Just tested a few TP-Link USB WiFi dongles: summary TL-WN722N and TL-WN823N 
work, TL-WN821N has problems; it comes up without errors, but when being 
listed, reports being down even though it is up and working; see below. 
This is just for info; note the driver is rtl8192cu which I suspect is the 
problem. (BBB ver c, kernel: 4.1.13-ti-r36, Debian Jessie, release 8.2). If 
you are close to router, then the TL-WN823N is small and seems to work 
well. No need to read the rest of this post unless you are interested in 
details.+

> sudo ip ro flush dev wlan0
> sudo ip a flush dev wlan0
> sudo ip link set dev wlan0 down
> sudo ip link set dev wlan0 up
> sudo ip addr add 192.168.0.174/24 dev wlan0
> ip link show dev wlan0
3: wlan0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN 
mode DORMANT group default qlen 1000
    link/ether 10:fe:ed:12:2d:8b brd ff:ff:ff:ff:ff:ff
> sudo ip route add 192.168.0.0/24 dev wlan0 metric 303
> ip route show
default via 192.168.0.1 dev eth0 
192.168.0.0/24 dev eth0  proto kernel  scope link  src 192.168.0.244 
192.168.0.0/24 dev wlan0  proto kernel  scope link  src 192.168.0.174 
192.168.0.0/24 dev wlan0  scope link  metric 303 
192.168.0.118 via 127.0.0.1 dev lo  metric 202 
> ping -c 2 192.168.0.1 -I wlan0
PING 192.168.0.1 (192.168.0.1) from 192.168.0.174 wlan0: 56(84) bytes of 
data.
>From 192.168.0.174 icmp_seq=1 Destination Host Unreachable
>From 192.168.0.174 icmp_seq=2 Destination Host Unreachable

--- 192.168.0.1 ping statistics ---
2 packets transmitted, 0 received, +2 errors, 100% packet loss, time 1006ms
pipe 2
> 
> ifconfig
eth0      Link encap:Ethernet  HWaddr d0:5f:b8:fc:51:e2  
          inet addr:192.168.0.244  Bcast:192.168.0.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:3146 errors:0 dropped:189 overruns:0 frame:0
          TX packets:867 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:271925 (265.5 KiB)  TX bytes:102062 (99.6 KiB)
          Interrupt:170 

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:512 errors:0 dropped:0 overruns:0 frame:0
          TX packets:512 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:42032 (41.0 KiB)  TX bytes:42032 (41.0 KiB)

wlan0     Link encap:Ethernet  HWaddr 10:fe:ed:12:2d:8b  
          inet addr:192.168.0.174  Bcast:0.0.0.0  Mask:255.255.255.0
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

> ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group 
default 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state 
UP group default qlen 1000
    link/ether d0:5f:b8:fc:51:e2 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.244/24 brd 192.168.0.255 scope global eth0
       valid_lft forever preferred_lft forever
3: wlan0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN 
group default qlen 1000
    link/ether 10:fe:ed:12:2d:8b brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.174/24 scope global wlan0
       valid_lft forever preferred_lft forever
4: usb0: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN group 
default qlen 1000
    link/ether d0:5f:b8:fc:51:e0 brd ff:ff:ff:ff:ff:ff
    inet 192.168.7.2/30 brd 192.168.7.3 scope global usb0
       valid_lft forever preferred_lft forever
>

HOWEVER, FROM UBUNTU HOST, one can ssh to 192.168.0.174 and also

> ping -c 2 192.168.0.174
PING 192.168.0.174 (192.168.0.174) 56(84) bytes of data.
64 bytes from 192.168.0.174: icmp_seq=1 ttl=64 time=0.447 ms
64 bytes from 192.168.0.174: icmp_seq=2 ttl=64 time=0.412 ms

but could this be going through the eth0 connection on the BBB?

--- 192.168.0.174 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 999ms
rtt min/avg/max/mdev = 0.412/0.429/0.447/0.027 ms
> 

This is probably a Debian problem with the rtl8192cu driver, although it 
works with the TL-WN823N; I thought others might like to know not to use 
the TL-WN821N to save time

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