An oldie, but it may still help

Several Ubuntu releases ago, my network connection became pathetically slow when I was using my DSL connection. I still have no idea what caused it, but the following worked well to restore the connection speed (sadly, these are the only notes I've ever shared prior to this blog):

Add the following to /etc/sysctl.conf, where "[VALUE]" should either be 131072, 262144, or 524288. I had the best luck with 262144, but it might be wise to try them all:

# Tweaks for faster broadband...
net.core.rmem_default = [VALUE]
net.core.rmem_max = [VALUE]
net.core.wmem_default = [VALUE]
net.core.wmem_max = [VALUE]
net.ipv4.tcp_wmem = 4096 87380 [VALUE]
net.ipv4.tcp_rmem = 4096 87380 [VALUE]
net.ipv4.tcp_mem = 262144 262144 [VALUE]
net.ipv4.tcp_rfc1337 = 1
net.ipv4.ip_no_pmtu_disc = 0
net.ipv4.tcp_sack = 1
net.ipv4.tcp_fack = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_ecn = 0
net.ipv4.route.flush = 1

Then enter command 'sysctl -p' to reload sysctl settings