Basic Principles of TCP/IP Configuration for R/3 Servers 

Basic Principles

To transmit data between two hosts in one network, you need two network adapters (network interface card, NIC). One adapter sends a data packet and the other one receives it.

An IP address (IP = Internet protocol) is assigned to each network adapter. These numerical IP addresses are represented in the form nnn.nnn.nnn.nnn, where nnn is a number from 0 to 255 (for example, 192.168.1.10). An IP address functions as a unique ID for identifying the sender and the receiver in a network with multiple hosts.

The IP name is the name under which the network adapter is known in the network. An IP name is assigned to each IP address. This simplifies the use of IP addresses. This IP name is often mistakenly described as the host name.

The host name or computer name is a logical name for the host itself and is set in the operating system. The operating system knows its own host under its host name. You can query this name under UNIX or Windows NT by using the command hostname .

The IP name is mapped to the IP addresses using a name database. Here, it can be a local host file, or a name resolution service, such as DNS (Domain Name System/Service) or WINS (Windows Internet Naming Service).

If the relevant host only has one network adapter, the host name and the IP name are normally identical. In this case, there is a unique relationship between the logical host name and the IP name (or IP address). This means that this host can be addressed by other computers using its host name.

Terminology

SAP server

All hosts (computers) that belong to an SAP System (database server and application server)

Database server

Host on which the database service runs. If an R/3 instance (central instance or dialog instance) also runs on the database server, the server must be handled like an application server when you configure it.

Application server

Host on which an R/3 application service runs (central instance or dialog instance)

Server network

High speed network segment through which the SAP servers communicate with each other

Access network (frontend network)

All network segments through which the frontend is connected with the application servers

IP address

Network address in the Internet protocol (for example, 192.5.2.1), assigned to a network adapter

IP name

Logical name for an IP address. Is often equated with the host name, although the relationship of the host name and the IP name is not always unique.

Host name

Logical name of the host. It is normally assigned like the IP name of an IP address for the host. A host can have several IP addresses and IP names, but it can only have one host name.

Multihomed Hosts

If a host has multiple network adapters (multiple NICs) or multiple IP addresses for each network adapter, it is called a multihomed host. In this case, the relationship between the IP addresses (with the assigned IP names) and the host name is no longer unique. The host name can be identical to the IP name for an IP address, or it can take on its own unique name. If a multihomed host is addressed by another host, one of the IP names (or the corresponding IP address) must be used. In the following graphic, LAN1 must use the IP name ABC to address the host ABC, whereas LAN2 must use the IP name XYZ to address the same host.

The name you choose by which a host is addressed, influences the route of the data traffic in the network. Application programs do not usually know the various IP names, or their accompanying LAN segments, but they do know the logical host name. Therefore, choosing the right host name is very important. If static IP routes are used, you can also access IP names and/or IP addresses that are not in your own subnet.

Using IP Routing to Choose the Route

If you want o use TCP/IP to send a data packet, the network layer (layer 3 in the OSI layer model or the IP layer) must determine if and how the target IP address can be accessed. The routing information necessary for this is stored in the routing table. You can set the entries in the routing table as being static (manually) or dynamic (using the routing daemon process). The entire route to the target address is not described in the routing table, instead, only the route up to the next node (next hop) to which the data packet is forwarded. There, a check is made in one of its own routing tables as to how the target address should be accessed. This is called an indirect route, since the route goes through at least one gateway. If the address can be directly accessed, this is called a direct route.

There are three ways of defining the target address as the routing entry:

Example of a Simple Route

In this example, the three hosts are connected together by network A and network B:

A host is usually addressed by its host name. If Host 3 makes a connection to Host 1, the target address 192.5.5.7 (R1) is addressed. This connection normally goes over network A. If you want the connection to the same target address to run over network B instead, you must have a corresponding routing entry in Host 3. You may want to route the connection over network B, for example, to increase performance (network B is faster than network A). For communication to run in both directions over network B, there must also be a corresponding routing entry for Host 3 on Host 1.

Example of Routing under UNIX

The above example described an indirect host route. The target address is a complete IP address (a host route), and it is also accessed through a gateway using the IP name R1B (an indirect route). On UNIX hosts, you can display the routing table by using the command netstat –r . For indirect routes, the flag G is used, and for host routes, the flag H is used. To create an indirect route, you must specify in the command route add a Metric (hop count) greater than 0.

Action

Command

Create route on host 1:

route add R3 R3B 1

Create route on host 3:

route add R1 R1B 1

Display all static routes:

netstat –r

Test routes:

traceroute

 

 

Host 3:

      

Host 1:

    

Destination

Gateway

Flag

  

Destination

Gateway

Flag

R1

R1B

UGH

  

R3

R3B

UGH

 

Example of Routing Under Windows NT

On Windows NT hosts, you can display the routing table by using the command route print . Indirect routes are indicated by a Metric = 1 and are made defaults with the command route add .

Action

Command

Create route on host 1:

route add R3 R3B 1

Create route on host 3:

route add R1 R1B 1

Display all static routes:

route print

Test routes:

tracert

 

 

Host 3:

      

Host 1:

    

Network address

Gateway address

Metric

  

Network address

Gateway address

Metric

R1

R1B

1

  

R3

R3B

1