FAQs Of Cisco ASR 1000 Aggregation Services Routers Quality of Service (QoS)

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Q. How does the Cisco ASR 1000 calculate packet sizes?

A. Please refer to Table 1 for general information about queuing policy maps applied to physical interfaces, sub-interfaces, ATM virtual circuits, virtual templates or tunnel interfaces. Please refer to Table 2 for general information about policing policy maps applied to physical interfaces, sub-interfaces, ATM virtual circuits, virtual templates or tunnel interfaces.

Table 1. Packet Size Calculation for Queuing Functions and Counters

QoS Target What Is Not Included What Is Included
Ethernet main and sub-interfaces Inter-frame gap (IFG)/preamble and cyclic redundancy check (CRC)

Layer 1 overheads

Layer 2 headers and Layer 2 payload

802.1q header

All Layer 3 and up payloads

ATM virtual circuits and ATM virtual paths Layer 1 overheads 5-byte ATM cell headers

All ATM Adaptation Layer (AAL) headers

AAL CRC values

ATM cell tax and ATM cell padding

All Layer 3 and up payloads

Serial and Packet over SONET (PoS) main interfaces CRC and High-Level Data Link Control (HDLC) bit stuffing Layer 2 headers and Layer 2 payload

All Layer 3 and up payloads

Virtual access, broadband virtual template, and sessions IFG/preamble and CRC

Layer 1 overheads

Layer 2 headers and Layer 2 payload

802.1q header

Layer 2 Tunneling Protocol (L2TP) headers

Point-to-Point Protocol over X (PPPoX) headers

All Layer 3 and up payloads

Tunnels

(generic routing encapsulation [GRE], Dynamic Multipoint VPN [DMVPN], Dynamic Virtual Tunnel Interface [dVTI], IPsec Site-to-Site VPN [sVTI], and IP Security [IPsec])

IFG/preamble and CRC

Layer 1 overheads

Layer 2 headers and Layer 2 payload

802.1q header

GRE headers

Cryptographic headers and trailer

All Layer 3 and up payloads

PPP multilink bundle IFG/pre-amble, CRC

L1 overheads

L2 multilink PPP headers

L2 PPP headers

L2TP headers

ATM cell tax, ATM cell padding

Table 2. Packet Size Calculation for Classification and Policing Functions and Counters in the Egress Direction

QoS Target What Is Not Included What Is Included
Ethernet main and sub-interfaces IFG/preamble, and CRC

Layer 1 overheads

Layer 2 headers, Layer 2 payload, 802.1q header, and all Layer 3 and up payloads
ATM virtual circuits and ATM virtual paths 5-byte cell headers, all AAL headers, AAL CRC values, ATM cell tax, ATM cell padding, and all payloads Layer 3 and up payloads
Serial and PoS main interfaces CRC and HDLC bit stuffing Layer 2 headers, Layer 2 payload, and all Layer 3 and up payloads
Virtual access, broadband virtual template, and sessions IFG/preamble and CRC

Layer 1 overheads

Layer 2 headers* and Layer 2 payload

802.1q header

L2TP headers

PPPoX headers

All Layer 3 and up payloads

Tunnel

(GRE, DMVPN, dVTI, sVTI, and IPsec)

IFG/preamble and CRC

Layer 1 overheads

Layer 2 headers and Layer 2 payload

802.1q header

Cryptographic headers and trailers

GRE headers

All Layer 3 and up payloads

PPP multilink bundle IFG/pre-amble, CRC

L1 overheads

ATM cell tax, ATM cell padding

L2 multilink PPP headers

L2 PPP headers

L2TP headers

* Note that for broadband L2TP Network Server (LNS) scenarios, QoS policers configured on sessions will not observe the Layer 2 overhead. So the 14 bytes for Layer 2 source/destination address and Layer 2 type and any 802.1q headers will not be included. As a result, any policers used for priority traffic would not include any overhead accounting offsets that are used for queuing or scheduling decisions.

