Suppose I have one ospf network where two multicast group exists. And some routers is ospf which belongs to one group or multiple group (Like: routers E, H) and router is layer3 router (Like: routers A, C, K), not ospf router. Like given below:
I divided the whole network into two parts Multicastgroup 1 and Multicastgroup 2.Like given below:
I have some confusions which are given below:
Confusion 1:: We know that all routers which belongs to same group one multicast address. So my question is routers which belongs to different subnets, but they are also using same multicast address? For example the adjacent link between routers H and I belongs to one subnet and the adjacent link between routers I and J belongs to another subnet , but they are using one multicast address i. e. belongs to same group. Am I correct?
Confusion 2:: The adjacent link between two routers should belongs to same group? I mean the adjacent link between two routers, is there possible one interface of adjacent link belongs to one group and another interface belongs to another group or is there possible one interface belongs to any group and another is layer3 interface?
Confusion 3:: We see that in routers A, C, K don't running routing protocol ospf. Suppose one router belongs to group 1,say J floods the routing protocol information when that information comes into interfaces of layer3 routers A, C, K they just route routing protocol information and don't exchange the routing protocol information because layer3 routers A, C, K running upto layer3 but routing protocol information is application database? Am I correct?
Confusion 4:: When one router interface belongs to one multicastgroup, when that interface get another multicastgroup routing protocol information, both exchange the routing protocol information? I mean group1 router interface could exchange the routing protocol information with group2 router interface?
Confusion 5:: Router one interface could run more than one than one routing protocol? I mean router one interface could belongs to both multicast groups?
Best Answer
OSPF uses a link-local multicast group that does not cross a router. Each OSPF multicast is confined to a single link.
There is nothing about your diagrams that would have an OSPF multicast on more than two routers. In fact, it would be a best practice to use unicast for your diagram.
Every interface on a router would use the OSPF multicast groups for all routers (
224.0.0.5for IPv4,FF02::5for IPv6) and DR/BDR (224.0.0.6for IPv4,FF02::6for IPv6). Those multicasts are confined to the link on which they are originate, and are not propagated across a router to other links.