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  • Why Does Wireless Gear Degrade Over Time?

    - by bahamat
    I saw this originally posted on slashdot, but their comment format is not conducive to actually getting a correct answer. Having directly experienced this phenomenon myself, I'm now asking here where I think I can actually get an educated answer. Here's the original question verbatim: Lately I have replaced several home wireless routers because the signal strength has been found to be degraded. These devices, when new (2+ years ago) would cover an entire house. Over the years, the strength seems to decrease to a point where it might only cover one or two rooms. Of the three that I have replaced for friends, I have not found a common brand, age, etc. It just seems that after time, the signal strength decreases. I know that routers are cheap and easy to replace but I'm curious what actually causes this. I would have assumed that the components would either work or not work; we would either have a full signal or have no signal. I am not an electrical engineer and I can't find the answer online so I'm reaching out to you. Can someone explain how a transmitter can slowly go bad? Common (incorrect, but repeated) answers from slashdot include: Back then your neighbors didn't have wifi, now they do. They drowning you out. I don't think this is likely because replacing the access point with a new one and using the same frequencies solves the problem. Older devices had low transmit power. Crank that baby. As mentioned by a FreeBSD wireless developer this violates regulations and can physically damage the equipment. It was also mentioned that higher power in one direction is not necessarily reciprocated. This shows higher bars, but not necessarily a better connection. Manufacturers make cheap crap designed to wear out. This one actually may be legitimate although it is overly broad. What specifically causes damage over time? Heat? Excessive power? So can anyone provide an informed answer on this? Is there any way to fix these older access points?

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  • Ubuntu 12 crashed and took down network

    - by Leopd
    We recently set up a new Ubuntu 12.04LTS server on our network. It's not fully configured so it's not doing much beyond sshd and a default apache2 install. But this evening it appears to have crashed. It wasn't responding to the network or the keyboard. But the worst part is, it took down the entire network. My knowledge of the network stack below OSI layer 3 is very limited, so the rest confuses me. When this machine was physically connected to the network, no other machine could connect to the outside internet. When things were broken, running arp showed that our gateway's IP address (10.0.1.1) was listed as "invalid." Unplugging the server from the network fixed the problem, and plugging it back in broke it again. So the crashed server was advertising itself as owning the gateway's IP address? There's nothing at all in syslog during the time when it was causing problems. Any ideas about how to figure out what went wrong or what we can do to prevent it from happening again? I'm hesitant to even put the machine back on the network right now. Update ** It crashed again, and I ran tcpdump -penn arp (thanks bahamat!) for several minutes and got this... (timestamps and duplicate lines removed) 00:1e:65:f8:dc:24 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 10.0.1.1 tell 10.0.2.191, length 46 00:1e:65:f8:dc:24 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 10.0.1.44 tell 10.0.2.191, length 46 60:d8:19:d4:71:d6 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 10.0.1.1 tell 10.0.2.125, length 46 d4:9a:20:04:e9:78 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 42: Request who-has 192.168.1.1 tell 192.168.1.100, length 28 Update 2 ** When the network is functioning properly, arping -c4 10.0.1.1 returns this: ARPING 10.0.1.1 60 bytes from c0:c1:c0:77:25:8e (10.0.1.1): index=0 time=267.982 usec 60 bytes from c0:c1:c0:77:25:8e (10.0.1.1): index=1 time=422.955 usec 60 bytes from c0:c1:c0:77:25:8e (10.0.1.1): index=2 time=299.215 usec 60 bytes from c0:c1:c0:77:25:8e (10.0.1.1): index=3 time=366.926 usec --- 10.0.1.1 statistics --- 4 packets transmitted, 4 packets received, 0% unanswered (0 extra) When the bad server is plugged in, arping -c4 10.0.1.1 returns: ARPING 10.0.1.1 --- 10.0.1.1 statistics --- 4 packets transmitted, 0 packets received, 100% unanswered (0 extra) Context ** 10.0.x.x is the main subnet. 10.0.1.1 is the main internet gateway 10.0.1.44 is a printer 10.0.2.* devices are all laptops / workstations I have no idea what's using the 192.168.x.x subnet -- your guesses are at least as good as mine. A VM on a workstation? A misconfigured WAP? Somebody re-sharing wifi? A machine that failed to DHCP? The offending ubuntu server's MAC address ends in cd:80 so isn't listed in the dump. It should DHCP to 10.0.3.3 Thanks for any help. This ARP stuff is all voodoo to me. Packets just go to IP addresses, right? ;)

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