Ray Olszewski wrote:
Hmm...I'll jump in here with a brief comment. This behavior *DOES* sound a lot like what I've seen happen when dramatically over-saturating the upstream link. I hadn't thought about this solution before, since bandwidth usage (via MRTG) is the first thing I check when getting reports of "sluggish" or otherwise broken internet connections.I never suggested a hardware problem; other tests you reported pretty much ruled that out. But remember that your Ethernet connection between the router and the ZyXEL is almost surely fast, either 10 Mbps or 100 Mpbs, while your connection from the ZyXEL to the Internet is slow (on the order of 1 Mbps, probably, though you haven't actually told us). A LAN or router problem could easily saturate the Internet connection but leave plenty of room on the router-ZyXEL link to permit it to handle ping traffic quickly. The symptoms you report are quite consistent with this interpretation.Note: pings from the router box to the ZyXEL modem itself, i.e. "first hop" pings, are in the 2-4 ms range. That certainly doesn't sound like a hardware problem with the ethernet cards to me. It seems to happen only when you go out beyond the modem into the external network at large.
Typical bandwidth hogs (on my networks) are compromisied systems, e-mail "blasts" from the marketing folks (trying to send to 10,000+ end-users over a T-1 during mid-day peak usage times), and peer-peer packages like kazza. The biggest cuplrit by far is hacked windows boxes, which typically try to connect to everything they can to spread the infection (I don't have control over several windows-based servers tied to the 'net, and they're *ALWAYS* getting compromisied...all I can do is shut them down until they're cleaned up :< ).
In all these situations, normal TCP/IP slow-start bandwidth throttling can fail, due to the sheer number of connections generated. With the outbound pipe saturated, packet latencies and packet loss both increase dramatically, to numbers typical of what you reported.
A system that has recently been infected, or perhaps a recent installation of peer-peer software somewhere could also easily explain why a functioning network might suddenly stop working properly.
I'd check your internal systems and make sure no machines are compromisied.
--
Charles Steinkuehler
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