[Bloat] ToS bits being set to mitigate transit congestion problems

Justin McCann jneilm at gmail.com
Thu Nov 6 12:47:28 EST 2014

The m-labs discussion list has had some traffic lately trying to figure out
why NDT throughput changed abruptly.

Apparently Cogent (and others?) has started setting ToS bits on retail
customer traffic, and leaving wholesale traffic as-is (see below).


Observed ToS settings include 0x00, 0x28, and 0x48:


Nice to see at least some network operators talking about what they're


Due to the severe level of congestion, the lack of movement in negotiating
possible remedies and the extreme level of impact to small enterprise
customers (retail customers), Cogent implemented a QoS structure that
impacts interconnections during the time they are congested in February and
March of 2014.  Consistent with recommendations from BITAG (Broadband
Internet Technical Advisory Group:
Cogent prioritized based on user type putting its retail customers in one
group and wholesale in another.  Retail customers were favored because they
tend to use applications, such as VoIP, that are most sensitive to
congestion.  M-Labs is set up in Cogent’s system as a retail customer and
their traffic was marked and handled exactly the same as all other retail
customers.  Additionally, all wholesale customers traffic was marked and
handled the same way as other wholesale customers.  This was a last resort
effort to help manage the congestion and its impact to our customers.

Hank Kilmer
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