OSPF QUESTIONS & ANSWERS VERIFIED 100% CORRECT!!

ABR's connected over virtual links send all OSPF message types as what to it's neighbor/destination? - The ABR will send its OSPF message types as unicast IP packets to the IP address of the destination router. However, the key take away is that the destination of the virtual link, to form that neighborship, is via the RID of that router noted within the shared Type-1 Router LSA. ABR's create one Type-1 LSA per area. T/F? - T Each router uses it's own what as its LSID? - OSPF enabled routers use their own RID as their LSID. The LSID is a descriptive method of identifying each LSA. How do devices in different areas communicate to one another via an ABR? What does this ABR use? - The ABR generates a Type-3 Summary LSA for each subnet in an area, and advertises each Type-3 LSA into every other area. How does OSPF decide upon its RID? - It's the exact same as EIGRP. It checks to see if you: 1. Manually configured (first) 2. Highest IP address of an up/up Loopback interface 3. The highest IP address of any up/up non-loopback (physical) inteface How many OSPF neighbor states are there? - 8 How many total LSA types are there? - 11If a router needs to flush an LSA from its LSDB, it needs to set the age of that LSA to what? - The router will set the LSA's MaxAge to 3600 seconds (1-hour), and re-flood the LSA. This is in essence its way of poisoning the route. If no OSPF DR and BDR exist, the next step is that each neighbor will want to start exchanging LSDB's. What are the three main steps to this process? - 1. OSPF enabled routers will discover LSA's known to their neighbors but known to thyself. 2. To discover LSA's known by both routers, but the neighbors LSA is more up to date. 3. You will want to ask the neighbor for a copy of all LSA's identified in the first two steps. If the DR and BDR have been elected, no new OSPF neighbor with a higher priority can preemptively take over for the DR/BDR until either or gets shutdown, or fails. T/F? - T If the hello interval is changed on a particular interface, the dead interval is automatically changed to what? - The dead interval will automatically multiply the hello interval by 4x. Therefore, if the hello interval is set to 30 seconds, the dead interval will be changed to 120 seconds. If there are multiple ABR's connected in two area's or greater, filtering should be done on how many routers? - All of them. This is the ideal method unless some path manipulation is being done. If two OSPF enabled routers experience MTU mismatches what state will those routers get stuck on? - EXSTART, and then go down If you have a virtual link(s) formed over a non-backbone area, what is that area's technical name? - This is called the "transit area" and they can not go through a stub area.If you have multiple keys the only authentication method allowed is MD5. T/F? - T If you have multiple keys per interface then the only method of authentication allowed to be configured is Type 2 (MD5). IF you want to prefer one ABR over another to reach a particular destination what two path manipulation techniques would you use? - 1. Summarization 2. Filtering. In the context of path manipulation, what does summarization do? - Summarization on an ABR advertises a less-specific summary route inside an area, so more specific routes are preferred via the other ABR. Let's say you have dozens upon dozens of OSPF enabled routers in a single area. It can become extremely menial and tasking to try and parse through all that data within the `show ip ospf database` command. Therefore, if you want to become more granular in what destination router's LSA you want to look at, what command would you run? - You would issue the `show ip ospf database router x.x.x.x` command. This allows you to filter the OSPF database (LSDB) down to that specific RID. OSPF elects a DR and BDR based on information listed in what? - The hello packet.