Filtering Based on DSCP and TOS

Problem

You want to filter based on IP Quality of Service information.

Solution

You can filter packets based on the contents of the Differentiated Services Control Point (DSCP) field by using the dscp keyword:

Router1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router1(config)#access-list 162 permit ip any any dscp af11
Router1(config)#end

Similarly, to filter based on TOS, you can use the tos keyword:

Router1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router1(config)#access-list 162 permit ip any any tos max-reliability
Router1(config)#end

 

Discussion

In Chapter 11 and Appendix B, we discuss both the DSCP and IP TOS fields in more detail. Chapter 11 also includes several examples of ACLs that filter based on this information. Please refer to these sections for more information.

The first example looks for packets that have a DSCP field value of AF11, which has a bit pattern of 001010, or a decimal value of 10. The second example matches packets with a TOS value of maximum reliability, which has a decimal value of 2.

Note that you can use the decimal numerical values for any TOS or DSCP field, and the router will simply replace it with the mnemonic keyword, if one exists. For example, we could have written the second example as follows:

Router1(config)#access-list 162 permit ip any any tos 2

In this case, the router would have replaced the number 2 with the max-reliability keyword. However, there is no mnemonic keyword corresponding to the TOS value, 3. The router will accept values that do not have well-known names like this, but it will leave them as numerical values in the configuration file.

See Also

Chapter 11; Appendix B

Router Configuration and File Management

Router Management

User Access and Privilege Levels

TACACS+

IP Routing

RIP

EIGRP

OSPF

BGP

Frame Relay

Handling Queuing and Congestion

Tunnels and VPNs

Dial Backup

NTP and Time

DLSw

Router Interfaces and Media

Simple Network Management Protocol

Logging

Access-Lists

DHCP

NAT

First Hop Redundancy Protocols

IP Multicast

IP Mobility

IPv6

MPLS

Security

Appendix 1. External Software Packages

Appendix 2. IP Precedence, TOS, and DSCP Classifications

Index

show all menu





Cisco IOS Cookbook
Cisco IOS Cookbook (Cookbooks (OReilly))
ISBN: 0596527225
EAN: 2147483647
Year: 2004
Pages: 505
Similar book on Amazon

Flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net