The server configuration has the ability to "push" certain network configuration options to the clients. These include IP addresses, routing commands, and a few connection options. OpenVPN offers two types of interfaces for networking via the Universal TUN/TAP driver. It can create either a layer-3 based IP tunnel (TUN), or a layer-2 based Ethernet TAP that can carry any type of Ethernet traffic. OpenVPN can optionally use the LZO compression library to compress the data stream. Port 1194 is the official IANA assigned port number for OpenVPN. Newer versions of the program now default to that port. A feature in the 2.0 version allows for one process to manage several simultaneous tunnels, as opposed to the original "one tunnel per process" restriction on the 1.x series. OpenVPN's use of common network protocols (TCP and UDP) makes it a desirable alternative to IPsec in situations where an ISP may block specific VPN protocols in order to force users to subscribe to a higher-priced, "business grade" service tier. For example, Comcast previously declared that their @Home product was, and had always been, designated as a residential service and did not allow the use of commercial applications. Their argument was that conducting remote work via a VPN can adversely affect the network performance of their regular residential subscribers. They offered an alternative, @Home Professional, this would cost more than @Home product. So, anyone wishing to use VPN would have to subscribe to higher-priced, business-grade service tier. When OpenVPN uses Transmission Control Protocol (TCP) transports to establish a tunnel, performance will be acceptable only as long as there is sufficient excess bandwidth on the un-tunneled network link to guarantee that the tunneled TCP timers do not expire. If this becomes untrue, performance falls off dramatically. This is known as the "TCP meltdown problem". Security OpenVPN offers various internal security features. It has up to 256-bit encryption through the OpenSSL library, although some service providers may offer lower rates, effectively providing some of the fastest VPN available to consumers. It runs in userspace instead of requiring IP stack (therefore kernel) operation. OpenVPN has the ability to drop root privileges, use mlockall to prevent swapping sensitive data to disk, enter a chroot jail after initialization, and apply a SELinux context after initialization. OpenVPN runs a custom security protocol based on SSL and TLS, rather than supporting IKE, IPsec, L2TP or PPTP. OpenVPN offers support of smart