I posted similar question about three/four weeks ago. Got some answers but still have doubt. Hope someone can shed some light on this question.
Section 9.5. of RFC 2328 : Quote On broadcast networks and physical point-to-point networks, Hello packets are sent every HelloInterval seconds to the IP multicast address AllSPFRouters. On virtual links, Hello packets are sent as unicasts (addresses directly to the other end of the virtual link) every HelloInterval seconds. On Point-to-Multipoint networks, separate Hello packets are sent to each attached neighbor every HelloInterval seconds. Unquote The way I interpret the statement "On Point-to-Multipoint networks, separate Hello packets are sent to each attached neighbor every HelloInterval seconds" is that the Hello packets are unicasted. The Cisco's IOS interface subcomment 'ip ospf network point-to-multipoint' by default configures the network to 'broadcast'. But does that mean the packets, Hello packets and others, are now multicasted as a result of the interface subcomment 'ip ospf network point-to-multipoint' ? If this is the case then this configured 'point-to-multipoint' network is no longer conforming to RFC 2328 ? I was looking at a Tech Notes paper from Cisco : http://www.cisco.com/warp/public/104/20.html. This paper describs a way to resolve the problem of OSPF routers cannot form adjacency on a PRI, BRI or Dialer interface. This 'Tech Note' says the problem is due to the fact that OSPF uses multicast packets for point-to-point network type and routers are getting packets meant for other router. Quote According to RFC 2328 section 8.1, OSPF sends a multicast packet for a point-to-point network type even after the interface achieves the 2-way state. Since RTR-A is trying to form adjacencies with both RTR-B and RTR-C, RTR-B receives DBD packets meant for RTR-C and RTR-C receives DBD packets meant for RTR-B. To solve this problem, change the network type on all routers to point-to-multipoint. This changes the behavior of OSPF to send unicast packet after the 2-way state. Now RTR-B receives only packets destined for itself and RTR-C receives packets destined for itself. Changing the network-type in this way ensures that the OSPF router will form adjacency on a PRI, BRI, or dialer interface. Unquote The way I understand this Tech Note, the interface subcomment 'ip ospf network point-to-multipoint' does not change the way how OSPF packets are sent - they are still unicasted. What is the definitive answer to this question then ? Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=23766&t=23655 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
