High availability BGP4 is based on redundant hardware as well as redundant
software that replicates the RUN state of BGP4. There are two copies,
respectively active and backup, of BGP4 running on two separate redundant
hardware platforms. All BGP4 internal implementations apply various
methods to replicate the running state of BGP4 independently of peer
network routers. When this hardware or software fails on one redundant
hardware platform, peer routers are unaware of the failure. Internally,
based on duplicative states, the local router recovers from the failure
and keeps the protocol running. During the recovery period, the local
router can bring up a backup again. In the HA architecture, these
activities are not detected by peer routers, such that there is no
instability to the Internet backbone caused by BGP4 failure.