jm + ethernet   6

Linux kernel bug delivers corrupt TCP/IP data to Mesos, Kubernetes, Docker containers — Vijay Pandurangan
Bug in the "veth" driver skips TCP checksums. Reminder: app-level checksums are important
checksums  tcp  veth  ethernet  drivers  linux  kernel  bugs  docker 
april 2016 by jm
How both TCP and Ethernet checksums fail
At Twitter, a team had a unusual failure where corrupt data ended up in memcache. The root cause appears to have been a switch that was corrupting packets. Most packets were being dropped and the throughput was much lower than normal, but some were still making it through. The hypothesis is that occasionally the corrupt packets had valid TCP and Ethernet checksums. One "lucky" packet stored corrupt data in memcache. Even after the switch was replaced, the errors continued until the cache was cleared.

YA occurrence of this bug. When it happens, it tends to _really_ screw things up, because it's so rare -- we had monitoring for this in Amazon, and when it occurred, it overwhelmingly occurred due to host-level kernel/libc/RAM issues rather than stuff in the network. Amazon design principles were to add app-level checksumming throughout, which of course catches the lot.
networking  tcp  ip  twitter  ethernet  checksums  packets  memcached 
october 2015 by jm
Nelson recommends Ubiquiti
'The key thing about Ubiquiti gear is the high quality radios and antennas. It just seems much more reliable than most consumer WiFi gear. Their airOS firmware is good too, it’s a bit complicated to set up but very capable and flexible. And in addition to normal 802.11n or 802.11ac they also have an optional proprietary TDMA protocol called airMax that’s designed for serving several long haul links from a single basestation. They’re mostly marketing to business customers but the equipment is sold retail and well documented for ordinary nerds to figure out.'
ubiquiti  wifi  wireless  802.11  via:nelson  ethernet  networking  prosumer  hardware  wan 
september 2015 by jm
TCP incast
a catastrophic TCP throughput collapse that occurs as the number of storage servers sending data to a client increases past the ability of an Ethernet switch to buffer packets. In a clustered file system, for example, a client application requests a data block striped across several storage servers, issuing the next data block request only when all servers have responded with their portion (Figure 1). This synchronized request workload can result in packets overfilling the buffers on the client's port on the switch, resulting in many losses. Under severe packet loss, TCP can experience a timeout that lasts a minimum of 200ms, determined by the TCP minimum retransmission timeout (RTOmin).
incast  networking  performance  tcp  bandwidth  buffering  switch  ethernet  capacity 
november 2014 by jm
Directv DCA2SR0 01 Deca II Connected Home Adapter
a John-Looney-recommended MoCA adapter, allowing legacy coax home wiring to be used to transmit ethernet
ethernet  coax  legacy  wiring  home-networking  moca  directv 
january 2014 by jm
Groundbreaking Results for High Performance Trading with FPGA and x86 Technologies
The enhancement in performance was achieved by providing a fast-path where trades are executed directly by the FPGA under the control of trigger rules processed by the x86 based functions. The latency is reduced further by two additional techniques in the FPGA – inline parsing and pre-emption. As market data enters the switch, the Ethernet frame is parsed serially as bits arrive, allowing partial information to be extracted and matched before the whole frame has been received. Then, instead of waiting until the end of a potential triggering input packet, pre-emption is used to start sending the overhead part of a response which contains the Ethernet, IP, TCP and FIX headers. This allows completion of an outgoing order almost immediately after the end of the triggering market feed packet.

Insane stuff. (Via Martin Thompson)
via:martin-thompson  insane  speed  low-latency  fpga  fast-path  trading  stock-markets  performance  optimization  ethernet 
october 2013 by jm

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