a relatively slow egress interface. Functionally, congestion is defined as filling the transmit ring on the interface (a ring is a special buffer control structure). Every interface supports a pair of rings: a receive ring for receiving packets and a transmit ring for sending packets. The size of the rings varies with the interface controller and with the bandwidth of the interface or virtual circuit (VC). As in the following example, use the show atm vc vcd command to display the value of the transmit ring on a PA-A3 ATM port adapter.
Device# show atm vc 3 ATM5/0.2: VCD: 3, VPI: 2, VCI: 2 VBR-NRT, PeakRate: 30000, Average Rate: 20000, Burst Cells: 94 AAL5-LLC/SNAP, etype:0x0, Flags: 0x20, VCmode: 0x0 OAM frequency: 0 second(s) PA TxRingLimit: 10 InARP frequency: 15 minutes(s) Transmit priority 2 InPkts: 0, OutPkts: 0, InBytes: 0, OutBytes: 0 InPRoc: 0, OutPRoc: 0 InFast: 0, OutFast: 0, InAS: 0, OutAS: 0 InPktDrops: 0, OutPktDrops: 0 CrcErrors: 0, SarTimeOuts: 0, OverSizedSDUs: 0 OAM cells received: 0 OAM cells sent: 0 Status: UP
Cisco software (also referred to as the Layer 3 processor) and the interface driver use the transmit ring when moving packets to the physical media. The two processors collaborate in the following way:
The most important aspect of this communication system is that the interface recognizes that its transmit ring is full and throttles the receipt of new packets from the Layer 3 processor system. Thus, when the interface is congested, the drop decision is moved from a random, last-in, first-dropped decision in the first in, first out (FIFO) queue of the transmit ring to a differentiated decision based on IP-level service policies implemented by the Layer 3 processor.
Service policies apply only to packets stored in the Layer 3 queues. The table below illustrates which packets sit in the Layer 3 queue. Locally generated packets are always process-switched and are delivered first to the Layer 3 queue before being passed on to the interface driver. Fast-switched and CEF-switched packets are delivered directly to the transmit ring and sit in the L3 queue only when the transmit ring is full.
|
Packet Type |
Congestion |
Noncongestion |
|---|---|---|
|
Locally generated packets, including Telnet packets and pings |
Yes |
Yes |
|
Other packets that are process-switched |
Yes |
Yes |
|
Packets that are CEF or fast-switched |
Yes |
No |
The following example shows these guidelines applied to the show policy-map interface command output.
Device# show policy-map interface atm 1/0.1
ATM1/0.1: VC 0/100 -
Service-policy output: cbwfq (1283)
Class-map: A (match-all) (1285/2)
28621 packets, 7098008 bytes
5 minute offered rate 10000 bps, drop rate 0 bps
Match: access-group 101 (1289)
Weighted Fair Queueing
Output Queue: Conversation 73
Bandwidth 500 (kbps) Max Threshold 64 (packets)
(pkts matched/bytes matched) 28621/7098008
(depth/total drops/no-buffer drops) 0/0/0
Class-map: B (match-all) (1301/4)
2058 packets, 148176 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: access-group 103 (1305)
Weighted Fair Queueing
Output Queue: Conversation 75
Bandwidth 50 (kbps) Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0
Class-map: class-default (match-any) (1309/0)
19 packets, 968 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any (1313)
The table below defines counters that appear in the example.
|
Counter |
Explanation |
|---|---|
|
28621 packets, 7098008 bytes |
The number of packets matching the criteria of the class. This counter increments whether or not the interface is congested. |
|
(pkts matched/bytes matched) 28621/709800 |
The number of packets matching the criteria of the class when the interface was congested. In other words, the interface’s transmit ring was full, and the driver and the L3 processor system worked together to queue the excess packets in the L3 queues, where the service policy applies. Packets that are process switched always go through the L3 queuing system and therefore increment the "packets matched" counter. |
|
Class-map: B (match-all) (1301/4) |
These numbers define an internal ID used with the CISCO-CLASS-BASED-QOS-MIB. |
|
5 minute offered rate 0 bps, drop rate 0 bps |
Use the load-interval command to change this value and make it a more instantaneous value. The lowest value is 30 seconds; however, statistics displayed in the show policy-map interface command output are updated every 10 seconds. Because the command effectively provides a snapshot at a specific moment, the statistics may not reflect a temporary change in queue size. |
Without congestion, there is no need to queue any excess packets. When congestion occurs, packets, including CEF and fast-switched packets, might go into the Layer 3 queue. If you use congestion management features, packets accumulating at an interface are queued until the interface is free to send them; they are then scheduled according to their assigned priority and the queueing mechanism configured for the interface.