 

Q. Can QoS be configured on the management interface, GigabitEthernet0?

A. No, you cannot configure QoS on the management interface. The management interface is handled entirely within the route processor, and traffic to and from the management interface does not move through the Cisco ASR 1000 Series Embedded Services Processor (ESP). Because all QoS functions are performed on the ESP, QoS cannot be applied.

 

Q. Is there a difference in QoS behavior on shared port adapter (SPA)-based Ethernet ports compared to built-in Ethernet ports?

A. For QoS behavior managed by MQC service-policy commands, there is no difference in QoS behavior. All advanced QoS processing is done on the ESP and is not affected by the type of ingress Ethernet port.

All ASR 1000 platforms have low- and high-priority queues on a per-port basis in the ingress and egress path. This is the same regardless of a modular or fixed platform design.

SPA Interface Processor (SIP10 and SIP40) line cards engage in slightly different behavior when scheduling ingress traffic and forwarding to the ESP for processing. This variation only comes into play if the SIP10 is oversubscribed with traffic (for example, two 10-GE SPAs installed in a SIP10 attempt to forward more than 10 Gbps of traffic to the ESP for processing). In undersubscribed scenarios, the behavior will be the same on SIP10 and SIP40. For the vast majority of customers, these subtle differences in behavior would not be observed in normal network behavior. It is not recommended to attempt to manipulate the SIP-based QoS behavior without specific instructions to do so.

Egress behavior is the same between SIP10 and SIP40. The Cisco ASR 1002 Router has a built-in SIP10. The ASR 1002-X Router has a built-in SIP40. In both the ASR 1002 and ASR 1002-X Routers, the built-in SIP is always undersubscribed. The ASR 1001-X Router does not have a built-in SIP as Ethernet interfaces are managed directly by an integrated chipset. The ASR 1001-X has a reduced amount of ingress packet buffer compared to the other ASR 1000 platforms.

 

Q. Can QoS manage control-plane traffic that is destined for Cisco IOS Software running on the route processor?

A. Yes, a nonqueuing QoS policy map is supported on the control plane in Cisco IOS Software configuration mode. This feature is known as CoPP (Control Plane Policing). Usually, a policy map is applied to the control plane to protect the route processor from denial-of-service (DoS) attacks. A policy map applied in the input direction on the control plane will affect traffic that is destined for the route processor from regular interfaces. It is possible to classify packets such that some are rate limited and others are not.

When using show plat hardware qfp commands on the control-plane interface, keep in mind that even though the policy map is configured as “ingress” to the control plane, it is egress from the ESP card. Thus, the show plat hardware qfp commands must use the output direction.

 

Q. How does the three-parameter scheduler used by the Cisco ASR 1000 differ from two-parameter schedulers used by other platforms?

A. The Cisco ASR1000 QoS scheduler uses three parameters: maximum, minimum, and excess. Most other platforms use only two parameters: maximum and minimum.

Both models handle maximum (shape) and minimum (bandwidth) the same way. The difference is how they distribute excess (bandwidth remaining). Maximum is an upper limit of the bandwidth of traffic that a class is allowed to forward. Minimum is a guarantee that the given amount of traffic will always be available, even if the interface or hierarchy is congested.

Excess is the difference between the maximum possible rate (parent shaper) and all the used minimum (priority and bandwidth-guaranteed traffic). A two-parameter scheduler distributes the excess bandwidth proportionally according to the minimum rates. A three-parameter scheduler has a programmable parameter to control that sharing. By default, the Cisco ASR 1000 uses equal sharing or excess values of 1 for every class. Because of restrictions in Cisco IOS Software, you cannot configure the minimum (bandwidth) and excess (bandwith remaining) parameters at the same time in a class. This concurrent configuration was supported in classic Cisco IOS Software.

 

Q. What do the non-MQC bandwidth and bandwidth qos-reference commands do and where are they useful?

A. Typically the interface bandwidth command is used on an interface to influence the bandwidth metric that routing protocols use for their path decisions. In certain situations, however, the value given for the bandwidth command can influence QoS. The bandwidth qos-reference interface command was intended to convey to the QoS infrastructure how much bandwidth is available for the downstream tunnel bandwidth. Table 3 details when bandwidth and bandwidth qos-reference are applicable.

