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ndemou
Asked: 2018-04-16 01:54:39 +0800 CST

Very strange network behavior (perfect HTTP at 50% ping losses for specific Ethernet card)

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I'm dealing with Ethernet networks since 1989 and I believed I had seen it all when a few days ago I had this really strange experience that first I have to share with someone and second I'd love to get feedback If anybody has seen anything similar or if you can you think of any other troubleshooting trick or workaround I could try.

The issue

I had two different Oxygen ADSL modem/routers to connect to a PC running pfsense(a FreeBSD based firewall/router). The PC had an HP NC364T quad Ethernet Card that I had used time and time again in the past. All seemed good but I then noticed this bizarre behavior: I could browse the Internet without any delay but ping was giving me a 40-50% packet loss no matter from where and to where I was pinging. Pinging the IP of the ADSL modem from the pfsense PC: 40-50% loss. Pinging from any other PC behind pfsense to any Internet host: 40-50% loss. I know that HTTP can withstand some packet loss but at 40 to 50% it should have been at least painfully slow if not totally unusable. And a RDP connection I tried was also snappy!!! It's as if the incompatibility affected only ICMP traffic.

Things I tried that had no effect

I Changed the cable & the card with another one of the same maker/model and then changed both once more (in total I tried 3 different cards and cables all of them where later proven to work just fine in another setup). Changed the settings for the Ethernet speed to 100Mbit/FD on both the modem and the HP Card. The whole time I was testing with either one or the other or both modem models.

Either of these changes was fixing the issue

  1. changing from HP NC364T to cheap LAN cards

  2. changing the modem to a third model -- again Oxygen but not exactly the same model with any of the other two

  3. inserting a switch between the router and the PC.

Epilogue

It seems that these two specific Oxygen models don't want to talk to this specific LAN card model directly. If it was one modem/router model I would have been less surprised but hitting two cases on the same day seems a very strange coincidence. And the bizarre phenomenon of 50% ping losses while at the same time happily browsing at full speed really drives me insane.

ethernet

0 Answers