When setting up a basic CB marking, we need to do the following steps:
- We first need to define our access lists (lines 28-32) to find the traffic that we want to classify.
- Next, we need to create a class map that links to an access list (lines 4-7). You could think of this step as naming the access list.
- Now we create the policy map with whatever class maps should be included (lines 10-17), and define how we should mark the traffic
- Finally, we need to bind a policy map to an interface (line 26). Note that you can bind two policy maps to an interface, one inbound, and one out.
Example of Basic CB Marking
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!
ip cef
!
class-map match-all HI
match access-group 101
class-map match-all LO
match access-group 100
!
!
policy-map IPFRCOS
class HI
set ip dscp af31
bandwidth percent 35
class LO
set ip dscp af21
class class-default
set ip dscp default
!
!
interface Serial0/0/0
description description IPFR AT&T Ckt ID:
bandwidth 1536
ip address 10.109.2.81 255.255.255.252
encapsulation frame-relay IETF
frame-relay lmi-type cisco
service-policy output IPFRCOS
!
access-list 101 permit tcp any eq telnet any
access-list 101 permit tcp any any eq telnet
access-list 101 permit icmp any any
access-list 101 permit tcp any any eq 1494
access-list 101 permit udp any any eq 1604
! |
Cisco's Recommended Values for Marking:
| Type of Service |
CoS |
Precedence |
DSCP |
| Voice Payload |
5 |
5 |
EF |
| Video Paylod |
4 |
4 |
AF41 |
| Voice/Video Signaling |
3 |
3 |
AF31 |
| High-priority or gold data classes |
2 |
2 |
AF2x (x=1-3) |
| Medium-priority or silver data |
1 |
1 |
AF1x (x=1-3) |
| All else |
0 |
0 |
Default
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IETF RFCs have defined special keywords, called Per-Hop Behaviors, for specific DSCP markings - EF: Expedited Forwarding (RFC3246)
- CSx: Class Selector (RFC2474)
- Where x corresponds to the IP Precedence value (1–7)
- (DSCP 8, 16, 24, 32, 40, 48, 56)
- AFxy: Assured Forwarding (RFC2597)
- Where x corresponds to the IP Precedence value (only 1–4 are used for AF Classes)
- And y corresponds to the Drop Preference value (either 1 or 2 or 3)
- With the higher values denoting higher likelihood of dropping
- (DSCP 10/12/14, 18/20/22, 26/28/30, 34/36/38)
- BE: Best Effort or Default Marking Value (RFC2474)
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