Something's wrong with Ubuntu. Since I've upgraded to 13.10, I can't access some websites for no apparent reason. 
I've tried everything imaginable to solve this problem :
Made sure that MTUs are the same,
Disabled IPv6 in both the network manager and used browsers, 
Deactivated my network keys, 
DMZed my computer, 
Used other DNS like Google and OpenDNS, 
Checked that no firewall was running my computer ... 
And it's the same result. I even tried to reinstall Ubuntu a couple of times, but no luck. 
The most annoying thing about it is I can't access wordpress.org! So, there's no way it could be an ISP restriction of some kind. 
When I use a VPN, I can access pretty much anything. 
I'm really frustrated because I have to use wordpress.org very often. 
Any clue? 
ifconfig 
adame@adame-ws:~$ ifconfig
eth0      Link encap:Ethernet  HWaddr 00:26:18:3d:b0:7c  
      inet addr:10.42.0.1  Bcast:10.42.0.255  Mask:255.255.255.0
      inet6 addr: fe80::226:18ff:fe3d:b07c/64 Scope:Link
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:8024 errors:0 dropped:0 overruns:0 frame:0
      TX packets:7966 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000 
      RX bytes:684480 (684.4 KB)  TX bytes:616608 (616.6 KB)
lo        Link encap:Local Loopback  
      inet addr:127.0.0.1  Mask:255.0.0.0
      inet6 addr: ::1/128 Scope:Host
      UP LOOPBACK RUNNING  MTU:65536  Metric:1
      RX packets:8222 errors:0 dropped:0 overruns:0 frame:0
      TX packets:8222 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:0 
      RX bytes:568269 (568.2 KB)  TX bytes:568269 (568.2 KB)
wlan0     Link encap:Ethernet  HWaddr 00:19:70:40:85:eb  
      inet addr:192.168.2.3  Bcast:192.168.2.255  Mask:255.255.255.0
      inet6 addr: fe80::219:70ff:fe40:85eb/64 Scope:Link
      UP BROADCAST RUNNING MULTICAST  MTU:1464  Metric:1
      RX packets:123705 errors:0 dropped:0 overruns:0 frame:0
      TX packets:98141 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000 
      RX bytes:94963545 (94.9 MB)  TX bytes:10387470 (10.3 MB)
/etc/hosts
127.0.0.1   localhost
127.0.1.1   adame-ws
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
tracepath wordpress.org
1:  adame-ws.local                                        0.092ms pmtu 1500
1:  192.168.2.1                                           1.300ms asymm  2 
1:  192.168.2.1                                           1.060ms asymm  2 
2:  no reply
3:  no reply
4:  no reply
5:  no reply
6:  no reply
7:  no reply
8:  no reply
... keep on going like that
ping wordpress.org
adame@adame-ws:~$ ping wordpress.org
PING wordpress.org (66.155.40.250) 56(84) bytes of data.
--- wordpress.org ping statistics ---
10 packets transmitted, 0 received, 100% packet loss, time 9071ms