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 .