Subject: Directed Broadcasts in CIDR domain..

From: Anand Kumar Goenka <[email-masked]>
Date: Tue, 10 Feb 1998 12:02:22 +0530

Hi All,
      
     I am referring to sec 5.3.5 of RFC-1812-"Router Specification"
According to this RFC "All subnet directed broadcast" is meaningless in
CIDR routing domain and also "Network-prefix directed broadcast" and
"subnet Directed
Broadcast" has same meaning in CIDR routing domain.
   But there is problem in the way a CIDR capable ruoter can(or should)
interprate an incomming directed broadcast.
Scenario Description:
      Suppose router has the routing table entries for following 3
networks..
      
        1.  150.1.10.0/23
        2.  150.1.16.0/23
        3.  150.1.8.0/21

and the router received a packet with destination address 150.1.15.255 .
Considering the above routing table entries router can have following
directed 
broadcast interpretation for this packet.

       a) A directed broadcast to 150.1.8.0/21 - in this case router has
to forward the packet to both 150.1.10.0/23 and 150.1.16.0/23
       b) A directed broadcast to 150.1.16.0/23 - in this case router
has to forward the packet only to 150.1.16.0/23
       
Question - which one of the above interpretation is correct ?

An early reply will be helpfull..

Thanks & Regards,

Anand Kumar Goenka,
Motorola India Electronics Ltd,
Email: [email-masked]

---

From: Fred Baker <[email-masked]>
Date: Tue, 10 Feb 1998 07:49:35 -0800

>Question - which one of the above interpretation is correct ?

since the address is ambiguous, I would think (speaking for myself and
nobody else) that the most robust interpretation is (a).

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