Debian Configuration :: WiFi Connects But Can't Ping - No Internet

I've been using Debian for about 6-7 months now. I've had a bit of a major networking problem for the past 4 months or so that I've been trying to fix - specifically, it started when I upgraded to Jessie. I can connect to wifi just fine, and sometimes I can even use the internet for brief periods of time (exceedingly rarely). Then... nothing. No network access, period. I can't ping any outside servers, I can't ping other computers on my network, and I can't even ping my router. Pages I try to load just stay "connecting" for all eternity, network printing fails, and so on.

So after four months of searching online (I've read through way more wireless documentation than I care to say), I finally gave up and admitted that maybe I screwed something up during upgrade to Jessie (as a matter of fact, I did, I had to do the upgrade in two increments [somehow] because my root partition was too tiny by mistake) and I did a clean install. Since I had /home on a separate partition, I was able to keep all my user files, but all settings regarding networking were wiped. So after installing firmware-iwlwifi so I can use my wireless card, I tried connecting to wireless! Success! Then I tried connecting to the internet... success! Briefly. The next morning I tried using the internet again, and it failed in exactly the same pattern as before.

I don't know much about what's going on here, but here's what I do have available:

I do have to use firmware-iwlwifi, which I installed by doing apt-get install firmware-iwlwifi. I don't think it's an issue with the wireless card itself (hardware-wise), the laptop dual-boots Windows 7 (that I never use anymore), and Windows 7 is able to connect to the internet just fine. Connecting directly to my router by ethernet cable works fine, I have perfect internet/network access then.

I can confirm that my laptop is receiving an IP address and that it is using ARP correctly to get the MAC address of my router (I confirmed this by doing the arp command, it has the MAC address correct, I checked from another computer with my router's config page) All other computers on my network work perfectly with my router. To confirm the router/its configuration isn't at fault, I did a full factory reset of the router, but to no avail.

Out of curiosity I tried installing Wireshark (using an ethernet cable to download it) to monitor what happens when I try to access a webpage. I'm no expert on networking, but I noticed something out place when I compare a capture from the affected computer to a capture from one operating normally - there are a lot of STP packets showing up. I did some checking around, it looks like STP is involved in bridging and more complex networking setups (involving switches, for example)... but it shouldn't be found on a home network, especially where there's no bridging whatsoever. These STP packets don't show up on packet captures done from any other computer. I've attached a packet capture from the affected computer here, since the forums won't let me attach a .pcapng file.

Here's the output from a few commands I ran during past troubleshooting sessions:

Code: Select allsudo ifconfig
eth0      Link encap:Ethernet  HWaddr e0:db:55:b5:fe:06 
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:12455 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7781 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000

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