From: Adel Abushaev (adel@netmasterclass.net)
Date: Fri Mar 05 2004 - 22:08:12 GMT-3
You may use multicast helper-maps, and configure directed broadcast to be
encapsulated into multicast and decapsulated on the other side. You will need
to join multicast-side interface to multicast groups, and configure in- and
out- broadcast-multicast and multicast-broadcast helper maps respectively on
both sides, as well as ip forward-protocol for your udp traffic.
This is an article I have found a long time ago on the network, however, that
host is down now, so I am copy-pasting it here from
the backup. Please note that at the end it says that interface will be joined
to mcast group automatically. It doesn't happen most
of the times. Join it manually if your IOS doesn't generate ip igmp join
command for you.
The following is an example which illustrates the use of the helper-map
command at the first-hop and the last-hop, to convert
a broadcast stream directed to port 2000 to a multicast stream and back.
On the first hop router
-----------------------
The following example converts broadcast streams to port 2000
to a multicast stream(G = 224.5.5.5)
int < ... > /* incoming interface of broadcast stream */
ip multicast helper-map broadcast 224.5.5.5 101
ip pim dense
.....
ip forward-protocol udp 2000
access-list 101 permit udp any any eq 2000
access-list 101 deny udp any any
On the last hop router
---------------------
int <...> /* incoming interface of multicast stream */
ip multicast helper-map 224.5.5.5 178.21.34.255 101
ip pim dense
.....
ip forward-protocol udp 2000
access-list 101 permit udp any any eq 2000
access-list 101 deny udp any any
Note:
o Configuring the multicast helper map command (to convert multicast to
broadcast) will also automatically configure "ip igmp join-group <group>"
on the interface. The router must be joined to the multicast group to
be translated to a broadcast address.
o In Cisco IOS 12.0, it is necessary to configure the interface command
"ip directed-broadcast" along with helper-map command. By default,
it is turned off.
HTH,
Adel Abouchaev
CCIE# 12037, MCSE
http://www.netmasterclass.net
----- Original Message -----
From: "Richard Dumoulin" <richard.dumoulin@vanco.es>
To: "Kenneth Wygand" <KWygand@customonline.com>; <Scott>; "Tyson C"
<tyson.scott@hp.com>; <ccielab@groupstudy.com>
Sent: Friday, March 05, 2004 7:56 PM
Subject: RE: Forwarding UDP Broadcasts (not all-1's)
> To me it seems that what you want is bridging. Just configure bridge-group
1
> on all interfaces and delete the ip addresses,
>
> --Richard
>
> -----Mensaje original-----
> De: Kenneth Wygand [mailto:KWygand@customonline.com]
> Enviado el: sC!bado, 06 de marzo de 2004 1:47
> Para: Scott, Tyson C; ccielab@groupstudy.com
> Asunto: RE: Forwarding UDP Broadcasts (not all-1's)
>
>
> Scott,
>
> Thanks for the update. I probably should've been a bit clearer:
>
> Say I have the following topology
>
> [192.1.1.0/24] (E0--R1--S0) ===T1 link=== (S0--R2--E0) [192.2.2.0/24]
>
> Say I have a workstation with address 192.1.1.100 with an application that
> broadcasts UDP packets to locate services on the local subnet. Say the UDP
> packet is destination port 1234 and is a directed network broadcast but for
> the LOCAL NETWORK (192.1.1.255/24). I want this UDP network broadcast to
> reach a workstation on the 192.2.2.0/24 subnet (say 192.2.2.100). So
> essentially I want R1 to take that network broadcast and forward it to
every
> attached router (in this case, R2 - possibly by converting it to an all-1's
> broadcast). Then I want R2 to forward it to all attached routers and all
> local LAN interfaces, so it spills onto the 192.2.2.0/24 network so the
> workstation sitting at 192.2.2.100 receives the broadcast.
>
> Maybe I need to enable DLSW or something, but I have so many LAN segments
> that it would be a much cleaner solution if I could do something like IP
> FORWARD-PROTOCOL UDP 1234.
>
> Any thoughts? Maybe I just need to run "IP directed-broadcast" on E0
> because I think it is currently turned off for security purposes.
>
> Any suggestions are welcome. Thanks in advance,
> Ken
>
> -----Original Message-----
> From: Scott, Tyson C [mailto:tyson.scott@hp.com]
> Sent: Fri 3/5/2004 7:35 PM
> To: Kenneth Wygand
> Cc:
> Subject: RE: Forwarding UDP Broadcasts (not all-1's)
>
>
>
> Thank you
>
>
> -----Original Message-----
> From: Chen Kwong Wai William [mailto:kwchen05@hotmail.com]
> Sent: Friday, March 05, 2004 12:38 PM
> To: Scott, Tyson C
> Subject: Re: ip multicast helper-map - ip directed broadcast
>
> Hi Scott,
>
> The command "ip directed-broadcast" in DocCD is: "To enable the
> translation of a directed broadcast to physical broadcasts" amd also
> it
> states:
>
> =======
> A router that is not directly connected to its destination subnet
> forwards an IP directed broadcast in the same way it would forward
> unicast IP packets destined to a host on that subnet. When a
> directed
> broadcast packet reaches a router that is directly connected to its
> destination subnet, that packet is "exploded" as a broadcast on the
> destination subnet. The destination address in the IP header of the
> packet is rewritten to the configured IP broadcast address for the
> subnet, and the packet is sent as a link-layer broadcast. The ip
> directed-broadcast interface command controls the explosion of
> directed
> broadcasts when they reach their target subnets. The command affects
> only the final transmission of the directed broadcast on its
> ultimate
> destination subnet. It does not affect the transit unicast routing
> of IP
> directed broadcasts.
