Host Attach. In ExtremeXOS software, HA is part of ESRP that allows you to connect active hosts directly to an ESRP switch; it allows configured ports to continue Layer 2 forwarding regardless of their ESRP status.


This is the communication mode in which a device can either send or receive data, but not simultaneously. (Devices at 1 Gbps or higher do not run in half-duplex mode; they run only in full-duplex mode.)

heartbeat message

A UDP data packet used to monitor a data connection, polling to see if the connection is still alive.
 In general terms, a heartbeat is a signal emitted at regular intervals by software to demonstrate that it is still alive. In networking, a heartbeat is the signal emitted by a Level 2 Ethernet transceiver at the end of every packet to show that the collision-detection circuit is still connected.

hitless failover

In the Extreme Networks implementation on modular switches and SummitStacks, hitless failover means that designated configurations survive a change of primacy between the two MSMs (modular switchtes) or master/backup nodes (SummitStacks) with all details intact. Thus, those features run seamlessly during and after control of the system changes from one MSM or node to another.


  1. A computer (usually containing data) that is accessed by a user working on a remote terminal, connected by modems and telephone lines.
  2. A computer that is connected to a TCP/IP network, including the Internet. Each host has a unique IP address.


Hypertext Transfer Protocol is the set of rules for transferring files (text, graphic images, sound, video, and other multimedia files) on the World Wide Web. A Web browser makes use of HTTP. HTTP is an application protocol that runs on top of the TCP/IP suite of protocols. (RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1)


Hypertext Transfer Protocol over Secure Socket Layer, or HTTP over SSL, is a web protocol that encrypts and decrypts user page requests as well as the pages that are returned by the Web server. HTTPS uses Secure Socket Layer (SSL) as a sublayer under its regular HTTP application layering. (HTTPS uses port 443 instead of HTTP port 80 in its interactions with the lower layer, TCP/IP.) SSL uses a 40-bit key size for the RC4 stream encryption algorithm, which is considered an adequate degree of encryption for commercial exchange.