From: Petr Lapukhov (petrsoft@gmail.com)
Date: Thu Jun 15 2006 - 09:47:23 ART
As for broadcast address, it may depends on application :) Sometimes
they ask you to use specified broadcast, and alike. Just remember,
even if you put a directed-broadcast into "multicast-helper" it wont be
converted until you put an "ip broadcast-address"
Now for the dense-mode. I agree, there is no particular restiction
to use "dense-mode" here. It's just reflects "flooding" behavior well,
and is more simple to configure, after all ;)
Sparse and Bidir should work fine too, I just remember that I had
problems with source registration in PIM-SM. That was quite some
time ago, and maybe it was just my lazy head and misundestanding,
since it's a regular multicast source, after all :)
One just can't lab all the scenarios, and I preferred to focus on Core
topics :)
Petr
2006/6/15, Pierre-Alex <paguanel@hotmail.com>:
>
> Petr,
>
> What is the logic behind using "multicast-helper" in dense mode rather
> than sparse?
>
> I don't see why dense mode would be more "appropriate".
>
> And also why would you ever want to use a broadcast address different than
> 255.255.255.255 ?
>
> (It would require you to change this on all the routers on your LAN and
> all the hosts and application etc ..)
>
> Thanks.
>
> Pierre-Alex
>
> ----- Original Message -----
> *From:* Petr Lapukhov <petrsoft@gmail.com>
> *To:* Pierre-Alex <paguanel@hotmail.com>
> *Cc:* ccielab@groupstudy.com
> *Sent:* Thursday, June 15, 2006 12:57 PM
> *Subject:* Re: analysis: multicast-helper map and directed broadcast
>
> Pierre,
>
> Usually "multicast-helper" is used with pim-dense mode, so no need
> to register source here. I actually tried to test it with sparse mode,
> had no luck, and dropped my attempts due to the lack of time ;))
>
> Next, if you dont put "ip directed-broadcast"
> and "ip broadcast-address" the router will simply send packets
> to address 255.255.255.255, AFAIR. If you need some specific
> broadcast address, you should configure it.
>
> HTH
> Petr
>
> 2006/6/15, Pierre-Alex <paguanel@hotmail.com>:
> >
> > In the cisco Documentation , on the interface of the last hop router is
> > configured a "directed broacast" statement.
> >
> >
> > http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cr/himc_r/
> > mlt_i1h.htm#wp1075964
> >
> > I have labbed the example WITHOUT this command and the conversion worked
> > properly: my last hop router is sending broadcast.
> >
> > Also I have not enable pim on the outgoing interface of the last hop
> > router as
> > the example, and it is working too.
> >
> > The way I explain theses results is as follows:
> >
> > 1. " By default, IP directed broadcasts are dropped; they are not
> > forwarded.
> > By dropping IP directed broadcasts, routers are less susceptible to
> > denial-of-service attacks."
> > http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/np1_c/
> >
> > 1cprt2/1cipadr.htm#wp4443
> >
> > In this case, the router is not receiving directed broadcast. It is
> > receiving
> > a multicast flow from its upstream neighbor, so there is no issue of
> > directed
> > broadcast.
> >
> > 2. When the router transforms the multicast flow it first creates a flow
> > to
> > the directed broadcast address. Since the flow was originated INTERNALLY
> > (by no interface whatsoever), there is no issue of "fowarding a directed
> >
> > broadcast" and therefore no restriction on converting this flow to
> > broadcast.
> > So the router broadcasts its self-created directed broadcast.
> >
> >
> > 3. Regarding enabling multicast on the source I suspect this is
> > necessary so
> > that the first-hop router can create the (S,G) entry, as if it an actual
> > registration had occured. But on the destination I believe it is not
> > necessary , since the whole purpose is to direct traffic to users who
> > are not
> > multicast able.
> >
> > On first-hop router
> >
> > (*, 225.1.1.1), 01:29:02/stopped, RP 150.1.2.2, flags: S
> > Incoming interface: Null, RPF nbr 0.0.0.0
> > Outgoing interface list:
> > Serial0/1, Forward/Sparse, 01:29:02/00:03:18
> >
> > (10.1.2.200, 225.1.1.1), 01:12:28/00:03:29, flags: T
> > Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0
> > Outgoing interface list:
> > Serial0/1, Forward/Sparse, 01:12:28/00:03:18
> >
> >
> > I would appreciate some feedback / comment on my analysis. Working
> > configurations below.
> >
> > Thank You,
> >
> > Pierre-Alex
> >
> > ----------------
> > Diagram:
> > -----------------
> >
> > Server(source)--F0/0--R2----multicast----r3-e0/0--R4(Receiver)
> > The source 10.1.2.200 is sending udp broadcast on dest port 65300
> >
> > -----
> > Configs
> > -------
> >
> > !r2
> >
> >
> > interface FastEthernet0/0
> > ip address 10.1.2.2 255.255.255.0
> > ip pim sparse-mode ! REQUIRED
> > ip multicast helper-map broadcast 225.1.1.1 100 ! REQUIRED: for
> > conversion of
> > broadcast
> > duplex auto
> > speed auto
> >
> > access-list 100 permit udp any any eq 65300
> >
> >
> > ip forward-protocol udp 65300
> > ! REQUIRED: Allows the processing of incoming udp broadcast packets
> >
> >
> > ! r3
> >
> >
> > interface Ethernet0/0
> > ip address dhcp
> > ip multicast helper-map 225.5.5.5 192.168.108.255 100
> > ! I HAVE NOT ENABLED PIM ON THIS INTERFACE
> >
> >
> > R3#sh ip int e 0/0
> > Ethernet0/0 is up, line protocol is up
> > Internet address is 192.168.108.203/24
> > Broadcast address is 255.255.255.255
> > Address determined by DHCP
> > MTU is 1500 bytes
> > Helper address is not set
> > Directed broadcast forwarding is disabled !-----> I HAVE NOT ENABLED
> > DIRECTED BROADCASTS
> > Multicast reserved groups joined: 224.0.0.1 224.0.0.2 224.0.0.22
> >
> >
> > ! r4 (receiver)
> >
> >
> > interface Ethernet0/0
> > ip address dhcp
> > ip access-group 100 in
> > half-duplex
> >
> > access-list 100 permit udp any any eq 65300
> > access-list 100 permit ip any any
> >
> > Extended IP access list 100
> > 10 permit udp any any eq 65300 (251180 matches) !!! RECEIVER IS
> > GETTING
> > THE TRAFFIC
> > 20 permit ip any any (48 matches)
> >
> > _______________________________________________________________________
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