RE: multicast helper map and ip directed-broadcast

Ip directed-broadcast is configured on R4, F0/0 and "debug ip udp" shows the
following:

R5:

*Mar 1 12:16:07.528: UDP: rcvd src=10.1.12.1(520),
dst=255.255.255.255(520), length=32

R4:

*Mar 1 12:18:33.744: UDP: rcvd src=10.1.12.1(520), dst=224.1.1.1(520),
length=32

*Mar 1 12:18:33.748: UDP: forwarded broadcast 520 from 10.1.12.1 to
255.255.255.255 on FastEthernet0/0

No directed broadcast in this output. However R4 needs to be configured with
"ip directed-broadcast" without it R5 will not receive anything. Now I am
really confused...

Do I understand correctly that I should see "dst=10.1.45.255" in debug ?

From: Narbik Kocharians [mailto:narbikk_at_gmail.com]
Sent: 12-Oct-10 11:07
To: Jack Router
Subject: Re: multicast helper map and ip directed-broadcast

Because the last router takes the Mcast traffic and converts it and sends it
as a directed broadcast, and we know that Cisco routers do not allow
directed broadcast unless specifically configured.

On Tue, Oct 12, 2010 at 7:23 AM, Jack Router <pan.router_at_gmail.com> wrote:

Hello Experts,

I have a question regarding directed broadcast in multicast helper map: Why
"ip directed-broadcast" is needed on R4 int F0/0? It does not work without
it.
For those who use Narbik workbooks it is about Vol2, Multicast, Lab 10.

Topology:

R1(F0/0)---(F0/0)R2--frame--R3--frame--R4(F0/0)---(F0/0)R5

Multicast runs on R2, R3, R4
R1 is configured to send broadcast updates.

When I debug ip packets on R5 I see that R5 receives RIP updates from R1
with destination address of 255.255.255.255. There is no 10.1.45.255 in the
debug:

*Mar 1 10:31:30.717: IP: s=10.1.12.1 (FastEthernet0/0), d=255.255.255.255,
len 52, rcvd 2

Why then ip directed-broadcast is needed in R4 F0/0 ? What it does ?

Thanks,

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Received on Tue Oct 12 2010 - 12:07:07 ART