Contemporary-control-systems EIPR Wired/Wireless VPN Router Application Guide Uživatelský manuál stáhnout pdf (Strana 8)

AG-EIPR0000-BC1 Page 8

Application Guide — EIPR Series

When attaching BACnet devices to IP networks it is

possible that the IP network has been sub-netted

through the use of IP routers. Most IP routers will not

pass broadcast messages which are crucial to

BACnet’s operation. The solution is to incorporate

BACnet/IP Broadcast Management Device (BBMD)

functionality within the BACnet internetwork.

The BBMD concept requires that a broadcast message

originating on one subnet be encapsulated into a

directed message and sent to all remote subnets since

these directed messages will pass through IP routers.

Once the encapsulated messages are received on the

remote subnets, a BBMD device will decode the

message and resend it on its local subnet as a

broadcast message. Therefore it would appear that a

BBMD device must be present on each subnet in order

to provide this encoding and decoding function.

However, this is not the case if all the BACnet/IP

devices support Foreign Device Registration (FDR). At

a minimum, one BBMD device is required to be located

on one of the subnets with FDR devices registering to

this one BBMD. This is what is shown in the example

with a BAS Router providing BBMD functionality while

allowing for foreign devices registration. Notice that

connecting to a BACnet MS/TP network is an option.

Application #3 — Cascaded Routers for Additional Isolation

For increased security and isolation, IP routers can be

cascaded. Make sure that each LAN-side subnet

address is unique when cascading IP routers. The

left-most IP router can have its WAN-side IP address

assigned using DHCP client or by using static IP

address assignment.

The illustration shows a pair of EIPR routers, but the

right-most router could also be some other type of

router — perhaps one already existing in the business

system — because the EIPR supports standard

Internet protocols.

Application #4 — Limiting BACnet Trafc

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Contemporary-control-systems EIPR Wired/Wireless VPN Router Application Guide Uživatelský manuál Strana 8