From: Adam Crisp (adam.crisp@totalise.co.uk)
Date: Fri Oct 11 2002 - 10:03:52 GMT-3
Hi Dave,
I have just set up my Lab the same as yours.
I started with three routers each with Frame relay Multipoint interfaces
I then changed one of the spoke routers so that is was configured as a frame
relay point to point interface, the same as yours.
I only bothered to change one of my routers.
I think you may be confusing Frame Relay network interface types and OSPF
network types.
i.e.Frame-relay point-to-point, point-to-multipoint interfaces
and
ospf network types - in this case point-to-point and non broadcast.
FrameRelay
Essentialy a point to point interface is a multipoint interface that only
supports one DLCI (please don't pick on me about this)
You configure a point-to-point interface and give it a DLCI and it should
work.
A point-to-multipoint interface supports one or multiple DLCIs.
You need to use frame-relay maps or invarse arping to map L3 addreses to
datalink...
OSPF,
In order to form OSPF adjacencies the OSPF_Network types need to match.
(You may see posts to the group which people sucsessfully manage to form
adjacencies by changing timers - but don't go there! ;-( )
There are for OSPF_Network types:
1. Broadcast - uses DR's
2. Non Broadcast - uses DR's
3. Point-to-Multipoint - especially made for frame-relay NBMA and has some
benefits over 1 & 2
4. Point to Point - no good on NBMA unless you only have two routers
With 1 & 2 above the hub needs to be the DR and the Spokes must not be a
DR/BDR - (use ip ospf priority 0 on spoke interface)
This is how OSPF gets around split-horizon, by the DR generating a type 3
lsa....
The added benefit of using option 3 above is that you can configure
different OSPF costs per spoke, otherwise cost is calculated from the
bandwidth statement
Good luck
Adam
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Dave Cooper
Sent: 11 October 2002 13:27
To: CCIE
Subject: OSPF NBMA - Hub and Spokes
Hi
r1-----r2
|
|-----r3
- Version 12.1(11.6). All interfaces are frame relay
sub interfaces.
- OSPF Area=1 for all interfaces
- r1 interface is p-2-m. Has frame-r map to r2 & r3
(have added broadcast too in the map command)
- r2 is p-2-p. Has frame-r interface-dlci going to r1
(On 12.1 frame-r map is not allowed on p-2-p)
- r3 is p-2-p. Has frame-r interface-dlci going to r1
(frame-r map is not allowed)
- I can ping from every router to every other router.
Problem 1
=========
On r1 - sh ip ospf inter shows interface as NBMA. Also
I've added nei as r1 and r3. OSPF pri = 100
On r2 - sh ip ospf inter shows interface as p-2-p.I
didn't add neibhor.
On r3 - sh ip ospf inter shows interface as p-2-p.I
didn't add neibhor.
I can't form adjacency between r1--r2 & r1--r3.
However if I make r2 & r3 interface as NBMA and add r1
as neighbor (on both r2 & r3), adj. is formed.
I think, few days back I saw email (if hub is nbma,
spoke need not be NBMA) which was contrary to what I'm
seeing.
Should we have hub=NBMA && spoke(s)=NBMA ??
Problem 2
=========
further,
On r2 - I add r3 as neighbor
On r3 - I add r2 as neighbor
Adj is not formed, even though r2 & r3 can ping each
other. I keep getting TTL exceed drop messages on R1
(source=r2, dest=r3 and vice versa)
Why are pings going through but adj is not formed ??
Am I missing something really basic here ?
thanks
Dave
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