Method for determining a termination point of at least one tunnel or tunnel segment in a packet switching network, the network comprising a set of routers (A, B, C, D, E, F, G) and links between them, each link having an associated cost, the set of routers and the links forming a network topology referred to as "previous topology", a transit router (RTR) included in the set receiving packets destined for an exit router (RSO) included in the set, an event (E2) modifying the previous topology to a network topology referred to as "subsequent topology", a backup path between the transit router and the exit router being calculated (E3) for the packets on the basis of the subsequent topology, the method comprising the following step (E1), prior to the event: • for each of the routers in the set, calculation of a tree referred to as "initial tree" (SPT(A), SPT(B), SPT(C), SPT(D), SPT(E), SPT(F), SPT(G)), on the basis of the previous topology, said initial tree having as root said each of the routers and having as branches paths of minimum cost between the root and the other routers in the set, the method being characterized in that it additionally comprises at least one cycle of the following steps, after the event: • selection (E4, E7) of a router on the backup path, referred to as "start router" (RDE(c=1), RDE(c=2)), • from the start router, to the exit router along the backup path, identification (E5) of a router, referred to as "last common router" (DRCO(c=1), DRCO(c=2)), for which all the links and routers including itself, between the start router and itself, are common to the backup path and to the initial tree associated with the start router, and, if this last common router is different from the start router, • determination (E6) of the termination point of the tunnel or tunnel segment as being the identified last common router, the tunnel or tunnel segment being intended to save the packets that are transiting between the start router and the identified last common router from entering a microloop caused by the event, the start router selected during the first cycle being the transit router or the router adjacent to the transit router on the backup path. • for each of the routers in the set, calculation of a tree referred to as "initial tree" (SPT(A), SPT(B), SPT(C), SPT(D), SPT(E), SPT(F), SPT(G)), on the basis of the previous topology, said initial tree having as root said each of the routers and having as branches paths of minimum cost between the root and the other routers in the set, • selection (E4, E7) of a router on the backup path, referred to as "start router" (RDE(c=1), RDE(c=2)), • from the start router, to the exit router along the backup path, identification (E5) of a router, referred to as "last common router" (DRCO(c=1), DRCO(c=2)), for which all the links and routers including itself, between the start router and itself, are common to the backup path and to the initial tree associated with the start router, and, if this last common router is different from the start router, • determination (E6) of the termination point of the tunnel or tunnel segment as being the identified last common router, the tunnel or tunnel segment being intended to save the packets that are transiting between the start router and the identified last common router from entering a microloop caused by the event, <EOS>