>
> ======
>
> Therefore, the directed-broadcast command only should be enabled
> on
> the interface connected to the destination subnet. For example,
>
> 192.168.1.1 -E0- (RouterA) -E1- 192.168.2.1
> Then E0 will be the inbound and E1 as the final destination of
> the
> directed-broadcast 192.168.2.255.
>
> Now, if RouterA receives a packet to 192.168.2.255 on E0, RouterA
> will forward it to 192.168.2.1 no matter whether "ip
> directed-broadcast"
> is enable on this interface or not. However, when the packet reaches
> E1,
> then RouterA will drop the packet if E1 has "no ip
> directed-broadcast",
> but will explode as a physical broadcast (255.255.255.255) if E1
> has
> "directed-broadcast".
>
> Therefore, I believe that "directed-broadcast" is only need to be
> enable on the interface where the broadcast will be finally sent to
> (i.e. the outbound interface).
>
> Best Regards,
> William Chen.
>
> ----- Original Message -----
> From: "Scott, Tyson C" <tyson.scott@hp.com>
> To: "William Chen" <kwchen05@hotmail.com>; <braet_kamiel@nl.ibm.com>
> Sent: Friday, March 05, 2004 8:36 PM
> Subject: RE: ip multicast helper-map - ip directed broadcast
>
>
> You are correct my broadcast statement is incorrect. It should be
> 10.3.3.255 PIM is not required on the Ethernet segments since it is
> being re-encapsulated into broadcast at the end and it starts as a
> broadcast. But you are going to be running PIM across the WAN and
> not on
> the Ethernet? What client is going to join a multicast group on the
> WAN?
>
> Here is why I believe you need ip directed-broadcast on both the
> Ethernet interfaces. When a broadcast is received on an interface
> it is
> automatically dropped by the router it does not forward it on when
> it is
> inbound or outbound without this statement. The router would drop
> the
> broadcast before it ever goes through the process of mapping the
> multicast from the broadcast. At least this is how I understood it
> when
> it was explained to me. I have not tested it with a packet
> generated to
> verify what has been told to me. It does make logical sense to me
> from
> my understanding of how other processes work in the IOS but who ever
> said that the code writers for IOS are always logical.
>
>
> -----Original Message-----
> From: William Chen [mailto:kwchen05@hotmail.com]
> Sent: Thursday, March 04, 2004 11:09 PM
> To: Scott, Tyson C; braet_kamiel@nl.ibm.com
> Subject: Re: ip multicast helper-map - ip directed broadcast
>
> Dear scott,
>
> Just find maybe you make some typo in your example, see below:
>
> Best Regards,
> William Chen
>
> > Here is an example of how to do it. You have a broadcast you want
> > forwarded to another subnet from R1 ethernet0 to R2 Ethernet0 and
> the
> > port of the broadcast is going to be 5959. I think it makes
> better
> > sense seeing a good example than the wrong example that is shown
> on
> the
> > doc CD.
> >
> > e0-R1-s0->s0-R2-e0
> >
> > R1#
> > ip multicast-routing
> > ip forward protocol udp 5959
> > !
> > Interface Ethernet0
> > Ip address 10.1.1.1 255.255.255.0
> > Ip pim dense-mode
> > - enable multicast routing on the interface
> > Ip multicast helper-map broadcast 239.39.39.39 115
> > - map the broadcast to a multicast
> > Ip directed-broadcast
>
> Maybe, you should not to enable directed-broadcast here, because
> you
> don't do any multicast to broadcast in the incoming interface (S0 of
> R1).
>
> > - accept the broadcast defined
> > !
> > interface Serial0
> > ip address 10.2.2.1 255.255.255.0
> > ip pim dense-mode
> > !
> > access-list 115 permit any any eq 5959
> > - define which port you are going to accept as a directed
> broadcast !
> > end
> >
> > R2#
> > ip multicast-routing
> > ip forward protocol udp 5959
> > !
> > Interface Ethernet0
> > Ip address 10.3.3.3 255.255.255.0
> > Ip pim dense-mode
> > - enable multicast routing on the interface
>
> Why to enable multicast here?
>
> > Ip directed-broadcast
> > - accept the broadcast defined
> > !
> > interface Serial0
> > ip address 10.2.2.2 255.255.255.0
> > Ip multicast helper-map 239.39.39.39 10.2.2.255 115
>
> The broadcast address should be 10.3.3.255, coz you are sending
> directed broadcast to E0.
>
> > - map the multicast to a broadcast
> > ip pim dense-mode
> > !
> > access-list 115 permit any any eq 5959
> > !
> > end
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> Kenneth Wygand
> Sent: Friday, March 05, 2004 7:28 PM
> To: ccielab@groupstudy.com
> Subject: Forwarding UDP Broadcasts (not all-1's)
>
> Hi everyone,
>
> If I want to forward (flood) all UDP broadcasts to all subnets
> attached
> to a router, how can this be accomplished? The application
> initiating
> the UDP broadcast is sending out a network broadcast, not an all-1's
> broadcast. So if the application resides on a workstation with a
> 10.0.0.1 address, the UDP broadcast is 10.255.255.255, not
> 255.255.255.255. I want the broadcast to reach all other networks
> attached to the router, say for example, 11.0.0.0, 12.0.0.0 and
> such.
>
> As far as I understand, "IP FORWARD-PROTOCOL UDP xxx" will only
> forward
> all 1's broadcasts and will not convert the network broadcast to an
> all-1's broadcast. Is this correct?
>
> For some reason I'm wondering if a "multicast helper map" can be
> contorted to help accomplish my goal.
>
> Please let me know your opinions, and thank you in advance!
> Ken
>
>
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