I need some education from you knowledgeable folks in the world of networking.

What does NAT Throughput mean?

Example: I'm looking to install a multi-WAN router in a location that can only get a few slow connections (but they want to support a large number of users). They're looking to get a few cable modems in order to accomodate the load of all those users.

First, I know that if I have three 10Mbps connections, that doesn't mean one computer could get 30Mbps. It would get 10Mbps. However I assume three computers would all get 10Mbps in this scenario.

What I'm trying to do is figure out a spec on the router that was ordered. The router claims it has an 80Mbps NAT Throughput. What I'm trying to do now is advise the property owner about what he should order from the cable company. Am I correct in assuming that if he pays extra for the 100Mbps connections they offer, it would be a waste of money? Does this just mean that if a single PC were on the network, it would get 80Mbps, but two PCs would get 50 each? Or does this mean that the router can only distribute 80Mbps to the network in total?

Thanks for your wise counsel

It should mean that if they get the 100Mbps service, 20% will not be usable. You're assuming the 100Mbps will actually be fully available. I'm not sure the difference is enough to worry about in that case. The 80Mbps will be a total figure. So two machines will be 40Mbps each in your example.

Think of it like this. Say the WAN was 1000Mbps, and you had 20 machines - they're not going to get 50Mbps each. The router can't scale up like that.

Also if you have 3 cable modems you'll need a router that supports three WANs which may be a higher model. 80Mbps seems a little slow particularly for something that might be able to handle 3 WAN interfaces.

What are you looking at?

This is the device they ordered.

My apologies, but I'm still confused. So if the NAT throughput is 80Mbps, and I have a few cable modems all providing (theoretically) 100Mbps of service, and I only losing 60Mbps (which might be livable) or 220Mbps, making two of those modems completely useless?

The throughput the router can deliver, from external side to internal computers (and vice-versa), is a total of 80mbit/sec. Or less if more stuff in the router is enabled.

The reason they quote "NAT" thoughput, is that "NAT" requires software (CPU) involvement on the router for each and every packet passing from internal to external and vice-versa, so communication speed is dependent upon the speed of the processor inside the router.

LAN speed on the router, say from one PC to another, is unaffected, as the packets there are switched directly by hardware, at full wire speed (100mbit/sec). No software involved.

"NAT" (Network Address Translation) is the core feature of most firewalls, enabling many internal PCs to share a single (or a few) external IP address. By itself, it is often adequate. Most firewalls also do "SPI" (Stateful Packet Inspection), which simply means the embedded Linux kernel is trying to block a lot of protocol violations in addition to doing NAT. And SPI can get a lot fancier, depending upon the features enabled.

But using SPI takes more CPU horsepower inside the router, and will probably lower the maximum NAT throughput.

The only way to really know if it's "good enough", is to try it and measure it.

Cheers

User Manual -- no mention of performance specs.

Datasheet -- mentions the 80mbit/sec limitation.

So.. yeah, this router is unlikely to do a great job of amalgamating more than a total of 80mbit/sec of internet-side bandwidth. Dunno if that's 40mbit/sec in and 40mbit/sec out, or what though.

Gotta love vague specifications.

Given that the CPU inside is clocked at only 170MHz, it is unlikely to be a higher performance product. They could have some hardware assistance built-in for NAT and the like to compensate, but this thing is lower spec than many newer home routers.

Interesting that notes on the manufacturer's web site indicate " the maximum bandwidth the SW88 will manage is 51200 K bit/sec" (51mbit/sec, not 80mbit/sec).

This thing looks fantastic for load-balancing across multiple DSL links or other tech from a few years ago. But it'll be a choke point for cable internet or FIOS.

-ml

Thanks for your input, Mark. I was afraid this was what you would say.

It's something I should have made sure of, but frankly it's also something that should be better presented. There's absolutely nothing on the Amazon page that mentions that 80Mbps limit, and given the speeds that providers are offering these days, I don't think it's unreasonable to expect better performance.

But I'm also at fault. Now I know about this issue, and I'll design around it. It looks like I'm going to have to split this building up into a few different networks, one on each modem (they're also crappy routers, of course). They don't need to talk to each other at all, so it's not a big deal...

By the way, what are the chances that one of the cable company's own modem/router combos have a throughput of the whole 100Mbps?

And this makes that 300Mbps Fios service even more impressive (I have to assume it can deliver that to the network). Too bad it's not in the area.

The modems for Cable (DOCSIS 3.0) can deliver 2-3X that speed, no problem. But modem/router combos will depend upon the CPU horsepower in the router. I imagine that most newer gigabit routers can handle 100mbit/sec with NAT, and I especially expect that a combo Cable modem/router can handle it.

Edit: The two cable modems I have here are each capable of 340-440 mbits/sec downstream performance (plus 120mbits/sec upstream), but neither has a built-in router. It's the router part that tends to be a choke point, because of the software (CPU) intervention required per-packet.

Cheers