Re: NBMA ....IGP DOUBTS

 How the Router Sends Broadcast and Multicast Packets in a Frame Relay
Network:

When nonbroadcast multiaccess (NBMA) networks such as Frame Relay networks
need to send broadcast or multicast data packets on a main interface,
routers perform a pseudobroadcast. This process uses the broadcast queue,
which operates independently of the normal interface queue (see Figure 4).
The broadcast queue is commonly configured to prevent routing updates from
being dropped from the queue.

http://www.cisco.com/en/US/docs/ios/solutions_docs/ip_multicast/White_papers/frm_rlay.html#wp1023415

The Keyword broadcast
The broadcast keyword provides two functions: it forwards broadcasts when
multicasting is not enabled, and it simplifies the configuration of Open
Shortest Path First (OSPF) for non-broadcast networks that use Frame Relay.
The broadcast keyword might also be required for some routing protocols --
for example, AppleTalk -- that depend on regular routing table updates,
especially when the router at the remote end is waiting for a routing update
packet to arrive before adding the route.

By requiring selection of a designated router, OSPF treats a non-broadcast,
multi-access network such as Frame Relay in much the same way as it treats a
broadcast network. In previous releases, this required manual assignment in
the OSPF configuration using the neighbor interface router command. When the
frame-relay map command is included in the configuration with the broadcast
keyword, and the ip ospf network command (with the broadcast keyword) is
configured, there is no need to configure any neighbors manually. OSPF now
automatically runs over the Frame Relay network as a broadcast network. (See
the ip ospf network interface command for more detail.)

Note: The OSPF broadcast mechanism assumes that IP class D addresses are
never used for regular traffic over Frame Relay.

Example
The following example maps the destination IP address 172.16.123.1 to DLCI
100:
interface serial 0
 frame-relay map IP 172.16.123.1 100 broadcast OSPF uses DLCI 100 to
broadcast updates.

http://www.cisco.com/en/US/tech/tk713/tk237/technologies_tech_note09186a008014f8a7.shtml#broadcastkey

--
Garry L. Baker
"With sufficient thrust, pigs fly just fine..." - RFC 1925
On Sat, Jul 16, 2011 at 8:35 PM, George Tosh <gtosh_at_aeneas.net> wrote:
> To answer question number 3, the broadcast keyword as I understand it,
> instructs the router to forward broadcast/multicast traffic to the other
> router as unicast traffic. This allows routing protocols to form adjacencies
> without the use of the neighbor statement.
>
> Or at least that's the way I understand it, experts please correct me if
> I'm wrong on this point.
>
>
>
>
> Sent from my iPad
>
> On Jul 16, 2011, at 12:15 PM, marc abel <marcabel_at_gmail.com> wrote:
>
> > NBMA mode deos not support broadcasts by default, so routing protocols
> > that use broadcast/multicast to communicate will not form adjacency.
> > Using frame-relay interface-dlci or the broadcast option on a static
> > frame map gets around this. If you don't have this, then you will need
> > neighbor statements.
> >
> > If you specifiy the OSPF network type as broadcast you are signalling
> > two things. 1. That you expect to elect a DR and 2. That you will be
> > using "fast" timers 10/40 seconds.
> >
> >
> >
> > On Sat, Jul 16, 2011 at 12:02 PM, imran ali <immrccie_at_gmail.com> wrote:
> >> HI experts
> >>
> >> 1 )since NBMA does not support multicast ..then how are we able to form
> >> adjacency on it ..for example rip and eigrp ..just turn the interface on
> and
> >> neighbors will come up .....without any need to configure neighbor
> commands
> >> ... is it that protocol has inbult features that sense underlying frame
> >> relay media and begins unicasting the neighbors as RIP and eigrp dont
> >> require " classical neighbor commands" as required by OSPF ...
> >>
> >>
> >> 2) on  a frame network if we specify OSPF network type as " broadcast"
> does
> >> this turns the frame network that natively dosent support broadcast
> ...to
> >> suddenly start supporting broadcast ....
> >>
> >> 3) whats the funda with " broadcast " key word in frame relay static
> maps
> >> ... whats differce will it create if i dint specify it ...
> >>
> >> my routing protocols will not work if i dint specify it ?
> >>
> >>
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