QOS with a hint of PBR at the beginning :)

Policy Based Routing

First off Policy Based Routing aka PBR (not pabst blue ribbon ;) is used to make sure traffic is forwarded to the destination we set it to go.

To identify the Route Map used for policy routing we use the command:
router#ip policy route-map Map_Name

We build our route maps by matching traffic based on:

• Access List- protocol or application
• Access List- particular source and/or destination
• Layer 3 packet length

Whenever traffic does not match an ACL we typically set the behavior of where we want the traffic to go. We also set the behavior for matches to the ACL as well.

We set the behavior by:

• Next hop
• Output interface
• Default next hop
• Default interface

Module Quality of Service CLI (MQC)

MQC was originally invented for CBWFQ

There are three steps to configure MQC
1) Identify traffic "buckets"
"class-map"
2) Dictate policy-what happens to the traffic?
"policy-map"
3) Assign the configuration
"service-policy"

Network Based Application Recognition aka NBAR

NBAR has two jobs

• Protocol analysis
• Traffic classification for QOS

Packet Description Language Modules (PDLMs)

Deep packet inspection

Protocol Discover

• "ip nbar protocol-discovery"
• "show ip bar protocol-discovery"

Marking

Marking options

• Layer 2 and layer 3 options exist
• Remarking/translating is often needed
• CoS, IP Precedence, DSCP, MPLS, Experimental Bits, DE, FECN/BECN

Layer 2 Class of Service

• 802.1P
• 3 bits of the 802.1Q tag used for marking

___CoS______Bits_____Application
7 111 Reserved (network)
6 110 Reserved (internet)
5 101 Voice Bearer (critical)
4 100 Video (flash-override)
3 011 Call signaling (Flash)
2 010 High Priority Data (immediate)
1 001 Medium Priority Data (priority)
0 000 Best Effort (routine)

Layer 2 Frame Relay

• Packet discard during congestion
• Discard eligibility bit (DE)
• This feature works in conjunction with FECNs and BECNs

Layer 2 ATM

The Cell Loss Priority field (CLP) pretty much the same as the DE in frame relay
1 bit to indicate drop priority


Layer 2 MPLS Experimental Bits

• Layer 2 1/2
• 3 Bits that can be used for QoS
• By default, first (high order) bits of the Layer 3 ToS field are copied here (IP Precedence)

Layer 3 Many Uses for the ToS Byte

• 8 bit ToS field in the IP Header
• First 3 bits used for IP Precedence
• Expanded to use first 6 bits for Differentiated Services Code Point(DSCP)
• Last two bits are used for Flow Control

DSCP

• Standardized markings using the first six bits of the ToS byte
• Markings are standardized into published PHBs (Per Hob Behaviors)

DSCP PHBs

Class Selector (CS) PHB

• Used for pure backward compatibility with IP Precedence
• Last three bits set to 000

Default PHB

• Best effort service (000000)

DSCP PHBs

Assured Forwarding (AF) PHB

• Guaranteed bandwidth services
• 001,010,011, or 100 initial bit settings

Expedited Forwarding (EF) PHB

• Used for voice
• First three bits 101

QoS Policy Propagation through BGP QPPB

Classify packets based on:

• Access lists
• BGP community lists
• BGP AS Paths
• Specific BGP attributes can be assigned to packets based on ToS markings