Normally, the packets counter is much larger than the packets matched counter. If the values of the two counters are nearly equal, then the interface is receiving a large number of process-switched packets or is heavily congested. Both of these conditions should be investigated to ensure optimal packet forwarding.
Devices allocate conversation numbers for the queues that are created when the service policy is applied. The following example shows the queues and related information.
Device# show policy-map interface s1/0.1 dlci 100
Serial1/0.1: DLCI 100 -
output : mypolicy
Class voice
Weighted Fair Queueing
Strict Priority
Output Queue: Conversation 72
Bandwidth 16 (kbps) Packets Matched 0
(pkts discards/bytes discards) 0/0
Class immediate-data
Weighted Fair Queueing
Output Queue: Conversation 73
Bandwidth 60 (%) Packets Matched 0
(pkts discards/bytes discards/tail drops) 0/0/0
mean queue depth: 0
drops: class random tail min-th max-th mark-prob
0 0 0 64 128 1/10
1 0 0 71 128 1/10
2 0 0 78 128 1/10
3 0 0 85 128 1/10
4 0 0 92 128 1/10
5 0 0 99 128 1/10
6 0 0 106 128 1/10
7 0 0 113 128 1/10
rsvp 0 0 120 128 1/10
Class priority-data
Weighted Fair Queueing
Output Queue: Conversation 74
Bandwidth 40 (%) Packets Matched 0 Max Threshold 64 (packets)
(pkts discards/bytes discards/tail drops) 0/0/0
Class class-default
Weighted Fair Queueing
Flow Based Fair Queueing
Maximum Number of Hashed Queues 64 Max Threshold 20 (packets)
Information reported for each class includes the following:
The class-default class is the default class to which traffic is directed, if that traffic does not satisfy the match criteria of other classes whose policy is defined in the policy map. The fair-queue command allows you to specify the number of dynamic queues into which IP flows are sorted and classified. Alternately, devices allocate a default number of queues derived from the bandwidth on the interface or VC. Supported values in either case are a power of two, in a range from 16 to 4096.
The table below lists the default values for interfaces and for ATM permanent virtual circuits (PVCs).
|
Bandwidth Range |
Number of Dynamic Queues |
|---|---|
|
Less than or equal to 64 kbps |
16 |
|
More than 64 kbps and less than or equal to 128 kbps |
32 |
|
More than 128 kbps and less than or equal to 256 kbps |
64 |
|
More than 256 kbps and less than or equal to 512 kbps |
128 |
|
More than 512 kbps |
256 |
The table below lists the default number of dynamic queues in relation to ATM PVC bandwidth.
|
Bandwidth Range |
Number of Dynamic Queues |
|---|---|
|
Less than or equal to 128 kbps |
16 |
|
More than 128 kbps and less than or equal to 512 kbps |
32 |
|
More than 512 kbps and less than or equal to 2000 kbps |
64 |
|
More than 2000 kbps and less than or equal to 8000 kbps |
128 |
|
More than 8000 kbps |
256 |
Based on the number of reserved queues for WFQ, Cisco software assigns a conversation or queue number as shown in the table below.
|
Number |
Type of Traffic |
|---|---|
|
1 to 256 |
General flow-based traffic queues. Traffic that does not match to a user-created class will match to class-default and one of the flow-based queues. |
|
257 to 263 |
Reserved for Cisco Discovery Protocol and for packets marked with an internal high-priority flag. |
|
264 |
Reserved queue for the priority class (classes configured with the priority command). Look for the "Strict Priority" value for the class in the show policy-map interface output. The priority queue uses a conversation ID equal to the number of dynamic queues, plus 8. |
|
265 and higher |
Queues for user-created classes. |
Related Topic |
Document Title |
|---|---|
|
IPv6 addressing and connectivity |
IPv6 Configuration Guide |
|
Cisco IOS commands |
|
|
IPv6 commands |
|
|
Cisco IOS IPv6 features |
|
|
Marking Network Traffic |
“Marking Network Traffic” module |
Standard/RFC |
Title |
|---|---|
|
RFCs for IPv6 |
|
MIB |
MIBs Link |
|---|---|
|
|
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: |
Description |
Link |
|---|---|
|
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Feature Name |
Releases |
Feature Information |
|---|---|---|
|
IPv6 QoS: MQC Packet Marking/Remarking |
12.0(28)S 12.2(33)SRA 12.2(18)SXE2 12.2(13)T 12.3 12.3(2)T 12.4 12.4(2)T |
Class-based marking allows you to set the IPv6 precedence and DSCP values for traffic management. |