Method for operating a communication system having redundant routers, in which - datagrams are forwarded within the communication system from source communication devices to destination communication devices by routers on the basis of routing information stored in routing tables of the routers, - a virtual router that has an assigned group (11, 12) of multiple routers and an allocated virtual data link layer address is configured as the default gateway for respective communication terminals, - routers from the same group assigned to a virtual router select one router (104, 103) from among one another that is operated as the active default gateway, the routers that are not operated as the active default gateway being configured and operated as reserve gateways, - the reserve gateways adopt respective address allocations transmitted by the respective active default gateway in their configuration directly and without results of a training procedure of their own for address allocations, - the reserve gateways select a new active default gateway from among one another if a previously active default gateway fails, - the new active default gateway adopts the address allocations transmitted before the failure and the virtual data link layer address allocated to the virtual router for its operation as the active default gateway, characterized in that - the reserve gateways request from the respective active default gateway a transmission of stored address allocations between data link layer addresses and network layer addresses of detected communication devices, - the respective active default gateway (104, 103) transmits all of the respective stored address allocations in bundled form to a requesting reserve gateway only in response to a request for stored address allocations that is received from a reserve gateway, - a quality of a synchronization by the reserve gateways is periodically checked by virtue of the reserve gateways specifying a number of received address allocations in their respective request, with the active default gateway sending all of its address allocations again if it discovers a discrepancy with respect to the transmitted number. - datagrams are forwarded within the communication system from source communication devices to destination communication devices by routers on the basis of routing information stored in routing tables of the routers, - a virtual router that has an assigned group (11, 12) of multiple routers and an allocated virtual data link layer address is configured as the default gateway for respective communication terminals, - routers from the same group assigned to a virtual router select one router (104, 103) from among one another that is operated as the active default gateway, the routers that are not operated as the active default gateway being configured and operated as reserve gateways, - the reserve gateways adopt respective address allocations transmitted by the respective active default gateway in their configuration directly and without results of a training procedure of their own for address allocations, - the reserve gateways select a new active default gateway from among one another if a previously active default gateway fails, - the new active default gateway adopts the address allocations transmitted before the failure and the virtual data link layer address allocated to the virtual router for its operation as the active default gateway, - the reserve gateways request from the respective active default gateway a transmission of stored address allocations between data link layer addresses and network layer addresses of detected communication devices, - the respective active default gateway (104, 103) transmits all of the respective stored address allocations in bundled form to a requesting reserve gateway only in response to a request for stored address allocations that is received from a reserve gateway, - a quality of a synchronization by the reserve gateways is periodically checked by virtue of the reserve gateways specifying a number of received address allocations in their respective request, with the active default gateway sending all of its address allocations again if it discovers a discrepancy with respect to the transmitted number.