RMS compact
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Appendix C
This appendix has two sections:
Reference
and
Troubleshooting
.
Reference
This section discusses Communities, IP Addresses, Sub net masking, and routers/gateways.
Communities
A community is a string of printable ASCII characters that identifies a user group with the same access
privileges. For example, a common community name is “public.”
For security purposes, the SNMP agent validates requests before responding. The agent can be configured so
that only managers that are members of a community can send requests and receive responses from a
particular community. This prevents unauthorized managers from viewing or changing the configuration of a
device.
IP Addresses
Every device on an internetwork must be assigned a unique IP (Internet Protocol) address. An IP address is a
32-bit value comprised of a network ID and a host ID. The network ID identifies the logical network to which a
particular device belongs. The host ID identifies the particular device within the logical network. IP addresses
distinguish devices on an internetwork from one another so that IP packets are properly transmitted.
IP addresses appear in dotted decimal (rather than in binary) notation. Dotted decimal notation divides the 32-
bit value into four 8-bit groups, or octets, and separates each octet with a period. For example, 199.217.132.1 is
an IP address in dotted decimal notation.
To accommodate networks of different sizes, the IP address has three divisions - Classes A for large, B for
medium, and C for small. The difference among the network classes is the number of octets reserved for the
network ID and the number of octets reserved for the host ID.
Class
Value of First
Octet
Network ID
Host ID
Number of
Hosts
A
1-126
first octet
last three octets
16,387,064
B
128-191
first two octets
last two octets
64,516
C 192-223
first
three
octets
last octet
254
Any value between 0 and 255 is valid as a host ID octet except for those values the InterNIC reserves for other
purposes.
Value
Purpose
0, 255
Subnet masking
127
Loopback testing and interprocess communication on
local devices
224-254
IGMP multicast and other special protocols
Subnetting and Subnet Masks
Subnetting divides a network address into subnetwork addresses to accommodate more than one physical
network on a logical network.
For example: A Class B company has 100 LANs (Local Area Networks) with 100 to 200 nodes on each LAN.
To classify the nodes by its LANs on one main network, this company segments the network address into 100
subnetwork addresses. (If the Class B network address is 150.1.x.x, the address can be segmented further from
150.1.1.x through 150.1.100.x.)
A subnet mask is a 32-bit value that distinguishes the network ID from the host ID for different subnetworks on
the same logical network. Like IP addresses, subnet masks consist of four octets in dotted decimal notation.
You can use subnet masks to route and filter the transmission of IP packets among your subnetworks. The