Module Properties Dialog Box - Port Configuration Tab Overview (1756-ENET, -ENBT, -ENBF; 1788-EN2DN)
Use this tab to configure the IP Addresses and BOOTP for the 1756-ENET, 1756-ENBT, 1756-ENBF, and 1788-EN2DN modules. You can:
- Set your IP address
- Set your Subnet Mask
- Set your Gateway Address
- Set your domain name
- Set your Primary and Secondary DNS Server Addresses
- Enable or disable BOOTP to check for DNS addressing
Parameters
Listed below are explanations of each entry field on the Configuration tab for the 1756-ENET module. The default values are indicated in bold.
IP Address
The IP address identifies each node on the IP network (or system of connected networks). Each TCP/IP node on a network (including the Ethernet module) must have a unique IP address.
This value needs to match the IP address entered on the General Tab. If the value is incorrect on the General Tab, the controller will not know how to reach the ENet module if it sits on a Ethernet network., and not in a local chassis.
If you re-configure your Enet module with a different IP Address, when you select the "Set" button you may lose communications with your module until you go back and set the new IP address on the General Tab and re-download to the controller.
The IP address is 32 bits long and has a net ID part and a host ID part. Each network is a Class A, Class B, or Class C network. The class of a network determines how an IP address is formatted.
Each node on the same physical network must have an IP address of the same class and must have the same net ID. Each node on the same network must have a different host ID thus giving it a unique IP address.
IP addresses are written as four decimal integers (0-255) separated by periods where each integer gives the value of one byte of the IP address.
TIP:
The first octet of the IP Address may not be 127, or a number greater than 223. If any of these values are entered and you attempt to download this configuration using the Set button, an error message is displayed, and no values are sent to the module.
For example, the 32-bit IP address:
00000011 00000000 00000000 00000001 is written as 3.0.0.1.
You can distinguish the class of an IP address from the first integer in its dotted-decimal IP address as follows:
Range of
first integer | Class | Range of
first integer | Class |
0 -127 | A | 192 - 223 | C |
128 -191 | B | 224 - 255 | other |
TIP:
Contact your network administrator or the Network Information Center for a unique IP address to assign to your module.
Subnet Mask
Subnet addressing is an extension of the IP address scheme that allows a site to use a single net ID for multiple physical networks. Routing outside of the site continues by dividing the IP address into a net ID and a host ID via the class. Inside a site, the subnet mask is used to redivide the IP address into a custom net ID portion and host ID portion. This field is set to 0.0.0.0 by default.
For example, using Network 2 (a Class B network) in the previous example and add another physical network. Selecting the following subnet mask would add two additional net ID bits allowing for four physical networks:
11111111 11111111 11000000 00000000 = 255.255.192.0
Two bits of the Class B host ID have been used to extend the net ID. Each unique combination of bits in the part of the host ID where subnet mask bits are 1 specifies a different physical network.
The new configuration is:
A second network with Hosts D and E has been added. Gateway G2 connects Network 2.1 with Network 2.2. Hosts D and E will use Gateway G2 to communicate with hosts not on Network 2.2. Hosts B and C will use Gateway G to communicate with hosts not on Network 2.1. When B is communicating with D, G (the configured Gateway for B) will route the data from B to D through G2.
Gateway Address
A gateway connects individual physical networks into a system of networks. When a node needs to communicate with a node on another network, a gateway transfers the data between the two networks. The following figure shows gateway G connecting Network 1 with Network 2.
When host B with IP address 128.2.0.1 communicates with host C, it knows from C's IP address that C is on the same network. In an Ethernet environment, B can then resolve C's IP address to a MAC address (via ARP) and communicate with C directly.
When host B communicates with host A, it knows from A's IP address that A is on another network (the net IDs are different). In order to send data to A, B must have the IP address of the gateway connecting the two networks. In this example, the gateway's IP address on Network 2 is 128.2.0.3.
The gateway has two IP addresses (128.1.0.2 and 128.2.0.3). The first must be used by hosts on Network 1 and the second must be used by hosts on Network 2. To be usable, a host's gateway must be addressed using a net ID matching its own.
This field is set to 0.0.0.0 by default.
Domain Name
Enter the DNS entry for the module, if desired. This field can be left blank.
Primary/Secondary DNS Server Address
This Configuration option allows a server to accept a "text-based" address and perform a database lookup to convert that address to an IP address that can be used by the network. If a message uses a host name address, it must be converted somehow to an IP address before it can be sent to the destination controller. When the Ethernet module of the sending controller has a DNS server address configured, then the DNS server is used to take the host name address and convert it to the IP address of the destination Ethernet module and the message can be sent. The two fields are set to 0.0.0.0 by default.
Enable Bootp
BOOTP (Bootstrap protocol) is a low-level protocol that provides configurations to other nodes on a TCP/IP network with DOS, Microsoft Windows, Windows NT, Windows 95, VMS and HP- UNIX platforms. BOOTP configuration files let you automatically assign IP addresses to the Ethernet module. You can also obtain subnet masks and gateway addresses from BOOTP. BOOTP is enabled as the default.
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