to send multicast packets during an election process. One exception to this rule is when a physical router is configured with a higher priority than the current primary/active, which means that on connection to the network it will pre-empt the primary/active status. This allows a system administrator to force a physical router to the primary/active state immediately after booting, for example when that particular router is more powerful than others within the virtual router. The secondary/standby router with the highest priority becomes the primary/active router by raising its priority above that of the current primary/active. It will then take responsibility for routing packets sent to the virtual gateway's MAC address. In cases where secondary/standby routers all have the same priority, the secondary/standby router with the highest IP address becomes the primary/active router. All physical routers acting as a virtual router must be in the same local area network (LAN) segment. Communication within the virtual router takes place periodically. This period can be adjusted by changing advertisement interval timers. The shorter the advertisement interval, the shorter the black hole period, though at the expense of more traffic in the network. Security is achieved by responding only to first hop packets, though other mechanisms are provided to reinforce this, particularly against local attacks. The election process is made orderly through the use of skew time, derived from a router's priority, and used to reduce the chance of the thundering herd problem occurring during the election. The skew time is given by the formula (256 − Priority)/256 (expressed in milliseconds). Secondary/standby router utilization can be improved by load sharing. History VRRP is described in Internet Engineering Task Force (IETF) publication RFC 5798, which is an open standard, but Cisco claims that Hot Standby Router Protocol, a similar protocol with essentially the same facility, is patented and licensed; however, in 2001, in reply to a direct request, Robert Barr of Cisco replied that they will not assert any patent claims unless someone tried to assert a claim against Cisco. IBM also claims covering patents and their statement is readable on the IETF webpage. All patents in question have expired. Derivatives Mellanox offers MAGP, a proprietary protocol based on VRRP that allows active-active operation. Foundry Networks developed VRRP-E(Extended), a proprietary version of VRRP that avoids a few limitations of RFC 3768 See also Common Address Redundancy Protocol (CARP) – a non-proprietary, patent-free, and unrestricted alternative