Table 3. Uses for Interface bandwidth and bandwidth qos-reference

Command Target Affect
bandwidth

 

Any generic main interface for physical interface

 

Any top-level QoS MQC references for percent-based configuration will use this value for the interface throughput instead of the actual throughput. For example, if bandwidth 5000 is configured on a Gigabit Ethernet interface and a top-level class-default shaper is configured for shape average percent 50, the interface will be limited to 2.5 Mbps of traffic.
bandwidth

 

Any generic sub-interface for a physical interface

 

This command does not affect QoS. QoS applied on a sub-interface is affected by a bandwidth command configured on the corresponding main interface.
bandwidth

 

 

Multilink Point-to-Point Protocol (MLP) bundle

 

Configuring on the actual bundle interface rate limits traffic even without the application of the QoS MQC configuration. Any percent-based configuration that is part of a policy map applied to the bundle uses the bandwidth value for calculations.
bandwidth qos-reference

 

 

GRE tunnel, sVTI tunnel, dVTI tunnel, and virtual template for broadband

 

Any top-level QoS MQC references for percent-based configuration use this value for the maximum throughput instead of the actual throughput for the used physical interface. For example, if bandwidth 5000 is configured on a sVTI tunnel interface and a top-level class-default shaper is configured for shape average percent 50, the tunnel will be limited to 2.5 Mbps of traffic.
bandwidth qos-reference

 

 

Tunnel interface used for DMVPN

 

This command does not affect the QoS MQC configuration. It is essentially ignored for QoS purposes.

 

Q. The Cisco ASR 1000 isnt showing a class-map filter or access control entries (ACE) matches. How can I access the information?

A. By default, the ASR 1000 does not track per class-map filter or per-ACE matches for QoS. However, you can access these statistics by enabling one of the following CLIs:

platform qos match-statistics per-filter     (supported in Cisco IOS XE 3.3)

platform qos match-statistics per-ace        (supported in Cisco IOS XE 3.10)

Note that these commands will not be affective if added to the configuration while any QoS policies are attached to any interfaces. To become effective, all QoS policies must be removed and then reapplied or the router must be rebooted.

 

Q. How many class maps, policy maps, or match rules are supported?

A. Support as of Cisco IOS XE 3.10 is listed in Table 4.

Table 4. Number of Class Maps, Policy Maps, and Match Rules Supported

Cisco IOS XE Software Versions 2.0S-2.2S 2.3S 3.5S-3.9S 3.10S
Number of unique policy maps 1,024 4,096 4,096 16,000 or 4,096*
Number of unique class maps 4,096 4,096 4,096 4,096
Number of classes per policy map 8 256 1,000 1,000
Number of filters per class map 16 16 32 32

* 16,000 for Cisco ASR 1000 Series Route Processor 2 or 3 (RP2 or RP3) with ESP40, ESP100, or ESP200\All other platform combinations are 4096.

 

Q. What is the scalability of packet memory, ternary content addressable memory (TCAM), and queue for various Cisco ASR 1000 hardware devices?

A. Table 5 details that information:

Table 5. Packet Memory, Queue, and TCAM Scalability

ESP Hardware Packet Memory Maximum Queues TCAM Size
ASR1001 64 MB 16,000 5 Mb
ASR1001-X 512 MB 16,000 10 Mb
ASR1002-F 64 MB 64,000 5 Mb
ASR1002-X 512 MB 116,000 40 Mb
ESP5 64 MB 64,000 10 Mb
ESP10 128 MB 128,000 10 Mb
ESP20 256 MB 128,000 40 Mb
ESP40 256 MB 128,000 40 Mb
ESP100 1 GB (two 512-MB) 232,000* 80 Mb
ESP200 2 GB (four 512-MB) 464,000* 160 Mb

* Note that for ESP100 and ESP200, physical ports are associated with a particular QFP complex on the ESP card. In order to fully use all queues, the queues must be distributed among different slots and SPAs in the chassis.

If you’re interested in Cisco ASR 1000 Series Routers, welcome to contact us (cisco@router-switch.com) or order now: Cisco ASR 1000 Aggregation Services Routers.

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