diff --git a/README.md b/README.md index 905ec8ba6..c7979b937 100644 --- a/README.md +++ b/README.md @@ -104,7 +104,7 @@ On CentOS check `/etc/sysconfig/iptables` for IPTables rules. For other distribu ZeroTier One peers will automatically locate each other and communicate directly over a local wired LAN *if UDP port 9993 inbound is open*. If that port is filtered, they won't be able to see each others' LAN announcement packets. If you're experiencing poor performance between devices on the same physical network, check their firewall settings. Without LAN auto-location peers must attempt "loopback" NAT traversal, which sometimes fails and in any case requires that every packet traverse your external router twice. -Users behind certain types of firewalls and "symmetric" NAT devices may not able able to connect to external peers directly at all. ZeroTier has limited support for port prediction and will *attempt* to traverse symmetric NATs, but this doesn't always work. If P2P connectivity fails you'll be bouncing UDP packets off our relay servers resulting in slower performance. Some NAT router(s) have a configurable NAT mode, and setting this to "full cone" will eliminate this problem. If you do this you may also see a magical improvement for things like VoIP phones, Skype, BitTorrent, WebRTC, certain games, etc., since all of these use NAT traversal techniques similar to ours. +Users behind certain types of firewalls and "symmetric" NAT devices may not able to connect to external peers directly at all. ZeroTier has limited support for port prediction and will *attempt* to traverse symmetric NATs, but this doesn't always work. If P2P connectivity fails you'll be bouncing UDP packets off our relay servers resulting in slower performance. Some NAT router(s) have a configurable NAT mode, and setting this to "full cone" will eliminate this problem. If you do this you may also see a magical improvement for things like VoIP phones, Skype, BitTorrent, WebRTC, certain games, etc., since all of these use NAT traversal techniques similar to ours. If a firewall between you and the Internet blocks ZeroTier's UDP traffic, you will fall back to last-resort TCP tunneling to rootservers over port 443 (https impersonation). This will work almost anywhere but is *very slow* compared to UDP or direct peer to peer connectivity.