From: Rik Guyler (rik@guyler.net)
Date: Thu Jan 29 2009 - 13:05:11 ARST
Very nice summary Rick. MTU must also match on both sides as well or you
can disable the MTU checking. This may be a big one for you to troubleshoot
on your lab so be sure to keep it in mind.
Here's a good link:
<http//www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f0d
.shtml>
Rik
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Rick
Tyrell
Sent: Thursday, January 29, 2009 9:24 AM
To: Brian Spade
Cc: Raghav Bhargava; Cisco certification
Subject: Re: Regarindg OSPF Network type
Raghav, I spent a couple of days taking notes about the different OSPF
network-types. Here is what I came up with:
An adjacency will be formed with routers running OSPF, as long as the
authentication is the same, the stub flag is the same, the area is the same,
and the timers are the same. If we mix and match network types we might need
to modify the timers so we can form an adjacency. This is done with the ip
ospf
hello-interval<http://www.cisco.com/en/US/docs/ios/12_4t/ip_route/command/re
ference/rteospht.html#wp1147542>and
ip
ospf
dead-interval<http://www.cisco.com/en/US/docs/ios/12_4t/ip_route/command/ref
erence/rteospht.html#wp1147272>commands.
You can mix and match network types as long as the network types
involved have the same DR relationship. You can't mix network types that
require a DR with those that don't require a DR.
- For topologies where you have one hub, ensure the hub is the DR or use
a network type that doesn't require a DR
- For topologies that have more than one hub, use a network type that
doesn't require a DR
- In partial mesh topologies, the hubs should use a broadcast frame-relay
map on DLCI's to all connected spokes. This is to stop redundant
broadcasts
- In partial mesh topologies, the spokes should use a broadcast
frame-relay map on DLCI's to the hub only. This is to stop redundant
broadcasts
*Broadcast:*
- Default on Ethernet
- Hello interval 10 seconds
- Dead Interval 40 seconds
- DR/BDR election
- Updates are sent as multicast
- Next hop is not changed and remains the ip address of the originating
router
- The broadcast model over Frame Relay works properly if the *Frame Relay
cloud is fully meshed*. If any permanent virtual circuits (PVCs) are
broken, it can create problems in the OSPF database
*Non-Broadcast: *
- Default on Multipoint interface like Frame-relay
- Hello interval 30 seconds
- Dead Interval 120 seconds
- DR/BDR election
- Updates are sent as unicast
- Neighbor command required on hub router
- Next hop is not changed and remains the ip address of the originating
router
- *Use in smaller FR networks -- Non-broadcast is used where
broadcast/multicast is not feasible. The drawback to this interface type
is
that neighbors must be explicitly configured, which can get to be a
nuisance.*
*Point to Point:*
- Default on HDLC, PPP and Frame-relay Point-to-Point
- Hello Interval 10 seconds
- Dead Interval 40 seconds
- No DR/BDR Election
- Multicast updates to 224.0.0.5
- Next hop address is that of the advertising router
*Point to Multipoint Broadcast: ** *
- Cisco proprietary
- Host routes are added in the routing table
- Hello Interval 30 seconds
- Dead Interval 40 seconds
- No DR/BDR Election
- Multicast updates to 224.0.0.5
- Next hop address is that of the advertising router
- Frame-relay partial mesh
- From Cisco: In a Frame Relay environment, *if Layer 2 is unstable, as
in our example, we do not recommend an OSPF broadcast network-type. Use
OSPF
point-to-multipoint instead*
- *All routers belonging to the same IP subnet are assumed to be directly
reachable. Point-to-multipoint OSPF mode should be used in
partially-meshed
NBMA network.*
*Point to Multipoint Non-Broadcast:*
- Cisco proprietary
- Hello Interval 30 seconds
- Dead Interval 120 seconds
- Frame-relay Partial Mesh
- No DR/BDR Election
- Unicast updates
- Created to allow for the assignment of the cost per neighbor as opposed
to using the interface's cost. This is useful on a multipoint *Frame
Relay* interface where there are two neighbors *advertising* the same
route but the CIRs for the DLCIs to reach each neighbor is different or
these two neighbors that are advertising the same route have different
port speeds to the Frame Relay network. Remember that the cost is based
on your "incoming" interface's bandwidth and not the bandwidth of the
neighbor's interface that connects to you.
On Thu, Jan 29, 2009 at 2:18 AM, Brian Spade <bitkraft@gmail.com> wrote:
> Raghav,
>
> I suggest you read this:
>
> http://www.cisco.com/en/US/docs/ios/11_3/feature/guide/ospfpmp.html
>
> /bs
>
> On Wed, Jan 28, 2009 at 11:14 PM, Raghav Bhargava <
> raghavbhargava12@gmail.com> wrote:
>
> > Hi Experts,
> >
> > In OSPF network types, we have 4 of them namely:-
> >
> > 1. Broadcast.
> > 2. NBMA.
> > 3. Point-to-point
> > 4. Point-to-multipoint.
> >
> > My queries are:-
> >
> > 1---> What is the default for Point -to - multipoint. Is it Broadcast
> > in nature. I could be wrong.
> > 2---> If it is Broadcast by default , then does it acquires all the
> > characteristics of Broadcast Network Type like Dr and BDR. Sending
> > Multicast etc etc.
> >
> > Please can someone explain Point-to-multipoint ??
> >
> > --
> > Warm Regards
> > Raghav
> >
> >
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> >
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