In a practice test for CCNA exam 640-801, the correct answer given to a question re OSPF hop count limitation was that this is unlimited when OSPF is being used on a network. I am confused by this as there is an 8-bit TTL field in the IP datagram header, and this is decremented by 1 by each router traversed. When this TTL count reaches zero the IP packet should be discarded. The max for 8-bit field is 255, so shouldn't there be a hop count limit of 255 for OSPF, and indeed ANY routing protocol ?
When an OSPF router receives an advertisement from a neighbor it will NEVER just relay it. (for one thing the multicast address used by OSPF for advertisements is a link local address which should never be forwarded) The router takes the information from the advertisement, puts it into its link state data base, and then generates a new advertisement reflecting the information.
I do not think that we have articulated it clearly yet, but it seems to me that this whole discussion is confusing the functionality of 2 protocols. There is TTL which is used by the IP protocol to minimize the impact of any packet that happens to get into a routing loop. And there is hop count which is used by some routing protocols to determine if something is so far away that it should no longer be advertised. These are 2 different functions in 2 different protocols and we should not treat them as if they were the same.
So the answer to the original question is that in OSPF hop count is unlimited. The delivery of data packets may be bounded by TTL but advertisement of destinations in OSPF is not limited at all by hop count.