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TOS and DSCP resolving

 

Information

 

Summary:

Description of TOS and DSCP mapping for flow field "TOS".

Environment:

Product: FOS

Version: Any

Platform: Any

Question/Problem Description:

What is the meaning of TOS flow field value? How are resolved strings mapped for the ToS header value?

Steps to Reproduce:  
Error Message:  
Defect Number:  
Enhancement Number:  
Cause:  
Resolution: Several networks offer service precedence, which somehow treats high precedence traffic as more important than other traffic (generally by accepting only traffic above a certain precedence at time of high load).

Flowmon converts a decimal value to binary string and maps first 7 bits values according to:

First 3 bits:
['000'] = 'Routine';
['001'] = 'Priority';
['010'] = 'Immediate';
['011'] = 'Flash';
['100'] = 'Flash Override';
['101'] = 'Critical';
['110'] = 'Internetwork Control';
['111'] = 'Network Control';

4 bit
['0'] = 'ND';
['1'] = 'LD';
5 bit
['0'] = 'NT';
['1'] = 'HT';
6 bit
['0'] = 'NR';
['1'] = 'HR';
7 bit
['0'] = null;
['1'] = 'MMC';

DiffServ uses a 6-bit differentiated services code point (DSCP) in the 8-bit differentiated services field (DS field) in the IP header for packet classification purposes. The DS field replaces the outdated IPv4 TOS field. Flowmon also maps these values according to:

ToS DSCP
0 | 0 => 'Best Effort & Default',
40 | 10 => 'AF11',
48 | 12 => 'AF12',
56 | 14 => 'AF13',
72 | 18 => 'AF21',
80 | 20 => 'AF22',
88 | 22 => 'AF23',
104 | 26 => 'AF31',
112 | 28 => 'AF32',
120 | 30 => 'AF33',
136 | 34 => 'AF41',
144 | 36 => 'AF42',
152 | 38 => 'AF43',
32 | 8 => 'CS1',
64 | 16 => 'CS2',
96 | 24 => 'CS3',
128 | 32 => 'CS4',
160 | 40 => 'CS5',
192 | 48 => 'CS6',
224 | 56 => 'CS7',
184 | 46 => 'High Priority & Expedited Forwarding',
Workaround:  
Notes: RFC791, RFC2474, RFC2597, RFC3260, RFC4594 

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