Hi all!
Quoting Vinod Anthony Joseph Cherunni (vac@dsqworld.com):
> 1. In a Frame-Relay network, If a router interface / sub-interface is
> configured as "point-multipoint". I have noticed that the DLCI address is
> not mentioned. Does it mean that the FRAD will recieve information on the
> local as well as remote DLCI information on its associated PVC's using the
> LMI interface.
The router will be receiving information on the local DLCIs and
their status via the LMI. Together with Inverse ARP it can discover
the IP (and other) addresses of its neighbours and on which DLCI
they reside.
> Also in a hub spoke topology wherein multiple branch offices are connected
> & to the
> central office, Could a single interface on the central office router be
> associated with multiple PVC's to the branch offices, wherein the
> interface would be configured in multipoint mode.
Yes. IP (and other) addresses can be learned through Inverse ARP or
through static mapping.
> 2. Why are "point-point" interfaces configured explicitedly with the local
> DLCI address. Why is it so?
Inverse ARP makes no sense on point-to-point interfaces because
their could be ambiguities. So the DLCI must be configured
statically.
> 3. On a point-Multipoint interface with connections to more than one
> destination, How does the OSPF adjacency form. Is it similar to a
> broadcast interface, wherein after the InARP process, hello packets are
> replicated to the respective remote IP addresses of the remote routers,
> which are discovered through the InARP process.
> 4. I have heard that OSPF neighbors have to be configured manually in an
> NBMA network. How is this network different from using Frame-Relay in
> either point-point or point-multipoint mode.
Without any extra configuration frame-relay (with Inverse ARP
enabled or static maps with the broadcast keyword) is handled like
any other broadcast capable interface. In particular a DR and BDR
is elected. This can lead to problems when the network is not fully
meshed as the DR and BDR need access to every other attached router
and vice versa. It might be possible to control the DR and BDR
election process in such a way that the former sentence is true even
for a partially meshed network but this has to be done with care and
will lead to problems when certain links fail.
If you configure the network as point-to-multipoint and also
configure your OSPF as "point-to-multipoint" then OSPF will
interpret the interface as a group of point-to-point interfaces and
will handle them just fine. This assumes that broadcast is enabled.
You only need to configure OSPF neighbour commands when you disable
the broadcast capability.
> 5. I know that DLCI's have only local significance, Now in a large
> Frame-Relay network, For e.g. Customer 1 is associated with a local DLCI
> number 1 conected to Frame-Relay switch 1. Now if the other end of the PVC
> is numbered as follows DLCI number 2 connected to Frame-Relay switch 2.
> Now assume the connection between Frame-Relay switch 1 & 2 is via another
> switch called 3. If switch 3 has a DLCI associated with it called 2. What
> would happen if switch 1 is forwarding traffic destined to remote DLCI 2
> which belongs to switch 2. Now since switch 3 is the transit point, What
> would happen when the traffic reaches switch 3, Will it forward it to its
> locally associated DLCI 2 or will it pass it on to the switch 2 which is
> the actual destination.
DLCIs have only local significance and as such may change.
Furthermore I think that the switch does not only account for the
incoming DLCI in his switching decision but for the pair (incoming
port, incoming DLCI). So there is no ambiguity.
> 6. I understand that many FR switches support layer 2 routing, Now FR
> switching is based on static entries such as "Incoming port / Incoming
> DLCI switched to Outgoing port / Outgoing DLCI".
> Now if a particular path connected to outgoing port, How will the switch
> reroute the traffic, Just trying to associate the switching technique to
> normal routing, where rerouting is only possible in the case of Dynamic
> routing, & not static tables.
Switching around failed paths is only possible by using some dynamic
mechanism. I don't really know what kinds of dynamic frame relay
switching there are. If the underlying transport would be ATM, I'd
assume that some form of PNNI is used.
Lars.
-- Lars Fenneberg, lf@elemental.net (private), lf@mcs-cityline.net (work)
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