Since the neighbor is not manually configured with a neighbor command in this scenario, the OSPF process won't know the unicast address and thus it will use multicast (instead of broadcast which was used in RIPv.1 for example).
The router doesn't need to assume or guess what the neighbor address is. It simply needs to use the multicast address as the destination address, push the packet through the serial line and sure enough the packet will make it to the neighbor, which will know for sure the packet is destined for it.
Why should the router guess the neighbor IP address. What if a /24 is used on that link? An worse what if ip unnumbered is used on that link? Using the multicast address is a simple way to alleviate all that.
Hope this helps,
Harold Ritter Sr. Technical Leader CCIE 4168 (R&S, SP) email@example.com México móvil: +52 1 55 8312 4915 Cisco México Paseo de la Reforma 222 Piso 19 Cuauhtémoc, Juárez Ciudad de México, 06600 México
I guess that the answer to your question is divided in to 2 parts, the first is, this is how the algorithm is written and the second is because point-to-point link doesn't always obey this rule, as some times for example we use unnumbered interfaces and thus using multicast would be the generalized solution.
This is actually a pretty cool feature, i didn't even know it existed until I was looking for a solution to advertise a subnet (prefix in BGP talk), only if a certain condition existed. This is exactly what conditional advertisements does
j ai une question j ai achete un routeur cisco 887VA-k9 , je le configuré avec la configuration ci- dessous
si je le lier avec mon pc portable sur l un de ses ports directement ça marche toute est bien ( la connexion internet + m...
Attached policy provides CLI access to the Cisco 4G router over text messaging. Two files are in the attached .tar file:
2. PDF with instructions on how to load and use the .tcl file.