Cabletron Systems EMM-E6 Ethernet Manual De Usuario
CHAPTER 1:
INTRODUCTION
1-26
EMM-E6 User’s Guide
Subnet addresses, when used with routing, allow discrimination between
devices and groups of devices based on IP addresses. Networks of
different subnets, even those on the same physical network segment, may
be isolated, from a functional standpoint, from one another through the
implementation of routing. Repeaters, bridges, and switches, which
operate at the Data Link layer of the OSI model, make their decisions
based on MAC addresses. Network devices such as routers, servers, and
client stations can use IP addressing to recognize transmissions intended
for them. If a station on one routed subnet sees a transmission from
another subnet, it will ignore the packet without concern over who it is
intended for. To overcome this subnetwork blindness a router is used. Any
station or device which implements subnet masking needs to be
configured with an address for that subnet’s Default Gateway. When the
station or device transmits packets intended for a different subnetwork
than the one it identifies itself as belonging to, the transmission is also
sent to the Default Gateway, where the gateway or router will make the
determination of where the packet is sent.
devices and groups of devices based on IP addresses. Networks of
different subnets, even those on the same physical network segment, may
be isolated, from a functional standpoint, from one another through the
implementation of routing. Repeaters, bridges, and switches, which
operate at the Data Link layer of the OSI model, make their decisions
based on MAC addresses. Network devices such as routers, servers, and
client stations can use IP addressing to recognize transmissions intended
for them. If a station on one routed subnet sees a transmission from
another subnet, it will ignore the packet without concern over who it is
intended for. To overcome this subnetwork blindness a router is used. Any
station or device which implements subnet masking needs to be
configured with an address for that subnet’s Default Gateway. When the
station or device transmits packets intended for a different subnetwork
than the one it identifies itself as belonging to, the transmission is also
sent to the Default Gateway, where the gateway or router will make the
determination of where the packet is sent.
The use of subnet addresses on the network means using a Subnet Mask
in conjunction with each IP address.
in conjunction with each IP address.
1.10.5
Subnet Masks
The purpose of the Subnet Mask is to indicate the part of the Host ID that
is being used as a subnet address. By default no part of the Host ID is
used, and therefore, the default or “Natural Mask” masks just the octets
that comprise the Network ID. Table 1-5 shows the default masks for the
four classes of IP networks.
is being used as a subnet address. By default no part of the Host ID is
used, and therefore, the default or “Natural Mask” masks just the octets
that comprise the Network ID. Table 1-5 shows the default masks for the
four classes of IP networks.
Table 1-5. Class and Default Masks
Network Class
Length of Network ID
Default Mask
Class A
X.
255. 0. 0. 0
Class B
X. X.
255. 255. 0. 0
Class C
X. X. X.
255. 255. 255. 0
CH1Book Page 26 Wednesday, March 20, 1996 7:48 AM