Distech Controls ECLYPSE APEX, Руководство пользователя

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18 ECLYPSE APEX
About Routers, Switches, and Hubs
The differences between a hub, switch, and router are discussed in the table below.
Device Type Description
Hub
Every incoming data packet is repeated on every other port on the device. Due to this, all traffic is
made available on all ports which increase data packet collisions that affect the entire network, thus
limiting its data carrying capacity.
Switch
A switch creates a one-to-one virtual circuit that directs IP packets directly to the port that the
destination computer is connected to.
Router
Like a switch, a router learns the IP addresses of all devices connected to any of its RJ-45 ports to
create a routing table. If a data packet arrives at the router’s port with a destination IP address that is:
– Found in the router’s routing table, the router forwards the data packet to the appropriate port
for the device that has this IP address.
– For a network with a different network ID than the current network ID, the router forwards the
data packet to the uplink port where the next router will again either recognize the network ID
and route the data packet locally or again forwards the data packet to the uplink port. By be-
ing exposed to traffic, a router adds to its routing table the pathways necessary to resolve a
data packet's pathway to its final destination, by passing through one or more routers if nec-
essary.
Connecting a Router
The way a router is connected to other devices changes its function.
1
UPLINK
2 3 4
1
UPLINK
2 3 4
ROUTER
A
ROUTER
B
Connection to use ROUTER A as a router
To
Device
To
Device
To
Device
To
Device
To
Device
To
Device
To
Device
To
WAN
1
UPLINK
2 3 4
1
UPLINK
2 3 4
ROUTER
A
ROUTER
B
Connection to NOT use ROUTER A as a router
To
Device
To
Device
To
Device
To
Device
To
Device
To
Device
To
WAN
UPLINK
Function is
Not Used
Figure 2: The Way a Router is Connected Changes its Function
On some routers, the uplink port is marked as WAN (Wide Area Network) and the numbered ports are
to be connected to the LAN (Local Area Network) devices.
Network Address Translation / Firewall
A router’s uplink port provides Network Address Translation (NAT) and firewall functions.
NAT is a method to hide the private IP addresses of a range of devices (connected to LAN ports) be-
hind a single IP address presented at the WAN uplink port. NAT uses a mechanism to track requests
to WAN IP addresses and readdresses the outgoing IP packets on exit, so they appear to originate
from the router itself. In the reverse communications path, NAT again readdresses the IP packet’s
destination address back to the original source private IP address.
Due to this tracking mechanism, only requests originating from the LAN side can initiate communica-
tions. A request from the WAN to the router cannot be mapped into a private address as there is no
outbound mapping for the router to use to properly readdress it to a private IP address. This is why a
NAT acts as a firewall that blocks unsolicited access to the router’s LAN side.
Most routers allow you to open a port in the firewall so that WAN traffic received at a specific port num-
ber is always forwarded to a specific LAN IP address. The standard port numbers used by ECLYPSE
controllers is explained in chapter
IP Network Protocols and Port Numbers .
IPv4 Communication Fundamentals