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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Routers vs. PC's for routing - was list problems?
At 02:20 PM 5/23/2002 -0400, you wrote: I'm assuming you meant RAID-1. In RAID-0 if you 'swapped' any drive all your striped data is toast. ;)Vinny Abello wrote: > > I would have to say for any Linux/BSD platform to be a viable > routing solution, you have to eliminate all moving parts or as much > as possible, ie. no hard drives because hard drives will fail. Not > much you can do about the cooling fans in various parts of the > machine though which routers also tend to have. Solid state > storage would be the way to go as far as what the OS is installed > on. You have to have something to imitate flash on the common > router. Otherwise, if you can get the functionality out of a PC, > I say go for it! The processing power of a modern PC is far beyond > any router I can think of. I suppose it would just be a matter of > how efficient your kernel, TCP/IP stack and routing daemon would > be at that point. :) I've several comments here. First off, you're right about moving parts generally being a bad thing. However, it is not always necessary to eliminate the hard drive. Two drives in a RAID-0 configuration may be reliable enough. Especially if the failure of a single drive sets off sufficient alarms so that it can quickly be hot-swapped for a new drive. I agree with you on that. Hot swapability for various interfaces is something routers obviously have over PC's.The real problem with using PCs is bandwidth and hardware reliability. PCs generally don't have many hot-swappable parts. You can get hot-swap hard drive assemblies without too much work, and redundant power supplies can be purchased. A motherboard that allows hot-swapping of PCI cards (usually by having multiple busses and a mechanism to turn them off individually) is very rare. You can get dual-CPU motherboards, but not with the processors being hot swappable. And I don't know if any will allow the system to transparently fail over from one CPU to another, should the primary fail. True... unless going for 64 bit PCI at 66MHz... still it's obvious that routers are designed for one simple purpose and generally have larger backplanes to handle that.Then there's the issue of the PCI bus. Standard PCI (32-bit 33MHz) has a theoretical maximum bandwidth of about 1Gbit/s. But you can never use all of a PCI bus's bandwidth, so actual limits will be less than this. I agree a router is probably more efficient in just routing packets, but in complex filtering or traffic manipulation/packet sniffing, a PC might have the edge. :)When you're doing software routing, every packet must cross the bus twice - once for the receive and once for the send. So your standard PCI bus (if used for nothing but packets) has a top speed of 500Mbit/s. Which is less than three ports of full-duplex fast Ethernet at line rate. Multiple busses and/or 64-bit 66MHz PCI can increase this limit, but now you're talking about much more expensive motherboards. You can dramatically improve throughput if you can get line cards that have on-board forwarding chips. If cards can forward packets between each other without getting the CPU involved, then packets can cross the PCI bus only once. But these kinds of line cards are not cheap, if they can be found at all. And you will need some way of downloading your kernel routing table into the cards, which may require some serious OS hacking. In other words, a PC equipped to be as reliable and capable as a decent router will likely end up costing as much as a router. And the reason has nothing to do with the CPU speed or the operating system. Don't get me wrong. I would never use a PC for a router, just as I wouldn't try to run my workstation as a 7206. ;) It's all just hypothesizing. Vinny Abello Network Engineer Server Management [email protected] (973)300-9211 x 125 (973)940-6125 (Direct) Tellurian Networks - The Ultimate Internet Connection http://www.tellurian.com (888)TELLURIAN
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