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Arista 7300-series switches cannot perform linerate forwarding of 40-byte TCP SYN packets

"Would this 'discovery' stop me from recommending Arista 7300-series switches in average data center environments? Of course not."

Hummelstown, PA:   Tue, 6/3/14 - 9:29am    View comments

Update 6/18/2014:

CiscoCisco Nexus 9000 Series NX-OS Release Notes

"In OSM, the NFE cannot run at line rate for packet sizes of less than 200 bytes."

Update 6/5/2014 - 11:54am:

Official Response from Arista Networks

Douglas Gourlay - Vice President Systems Engineering:

Douglas GourlayArista NetworksThe 7300 Series was designed to provide wirespeed bandwidth for the most common workloads in the data center, the cloud, and on the Internet - where according to Cisco Systems research the average packet size is between 500-bytes and 600-bytes nowadays, confirmed by a recent post from Greg Ferro here. While there is always some amount of 64-byte frames based on ACKs and SYNs and such during session setup they do not appear as 100% of the traffic in any real world operating environment.

If a customer does need 64-byte frame forwarding at wirespeed, on all interfaces, perfectly meshed, 100% of the time we do offer our 7500 Series which also has larger buffer pools to handle the periods of incast based congestion that are highly likely in that type of contrived test workload.

As Ivan and Brad have both identified - the scenario where 64-byte wirespeed frame forwarding on all interfaces concurrently comes up is in test labs and benchmarking suites. Arista felt that because we already offer a switching family (Arista 7500) that can support this lab benchmark we needed to optimize on supporting our customers requirements for lower power, increased efficiency, and increased port density rather than chasing a benchmark that is useless in the real world.


Arista NetworksIvan PepelnjakLast week CCIE #1354 Emeritus, Ivan Pepelnjak , revealed:

"Arista 7300-series switches cannot perform linerate forwarding of 40-byte TCP SYN packets.

"Is this relevant?

"You might have an environment in which thousands of servers have nothing better to do than saturate 10GE uplinks sending 64-byte VoIP packets or test each other's readiness by sending continuous streams of TCP SYN/RST packets.

"The only environment I'm aware of that comes close to that are the test labs."

Arista 7300 Series

Pepelnjak continued:

"The specifications for their 7300 series switches are pretty clear: a switch with four linecards (512 10GE ports) has 10Tbps switching capacity and can forward 7.5 billion packets per second. The minimum packet size at which they can do linerate forwarding is thus ~160 bytes (around ~150 bytes of L2 payload due to FCS and inter-frame gap).

"I recently spoke with someone who told me their caching servers (a typical example of an environment with small packet sizes) cannot saturate 10GE uplinks due to bottlenecks in Linux TCP stack.

"It's nice to know the actual limitations of each platform you're considering. If you're dealing with unusual workload, make sure to check PPS as well as bandwidth figures (and anything else you might find relevant – for example multicast forwarding performance or ARP table sizes).

"Would this 'discovery' stop me from recommending Arista 7300-series switches in average data center environments? Of course not."

View the website of CCIE #1354 Emeritus Ivan Pepelnjak:


Related documents:

Cisco Nexus 9000 Series NX-OS Release Notes, Release 6.1(2)I2(2a)

Arista 7300 Series

Related story:

CCIE #1354 Emeritus Ivan Pepelnjak: How Line-rate Is Line-rate?

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