Specifications

Appendix C Operating Environment Installation and Operation Manual
C-10 IP Environment FCD-E1LC Ver. 1.0
In most applications, the binary subnet mask is built as a contiguous string of
“
ones ”, followed by a number of “ zeros ” (the number of “ zeros ” is selected as
needed, to complete the number of subnet mask bits to 32). Therefore, when
this conventional approach is used, the subnet mask can also be specified simply
by stating the number of “
ones ” in the mask. For example, the subnet mask
shown above is specified by stating that it comprises 28 bits.
IP Routing Principles
The exchange of information between IP hosts is made in packets using the
structure specified by the IP protocol. As explained in the
IP Packet Structure
section above, IP frames carry, within their header, the IP addresses of the
destination and source hosts.
In accordance with the IP protocol, an IP host checks the addresses of all the
received frames, and accepts only frames carrying its own IP address as the
destination.
The source address is then used to enable the destination to respond to the
source.
An IP host will also respond to broadcasts (frames whose destination host
identifier is “
all-ones” ).
IP hosts support additional protocols within the IP suite, e.g., protocols used for
connectivity checking, maintenance, etc. Therefore, IP hosts will accept additional
types of messages, which are beyond the scope of this description.
When checking the destination address of an IP frame, an IP host starts by
checking the network identifier. If the network identifier is different, the host will
immediately reject the frame. Therefore, IP hosts can communicate only if they
have the same network identifier.
For example, this means that when a management station managing the
FCD-E1LC is connected directly, through a LAN, to the FCD-E1LC Ethernet
management port, the network identifier part of the IP address assigned to the
FCD-E1LC Ethernet port must be identical to the network identifier of the
management station.
To enable hosts located on different IP networks to communicate, IP routers are
needed. Each router monitors the flowing IP traffic and identifies the IP
addresses of the local hosts connected to them, and then communicates this
information to all the other routers, using a special protocol (the Routing Internet
Protocol, RIP). Therefore, a router can determine to which other router to send a
packet with a foreign IP address.
RAD agents, for example, the management agent of the FCD-E1LC, also use a
RAD proprietary routing protocol, similar to RIP, for handling RAD management
traffic.
The user can increase the routing efficiency by specifying a default gateway to
handle IP traffic to other networks (this is always an IP router). When a default
gateway address is specified, packets with IP destinations located on other
Note
Note