The access network is the network between the application hosts and the front ends, also known as the company network. In the access network, it is important that the connection between the SAP front ends and the application host on which the dialog service resides is reliable. Distinguish this from the server network, which links the application hosts to one another and to the database host.
The topology of the access network normally has some degree of built-in redundancy. If connection to a particular application host fails, clients connected to the failed host can reconnect to other hosts, which then take over the dialog service workload.
The exception to this rule is the message server, which requires a higher level of availability, such as a second network interface card (NIC) and switchover software. For more information, see the recommendations in Server Network. If the message host is not accessible, clients using standard access with logon load balancing cannot connect to the SAP system.
Therefore, we recommend installing a backbone and making this highly available. Use standard network components for this. Reserve the backbone exclusively for communication between the connected switches and routers.