Difference between revisions of "I-Am-Router-To-Network"

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Additionally, I-Am-Router-To-Network messages must always use a [[BACnet Broadcast|Global Broadcast]]. The reasoning is as follows.  
 
Additionally, I-Am-Router-To-Network messages must always use a [[BACnet Broadcast|Global Broadcast]]. The reasoning is as follows.  
 
# 6.4.1 of the specification states "It shall always be transmitted with a broadcast [[MAC Address]]".  
 
# 6.4.1 of the specification states "It shall always be transmitted with a broadcast [[MAC Address]]".  
 +
## We assume "Broadcast MAC Address" implies the directly connected MAC Address.
 
# Figure 6-5 shows clearly a routed "Who-Is-Router-To-Network"
 
# Figure 6-5 shows clearly a routed "Who-Is-Router-To-Network"
  
The ONLY way to get a (required) broadcast back to the (routed) [[Who-Is-Router-To-Network]] requesting node is via a Global or Directed Broadcast. Since we assume the intent of broadcasting this message is to update all the router tables, then a [[BACnet Broadcast|Directed Broadcast]] seems in conflict, and by a process of elimination it seems the only option we are left with is a [[BACnet Broadcast|Global Broadcast]].
+
The ONLY way to get a (required) broadcast back to the (routed) [[Who-Is-Router-To-Network]] requesting node is via a Global or Directed Broadcast.
 +
 
 +
Additionally, since we assume the intent of broadcasting this message is to update all the router tables, then a [[BACnet Broadcast|Directed Broadcast]] seems in conflict, and by a process of elimination it seems the only option we are left with is a [[BACnet Broadcast|Global Broadcast]].  
  
  

Revision as of 15:14, 19 August 2018

Section 6.4.2 Page 54


Router responds with a list of Network Numbers it can provide access to.


If the Who-Is-Router-To-Network has no networks in the query, then the I-Am-Router-To-Network shall contain all Networks accessible from this router EXCEPT the networks that are connected to the router port that the Who-Is-Router-To-Network arrived on. See Section 6.6.3.2 pg 60.


Always transmitted with a broadcast MAC address.




From the specification: In the event a router receives multiple I-Am-Router-To-Network messages pertaining to the same network, the router shall assume that each new I-Am-Router-To-Network message represents a modification in the system configuration and shall update its routing information. If the router has an established PTP connection (see Clause 10) that conflicts with this new information, the PTP connection shall be terminated using the disconnect procedures defined in Clause 10. Thus the last message received shall take precedence over all previous messages.


This means another, misconfigured router can poach a Network Number from your router. You are not allowed to 'lock' your Network Number, but should consider a warning to the user/System Integrator that this has happened.




Additionally, I-Am-Router-To-Network messages must always use a Global Broadcast. The reasoning is as follows.

  1. 6.4.1 of the specification states "It shall always be transmitted with a broadcast MAC Address".
    1. We assume "Broadcast MAC Address" implies the directly connected MAC Address.
  2. Figure 6-5 shows clearly a routed "Who-Is-Router-To-Network"

The ONLY way to get a (required) broadcast back to the (routed) Who-Is-Router-To-Network requesting node is via a Global or Directed Broadcast.

Additionally, since we assume the intent of broadcasting this message is to update all the router tables, then a Directed Broadcast seems in conflict, and by a process of elimination it seems the only option we are left with is a Global Broadcast.




See other Network Layer Messages.


I-Am-Router-To-Network NSDU
Octets Description Function Notes
1 01 I-Am-Router-To-Network
2 Connected DNET Specifies directly connected DNETs
... Repeated ... according to the number of ports in the Router.


Keyword List
APDU BBMD BVLC BVLL DADR DNET Encoding I-Am LSAP MAC NPCI NPDU NSAP NSDU SA SADR SNET

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