Basic OSPF packets

Lets consider this

R1(fa0/0)------R2(fa0/0)

when OSPF protocol is configured only on R1 via "router ospf"  it joins multicast groups 224.0.0.5 and 224.0.0.6 check via

R1#sh ip int f0/0 | in Multicast

  Multicast reserved groups joined: 224.0.0.5 224.0.0.6

Now if other router R2 on this link is not running OSPF it will not join these multicast groups check on R2

R2#sh ip int f0/0 | in Multicast

R2#

So when R1 sends OSPF packets to R2 at multicast destination address of 224.0.0.5 with ip protocol ip 89 check on R2 via

R1#debug ip packets details

*Mar  1 00:17:45.907: IP: s=10.0.0.1 (local), d=224.0.0.5 (FastEthernet0/0), len 76, sending broad/multicast, proto=89

Since R2 does not have layer 2 multicast address corresponding to Layer 3 multicast address 224.0.0.5 because R2 has not joined this group (OSPF is not enabled ). Therefore when these packets arrived on R2's layer 2. It will discard all these packets at this layer. Hence no packets will be shown at layer 3 via

R2#debug ip packets details

R2#

Conclusion: OSPF packets will not be received at R2's network layer 3 because they were already being discarded at R2's layer 2.