Some
users of the BitTorrent client report experiencing slow downloads when
sharing P2P files. This is most likely to occur on computers behind a home
router or software
firewall.
Being behind firewalls, the BitTorrent client may block incoming Bit Torrent
network connections. Given the load balancing and "swarming" nature of the
BitTorrent network, clients unable to take incoming requests for uploads will
naturally be allowed less
bandwidth for downloads.
To solve this problem, consider the following:
When a user starts a BitTorrent client, the client sets up a network
resource called a "port" to allow other Bit Torrent clients to connect onto
it.
Each
port possesses a unique number called the "TCP port number."
A
BitTorrent client normally associates the TCP port number 6881. However, if
this port is busy for some reason, the client will instead try successively
higher ports (6882, 6883, and so on up to a limit of 6999). In order for
outside BitTorrent clients to reach this one, they must be able to connect
to the correct port.
When connecting to another BitTorrent client, the requesting client will
first try port 6881, then 6882, and so on. However, if the computer is on a
firewalled network, the incoming request may not reach these ports. On the
other hand, if these requests succeed, the accepting client will be able to
download faster.
Firewalls can block nearly all of the ports used by P2P clients. To ensure
the BitTorrent ports are made available to requesting clients, a home router
or firewall can be manually configured to accept them. Most home routers
possess a feature called "Port Range Forwarding" to do this. This feature
allows the administer to tell the firewall where traffic for a given port
number should be directed.
For BitTorrent, many home users set up port forwarding on the TCP range
6881-6889. These ports must be directed to the computer running the
BitTorrent client. If more than one computer on the network may run
BitTorrent, a different range such as 6890-6899 or 6990-6999 can be used for
each. Remember that BitTorrent uses ports in the 6881-6999 only.
Many people don't realize that Windows XP computers include the built in
Windows Firewall. If port forwarding is
set up on a home router, but Windows Firewall is running on the BitTorrent
client computer, incoming requests may still fail to reach the client.
Ensure the Windows Firewall is either disabled or is set up to allow the
appropriate BitTorrent ports to pass through. The same recommendation
applies to other software firewalls.
On
home networks without a router, the software firewall (Windows Firewall,
ZoneAlarm, or other) must be set up to provide the equivalent forwarding or
pass-through capability as needed.
