TCP throughput and duplex mismatch
From GEANT2-JRA1 Wiki
[edit]
Observations
- 2 Mbps were observed from Catania to Frascati -
- About 80 Mbps in the other direction
- The day before, there was around 80Mbps from Catania to Frascati
[edit]
Questions
- Why are we getting only 2Mbps between Catania and Frascati?
- Why are we getting only 80Mbps from Frascati to Catania in general whilst we would expect up to 1Gbps from the MDM service? For question2, please refer to Why_is_the_TCP_throughput_test_around_80-90Mbps?
[edit]
Investigations
- When investigating question2, we discovered that the Catania server is connected to 100Mbps interface, which limits the bandwidth in can use.
- Let's now investigate the question1.
- Looking at the previous days (14/01, 15/01), we found out that the TCP throughput was around 80Mbps and were stable. But on the 15/01, all the measurements after 18:00 dropped to 2Mbps and stayed there.
- To the eyes of a network engineer, that the drop occured after 18:00 indicates that the change might be due to a configuration change. (the network operation centers operate most of the time the configuration changes outside the working hours (i.e. before 09:00 and after 18:00).
- The Service Desk was contacted and reported the issue to the people responsible of the server. After a quick investigation it occured that the there was an interface erroneously configured as half-dulpex on the router interface that sees the switch.
- The configuration was changed after 15:00
