This chapter is from the book
This chapter is from the book
This chapter is from the book
Foundation Summary
The "Foundation Summary" is a collection of tables and figures that provide a convenient review of many key concepts in this chapter. For those of you already comfortable with the topics in this chapter, this summary can help you recall a few details. For those of you who just read this chapter, this review should help solidify some key facts. For any of you doing your final preparation before the exam, these tables and figures are a convenient way to review the day before the exam.
Figure 3-7 shows the general flow of MQC commands.
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Figure
3-7 MQC Commands and Their Correlation
Table 3-10 lists the match command options available for the IOS revision covered by the current QOS exam, 12.2(15)T.
Table 3-10 match Configuration Command Reference for MQC Tools
|
Command |
Function |
|
match [ip] precedence precedence-value [precedence-value precedence-value precedence-value] |
Matches precedence in IPv4 packets when the ip parameter is included; matches IPv4 and IPv6 packets when the ip parameter is missing. |
|
match access-group {access-group | name access- group-name} |
Matches an ACL by number or name. |
|
match any |
Matches all packets. |
|
match class-map class-map-name |
Matches based on another class map. |
|
match cos cos-value [cos-value cos-value cos-value] |
Matches a CoS value. |
|
match destination-address mac address |
Matches a destination MAC address. |
|
Command |
Function |
|
match fr-dlci dlci-number |
Matches a particular Frame Relay DLCI. |
|
match input-interface interface-name |
Matches an input interface. |
|
match ip dscp ip-dscp-value [ip-dscp-value ip-dscp- value ip-dscp-value ip-dscp-value ip-dscp-value ip- dscp-value ip-dscp-value] |
Matches DSCP in IPv4 packets when the ip parameter is included; matches IPv4 and IPv6 packets when the ip parameter is missing. |
|
match ip rtp starting-port-number port-range |
Matches the RTP's UDP port-number range, even values only. |
|
match mpls experimental number |
Matches an MPLS Experimental value. |
|
match mpls experimental topmost value |
When multiple labels are in use, this command matches the MPLS EXP field in the topmost label. |
|
match not match-criteria |
Reverses the matching logic; in other words, things matched by the matching criteria do not match the class map. |
|
match packet length {max maximum-length-value [min minimum-length-value] | min minimum-length-value [max maximum-length-value]} |
Matches packets based on the minimum length, maximum length, or both. |
|
match protocol citrix app application-name-string |
Matches NBAR Citrix applications. |
|
match protocol http [url url-string | host hostname- string | mime MIME-type] |
Matches a host name and URL string. |
|
match protocol protocol-name |
Matches NBAR protocol types. |
|
match protocol rtp [audio | video | payload-type payload-string] |
Matches RTP audio or video payload, based on the payload type. Also allows explicitly specified payload types. |
|
match qos-group qos-group-value |
Matches a QoS group. |
|
match source-address mac address-destination |
Matches a source MAC address. |
Table 3-11 lists the various MQC subcommands available in Cisco IOS Software for defining actions to be taken.
Table 3-11 Action (PHB) Subcommands Inside a Policy Map
|
Command |
Function |
|
set |
CB Marking action, with options to mark several fields inside headers |
|
bandwidth |
Reserves bandwidth for the class for CBWFQ |
|
priority |
Reserves bandwidth, and provides LLQ with CBWFQ |
|
shape |
Shapes traffic in the class with a defined bandwidth and burst sizes |
|
police |
Polices traffic in the class with a defined bandwidth and burst sizes |
|
compress |
Performs TCP and RTP header compression on packets in the class |
Because routers and switches do different tasks, QoS differs slightly between them, but to get an idea about what AutoQoS does, consider that AutoQoS on routers works to classify packets into three service classes:
Voice payload
Voice signaling
All other traffic
Table 3-12 lists the commands related to AutoQoS VoIP, followed by an example configuration.
