I think it would be interesting to put a table of routing devices together along with the commands it takes to knock down their forwarding rates. And to find out what platform has the higher percentage drop in forwarding rate. As mentioned elsewhere, it's not the pps, but operations per second. Frank -----Original Message----- From: David Newman [mailto:dnewman@networktest.com] Sent: Sunday, September 07, 2008 9:23 AM To: nanog@nanog.org Subject: Re: Force10 Gear Paul Wall wrote:
Once upon a time, vendors released products which relied on CPU-based "flow" setup. Certain vintages of Cisco, Extreme, Foundry, Riverstone, etc come to mind. These could forward at "line rate" under normal conditions. Sufficient randomization on the sources and/or destinations (DDoS, Windows worm, portscans, ...) and they'd die a spectacular death. Nowadays, this is less of a concern, as the higher-end boxes can program a full routing table (and then some) worth of prefixes in CAM.
Either way, I think it's a good test metric. I'd be interested in hearing of why you think that's not the case. Back on topic, doing a couple of gigs of traffic at line rate is a walk in the park for any modern product billed as a "layer 3 switch". The differentiator between, say, a Dell and a Cisco, is in the software and profoundly not the forwarding performance.
Without disagreeing with your main point, there are still plenty of ways to bring even very large boxes to near-zero forwarding rates: 1. Set IP options. A pair of Cat 6509Es using VSS can forward packets without options at up to 770 mpps, but when packets have options the maximum is more like 20 kpps. And that's a "high-speed" example; the options forwarding rate is more like 0 pps with some other devices. Silicon that forwards packets very fast is only good when header lengths are fixed. 2. Use weak hashing algorithms. Some switches (names removed to protect the guilty) hash on the low-order three bits of MAC address to decide which of eight ASICs will forward a packet. I have heard of, but have not tested, devices that use only three bits for making OSPF ECMP decisions. Not surprisingly either technique can lead to lots of hash collisions in routed environments. 3. Offer IP multicast. Maximum forwarding rates for multicast are rather different than IP unicast with some vendors' implementations, and may be affected by group count, mroute count and amount of replication. dn