Generate DSCP marked pings

Today it was useful to confirm a switch was passing DSCP marked packets as expected and handling ‘ef’ marked packets.

To do this on a cisco switch we can use the extended ping feature and set the Type of Service (ToS) to a decimal value that is equivalent to the DSCP value wanted. The table below shows the ToS value to enter to get the DSCP marking needed.

TOS (decimal) DSCP Class
0 be
32 cs1
40 af11
48 af12
56 af13
64 cs2
72 af21
80 af22
88 af23
96 cs3
104 af31
112 af32
120 af33
128 cs4
136 af41
144 af42
152 af43
160 cs5
184 ef
192 cs6

So for example if we want to generate EF marked packets we can use the value of 184 for ToS when configuring the extended ping. Obviously any other marking like af43 = 152 can easily be used too.

On a Cisco switch extended ping example below:

Protocol [ip]: 
Target IP address:
Repeat count [5]: 100
Datagram size [100]: 
Timeout in seconds [2]: 
Extended commands [n]: y
Source address or interface: 
Type of service [0]: 184 <---------THIS SETS THE QOS MARKING
Set DF bit in IP header? [no]: 
Validate reply data? [no]: 
Data pattern [0xABCD]: rotate
Loose, Strict, Record, Timestamp, Verbose[none]: 
Sweep range of sizes [n]: 
Type escape sequence to abort.
Sending 100, 100-byte ICMP Echos to, timeout is 2 seconds:
Packet has rotating data pattern starting with 0x0000
Success rate is 100 percent (100/100), round-trip min/avg/max = 60/63/64 ms

Nice hacky way to generate ef marked traffic for testing 🙂

More info about DSCP values in relation to other values can be found [HERE].


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