Table 3-12 Command Reference for AutoQoS VoIP (for Routers)
|
Command |
Function |
|
auto qos voip [trust] [fr-atm] |
Configuration command that enables AutoQoS VoIP on an interface (PPP or HDLC) or VC (FR and ATM) |
|
no auto qos |
Disables AutoQoS VoIP on an interface (PPP or HDLC) or VC (FR and ATM) |
|
show auto qos [interface interface-type] |
Displays what AutoQoS actually created |
|
show policy-map interface interface-name [input | output] |
Displays actual configuration of MQC-based parts of the configuration, including any later changes made by an engineer |
Table 3-13 shows the PHBs that can be configured by AutoQoS VoIP on a router and some comments about its choices.
Table 3-13 PHBs Generated by AutoQoS VoIP Configuration (for Routers)
|
PHB |
Comments |
|
Class and Mark |
If the trust parameter is omitted, AutoQoS VoIP configures CB Marking, using NBAR, to classify traffic into voice payload (marked DSCP EF), voice signaling (marked DSCP AF31), and all else (marked DSCP BE). |
|
Queuing |
Voice payload is placed into an LLQ. Voice signaling is in another queue with a low-bandwidth CBWFQ queue. All other traffic defaults into the class-default queue, which by default gets 25 percent of link bandwidth. |
|
Compression |
If the link has a bandwidth of 768 kbps or less, cRTP is enabled. |
|
LFI |
If the link has a bandwidth of 768 kbps or less, AutoQoS enables LFI. For interfaces originally configured for HDLC or PPP, AutoQoS reconfigures MLP with LFI on those interfaces. For Frame Relay, AutoQoS configures FR Fragmentation, unless the fr-atm option is configured on the auto qos command. In that case, AutoQoS configures MLP over Frame Relay LFI. In each case, the fragment size is tuned for a 10-ms fragment. |
|
Shaping |
On Frame Relay interfaces, FRTS is configured, tuned for a Shaping interval of 10 ms. |
Cisco IOS switches use the same interface subcommand as routers, but with a couple of different options. The full syntax is as follows:
auto qos voip {cisco-phone | trust}
Figure 3-8 shows the locations where the cisco-phone and trust options should be used, along with some notes about how the cisco-phone option works.
)
Figure
3-8 Two Settings, Three Actions, for Classification and Marking
The list of PHBs created by AutoQoS VoIP differs from routers and is summarized in Table 3-14.
Table 3-14 PHBs Generated by AutoQoS VoIP Configuration (for 2950 EI Switches)
|
PHB |
Comments |
|
Class and Mark |
Classifies based on CoS on trusted ports, or on cisco-phone ports on which an actual phone is attached. Assumes CoS 0 on ports with cisco-phone configured when no phone is detected with CDP 2.0. Re-marks DSCP of packets based on CoS (CoS 5 – DSCP EF, CoS 3 – DSCP AF31, CoS 0 – DSCP BE). |
|
Queuing |
Creates an LLQ for voice payload (CoS 5), and assigns 20 percent of remaining bandwidth to voice signaling (CoS 3), and 80 percent to all other (CoS 0) traffic. |
Table 3-15 lists the four competing options for AutoQoS settings on each port when configuring AutoQoS on Cat-OS. The QoS course includes a wonderful table comparing these three options, included here as Table 3-16, summarizing the comparison points between the three options.
Table 3-15 Comparing Options for set port Command with AutoQoS
|
Command |
Function |
|
trust cos |
Accept the CoS of incoming frames. |
|
trust dscp |
Accept the DSCP of incoming packets. |
|
voip ciscoipphone |
Use CDPv2 to discover the absence or presence of an IP Phone. If one is there, trust CoS, and extend the trust boundary to the IP Phone, causing the PC's frames to be marked CoS 0. If no phone is there, treat all incoming frames as CoS 0. |
|
voip ciscosoftphone |
Trust DSCP, but police DSCP EF at 320 kbps and DSCP AF31 at 32 kbps. |
Table 3-16 Comparisons of CLI, MQC, and AutoQoS
|
|
CLI |
MQC |
AutoQoS |
|
Ease of Use |
Poor |
Easier |
Simple |
|
Ability to Fine Tune |
OK |
Very Good |
Very Good |
|
Time to Implement |
Longest |
Average |
Shortest |
|
Modularity |
Poor |
Excellent |
Excellent |