Differentiated services or DiffServ [RFC2474] is a networking architecture that specifies a simple, scalable and coarse-grained mechanism for classifying and managing network traffic and providing quality of service (QoS) on modern IP networks. DiffServ can, for example, be used to provide low-latency to critical network traffic such as voice or streaming media while providing simple best-effort service to non-critical services such as web traffic or file transfers.
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 The DS field and ECN field replace the outdated IPv4 TOS field. [RFC3260]
The DSCP plugin for PATHspider aims to detect breakage in the Internet due to the use of a non-zero DSCP codepoint.
To use the DSCP plugin, specify
dscp as the plugin to use on the command-line:
pathspider dscp </usr/share/doc/pathspider/examples/webtest.csv >results.txt
This will run two TCP connections for each job input, one with the DSCP set to
zero (best-effort) and one with the DSCP set to 46 (expedited forwarding). If
you would like to specify the code point for use on the experimental flow, you
may do this with the
--codepoint option. For example, to use 42:
pathspider dscp --codepoint 42 </usr/share/doc/pathspider/examples/webtest.csv >results.txt
In addition to the default output fields, the DSCP plugin also provides the following fields for each flow:
|fwd_syn_dscp||DiffServ code point as observed on the forward path for the first SYN in the flow.|
|rev_syn_dscp||DiffServ code point as observed on the reverse path for the first SYN in the flow (likely to be a SYN/ACK).|
|fwd_data_dscp||DiffServ code point as observed on the forward path for the first data packet (i.e. with a payload) in the flow.|
|rev_data_dscp||DiffServ code point as observed on the reverse path for the first data packet (i.e. with a payload) in the flow.|
- DSCP marking is performed using the
config_zerofunction will flush this table. PATHspider makes no guarantees the the configuration state is consistent once it has been set, though you can use the forward path markings in the output to validate the results within a reasonably high level of certainty that everything behaved correctly.