Welcome to the world of OSPF. I trust you are prepared for a long and
rewarding journey through the maze of possibilities.
Much OSPF study is best done with a router at hand so you can set up various
things and look and see how the protocol behaves.
page 417: taken out of context. If you check how OSPF defaults on an NMBA
interface or multipoint subinterface you will find the default is NMBA
Serial2/3.1 is down, line protocol is down
Internet Address 99.99.99.99/24, Area 0
Process ID 1000, Router ID 192.168.1.1, Network Type NON_BROADCAST, Cost:
48
Transmit Delay is 1 sec, State DOWN, Priority 1
No designated router on this network
No backup designated router on this network
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
one can change this interface to an OSPF point-to-multipoint by using the
interface command ip ospf network point-to-multipoint, at which time you get
Serial2/3.1 is down, line protocol is down
Internet Address 99.99.99.99/24, Area 0
Process ID 1000, Router ID 192.168.1.1, Network Type POINT_TO_MULTIPOINT,
Cost
: 48
Transmit Delay is 1 sec, State DOWN,
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
if you check RFC 2328, you will find that behaviour in terms of LSA's is
different for both of these cases. As are the configuration contortions you
must now perform.
a couple of more quotes from the RFC are found below
best wishes in your OSPF pursuits
Chuck
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Alex Lee
Sent: Sunday, September 16, 2001 9:30 AM
To: [EMAIL PROTECTED]
Subject: Re: OSPF packets, point-to-multipoint [7:20115]
Group,
Can someone help me to understand or point me to a link so that I can get a
definitive answer. Thanks.
Routing TCP/IP, Vol. 1, Jeff Doyle :
(a) Page # 417, 'Point-to-multipoint networks are a special configuration
...... because the network are seen as point-to-point links, OSPF packets
are multicast'.
(b) Page # 451, 'On point-to-multipoint and virtual link networks, updates
are unicasted to the interface addresses of adjacent neighbors'.
(c) Page # 561, 'The OSPF point-to-multipoint network type treats the
underlying as a collection of point-to-point links ......., and OSPF packets
are multicast to the neighbor.'
----------
CL inserted:
>From the RFC:
12.4.1.4. Describing Point-to-MultiPoint interfaces
For operational Point-to-MultiPoint interfaces, one or
more link descriptions are added to the router-LSA as
follows:
o A single Type 3 link (stub network) is added with
Link ID set to the router's own IP interface
address, Link Data set to the mask 0xffffffff
(indicating a host route), and cost set to 0.
o For each fully adjacent neighbor associated with the
interface, add an additional Type 1 link (point-to-
point) with Link ID set to the Router ID of the
neighboring router, Link Data set to the IP
interface address and cost equal to the interface's
configured output cost.
And also:
The IP destination address for the packet is selected as
follows. On physical point-to-point networks, the IP
destination is always set to the address AllSPFRouters. On all
other network types (including virtual links), the majority of
OSPF packets are sent as unicasts, i.e., sent directly to the
other end of the adjacency. In this case, the IP destination is
just the Neighbor IP address associated with the other end of
the adjacency (see Section 10). The only packets not sent as
unicasts are on broadcast networks; on these networks Hello
packets are sent to the multicast destination AllSPFRouters, the
Designated Router and its Backup send both Link State Update
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=20117&t=20115
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