i want to quantify the latency in my network, as part of an effort to determine whether or not we can deploy a new application
so i've grabbed my Finisar THG box (a hardware packet sniffer with an internal clock accurate to 20ns), a stack of various switches, and some cables. i plug the two ports of the THG box into a switch, send 1,000 pings at a specified internval from one THG NIC through the switch to the other THG NIC, subtract the packet insertion time, average the resulting pile of numbers, and come up with a figure for the forwarding latency (aka decision time) of the device. see my results below. [acknowledgement: work performed by the staff of Network Protocol Specialists]
now i want a sanity check. Cisco must perform this same test (possibly with fancier hardware, like SmartBits boxes) routinely on their gear ... where do they post these results? i've been poking around
for interest, here are my numbers:
Catalyst 4003 100BaseT ports: 3170ns Catalyst 4003 1000BaseSX ports: 705ns [same forwarding latency for 64 byte and for 1518 byte packets]
Cat 4503 1000BaseSX 64 byte: 3300ns Cat 4503 1000BaseSX 1518 byte: 7120ns [why the change in forwarding latency depending on packet size? remember, i've already subtracted packet insertion time]
Cat 6506 1000BaseSX 64 byte: 5000ns Cat 6506 1000BaseSx 1518 byte: 7120ns
Datacomm Aggregration tap 100Mb: 320ns In-Line Finisar 100Mb tap: 0ns NetGear 100Mb hub: 330ns
and finally, we ran a test across our production network (which translates into two access-layer Cat 4506s, two distribution layer Cat
6506s, one core layer Cat 6506, plus ~500m of cabling ... and came out with ~20us of latency, exclusive of packet insertion time. good stuff-where does Cisco post the numbers they have recorded?
-has anyone else performed these kinds of measurements? i'm wanting a conversation about what drives fowarding latency in different Catalyst models ... why, for instance, different packet sizes change decision time, in some models but not in others? what techniques and tools have you used to perform these measurements?
i'm wanting both a sanity check and a deeper understanding
--sk
stuart kendrick fhcrc