GroupStudy.com GroupStudy.com - A virtual community of network engineers
 Home  BookStore  StudyNotes  Links  Archives  StudyRooms  HelpWanted  Discounts  Login
Re: Forwarding UDP Broadcasts (not all-1's) posted 03/06/2004
[Chronological Index] [Thread Index] [Top] [Date Prev][Date Next] [Thread Prev][Thread Next]


    Configure bridging and turn on the "ip forward-protocol spanning-tree".


http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipras_r/1rfipadr.htm#1018466

Best Regards,
William Chen

----- Original Message ----- 
From: "Richard Dumoulin" <richard.dumoulin@xxxxxxxx>
To: "Kenneth Wygand" <KWygand@xxxxxxxxxxxxxxxx>; <Scott>; "Tyson C"
<tyson.scott@xxxxxx>; <ccielab@xxxxxxxxxxxxxx>
Sent: Saturday, March 06, 2004 8:56 AM
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@xxxxxxxxxxxxxxxx]
> Enviado el: sC!bado, 06 de marzo de 2004 1:47
> Para: Scott, Tyson C; ccielab@xxxxxxxxxxxxxx
> 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@xxxxxx]
> 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@xxxxxxxxxxx]
> 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@xxxxxx>
> To: "William Chen" <kwchen05@xxxxxxxxxxx>; <braet_kamiel@xxxxxxxxxx>
> 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@xxxxxxxxxxx]
> Sent: Thursday, March 04, 2004 11:09 PM
> To: Scott, Tyson C; braet_kamiel@xxxxxxxxxx
> 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@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On Behalf
> Of
> Kenneth Wygand
> Sent: Friday, March 05, 2004 7:28 PM
> To: ccielab@xxxxxxxxxxxxxx
> 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
>
>
> _______________________________________________________________________
> Please help support GroupStudy by purchasing your study materials
> from:
> http://shop.groupstudy.com
>
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
> _______________________________________________________________________
> Please help support GroupStudy by purchasing your study materials from:
> http://shop.groupstudy.com
>
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
> _______________________________________________________________________
> Please help support GroupStudy by purchasing your study materials from:
> http://shop.groupstudy.com
>
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html