Under some circumstances, there may be connectivity between two SNMPv2 entities, but the NBP mapping machinery may be broken, e.g.,
An SNMPv2 entity acting in a manager role which is dedicated to AppleTalk management might choose to alleviate some of these failures by directly implementing the router portion of NBP. For example, such an entity might already know all the zones on the AppleTalk internet and the networks on which each zone appears. Given an NBP lookup which fails, the entity could send an NBP FwdReq to the network in which the agent was last located. If that failed, the station could then send an NBP LkUp (NBP lookup packet) as a directed (DDP) multicast to each network number on that network. Of the above (single) failures, this combined approach will solve the case where either the local router's BrRq-to-FwdReq mechanism is broken or the remote router's FwdReq-to-LkUp mechanism is broken.