Hi all, at work I'm (well, *we* are) facing an interesting problem. Since we are sort of stabbing in the dark here, I thought I'd ask here. Also, since this is from work, I will not be able to diverge very many details (not to mention that as a student worker I simply don't *know* many details). However, I do have permission from my boss to ask about this in an anonymised fashion.
The symptom we're seeing is that the NIC goes down and DHCP packets stop getting through after a certain amount of time. What happens is: 1.) The NIC is brought up (some built-in Intel model). 2.) A DHCP client configures it. 3.) The network connection is lost at some point (the amount of time this takes varies, but it can be as little as 20 minutes). 4.) Eventually the lease runs out and the DHCP client tries to renew it, but gets no response. Sometimes, after many hours (at least 6), it will get a DHCPACK, but that's it. One of our sysadmins says that not only does the DHCP server never see the packets, but the managed switch that the PC is directly attached to *also* never does (again, except for when the occasional DHCPACK comes). 4.) Restart the network device. A reboot is not required, but it is necessary to terminate the DHCP client. After that everything works again. 5.) GOTO 3. (Note that I have observed that steps 3 and 4 do not necessarily occur in order.) This has been rather baffling, since this problem is limited to 3 computers. One of them (the longest running) runs Gentoo, courtesy of me. This is the first one we saw the problem with. Since we couldn't figure it out (switching from dhcpcd to dhclient, turning off the firewall, monitoring with tcpdump, etc., all with help from one of our sysadmins; Google, too, of course), Gentoo was "blamed", so we got a replacement PC with Fedora 20 on it, which *also* showed this behaviour. Both PCs run some special software (some of it mine). Thus, at some point this software was "blamed". So we started experimenting: we configured the Fedora PC to *not* start the special software, and have not seen any problems all week. Yesterday afternoon I then started *one* of the programs, and had not seen any problems yet by the time I went home. So that would speak *for* that theory, right? Well, for comparison, my boss recently started running a separate PC, also with a bog-standard Fedora 20. Guess what: it *also* shows the *exact* same behaviour as the other two PCs ("journalctl -u NetworkManager" shows pages upon pages of unanswered DHCPREQUESTs, with the occasional response thrown in). Note here that this PC is on a different switch and in a different VLAN. The choice of Fedora comes from the fact that we use a Fedora based distro internally, so it is "known". PCs running it have *not* shown the behaviour above (AFAIK not even *once*). Thus, one of the few things I can think of is finding out what is different about them relative to the standard Fedora. Right now my main ideas on what the culprit could be are: - The computers' kernel/network device is improperly configured. That is, maybe special configuration is needed for the computers to work properly as clients in the network. I'm thinking of support for some (from my perspective) obscure protocol(s). - It's a network problem. The three computers are in two different VLANs, while the workplace computers running the internal Fedora based distro are in a third (the main network that all the normal Windows and Linux workstations are connected to). However, they are on the same switch as the two computers running my software. One argument against this is that the Windows PC that runs on the same VLAN does *not* have any problems like this. One of the other ideas I had was faulty power management, and I did read of problems of the sort regarding the exact same network card that is in the old Gentoo machine on an HP support forum (from around 2008). However, the local sysadmin said that they have had nothing but good experience with those network cards. Also: *three* computers with NIC power management problems? That sounds a bit far-fetched to me. Nevertheless, I am not fully discounting the possibility. You can imagine how confusing and frustrating this is. So, has anybody here ever experienced something like this? Any ideas on what could be the cause? Greetings -- Marc Joliet -- "People who think they know everything really annoy those of us who know we don't" - Bjarne Stroustrup
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