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What's the default Administrative Distance of BGP (external routes [eBGP])? 20 Whats the default Administrative Distance of IS-IS? 115 What's the defaul Administrative Distance of EIGRP (external routes)? 170 What's efault Administrative Distance of IGRP 100 What's the default Administrative Distance of BGP ( internal routes [iBGP])? 200 What's the default Administrative Distance of DHCP default route? 254 What's the default Administrative Distance for connected interfaces? 0
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What's the default Administrative Distance for Static route? 1 What does the show ip route command lists? It lists each route's administrative distance as the first of the two numbers inside the brackets. The second number in brackets is the metric. Whats the IP protocol type of a Hello message? Type 89 What are LSUs? the the OSPF messages that actually send the LSAS between neighbors are called Link- State Update (LSU) packets. That is, the LSU packet holds data structures called link-state advertisements (LSA). The LSAS are not packets, but rather data structures that sit inside the LSDB and describe the topology. What is rhe definition of neighbor routers? All OSPF routers on the same link that reach the 2-way state that is, they send Hello messages and the parameters match are called neighbors. What are adjacent neighbor routers? All OSPF routers on the same link that reach the 2-way state that is, they send Hello messages and the parameters match are called neighbors. The subset of neighbors for
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What's the best practice of configuration of the reference-bandwidth to allow for future upgrades with higher bandwidth? Use a reference bandwidth of a faster speed than the fastest interface in the network, to allow room for higher speeds. For instance, in that same enterprise, whose fastest link is 10 Gbps, set the reference bandwidth to 40 Gbps or even 100 Gbps to be ready for future upgrades to use 40-Gbps links, or even 100-Gbps links. (For example, use the auto-cost reference-bandwidth 100000 command, meaning 100,000 Mbps or 100 Gbps.) That causes 100 - Gbps links to have an OSPF cost of 1, 40-Gbps links to have a cost of 4, 10-Gbps links to have a cost of 10, and 1-Gbps links to have a cost of 100. Conf t Int g0/0/ ip ospf network point-to-point no ip ospf network (broadcast) Conf t ip ospf 1 shutdown Which statements are correct about OSPF? A. OSPF can use hierarchical routing to reduce router load. B. OSPFV2 supports both IPV4 and IPV6 routes. C. OSPFV3 does not support IPV4 routes. D. OSPF performs automatic route summarization.
- Answers A and C are correct. OSPFV2 and v3 can be configured as multi-area to reduce router load. Answer B is wrong; OSPFV2 supports only IPV4 routing, just as OSPFV supports only IPV6 routing. Answer D is wrong because OSPF supports only manual summarization.
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How is the OSPF router ID determined? Choose all that apply. A. The highest IP address on any physical or virtual interface at the moment of OSPF startup B. The first interface to be activated for OSPF on the router C. The lowest IP address on any physical or virtual interface at the moment of OSPF startup D. The last interface to be activated for OSPF on the router E. Manually using the router-id command Answers A and E are correct. The physical interface with the highest IP will be chosen as the router ID- unless there is a loopback interface, in which case the highest IP on any loopback will be chosen- unless the router-id command is used, in which case the specified IP will be used as the router ID. Who developed OSPF? When? The Open Shortest Path First (OSPF) protocol was developed by the Internet Engineering Task Force (IETF) in 1988 as a more scalable solution than RIP. What are the characteristics of OSPF? OSPF is an open standard Is not Cisco proprietary It uses the Shortest Path First (SPF) algorithm developed by Edgar Dijkstra. It is a link-state routing protocol, which means that it sends updates only when there is a change in the network instead of sending routing updates, it sends LSA instead How does OSPF work?
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Router (config-router)#auto-cost reference-bandwidth 1000 How does OSPF routes packets to their destination? The SPF algorithm places each router as the root of a tree and calculates the shortest path from itself to each destination. shortest path then gets put into the routing table and is used to route packets to their destination. What's hierarchical Routing? An important concept to grasp with OSPF is that it is a hierarchical protocol. Hierarchical routing protocols break up your autonomous system into multiple areas and summarize routes between areas. If summarized wisely, you can cut down a significant portion of routing updates by advertising only the summarized route. What are the benefits of route summarization? •Less processing on routers: Fe wer networks to advertise and store in the database, less calculations for route changes. •Instability hidden from other routers: If a single network goes down in area 2, it will not affect the routers in area 0 and area 1. •Fast convergence: Because fewer routes are sent to area 0, the routers in areas 0 and 1 can converge faster. •Less bandwidth overhead: There is less bandwidth because only one route is sent, so the advertisement is smaller. •Greater control over routing updates: Because you gain control over routing updates, you can control what routes get sent from one area to another. Whats the main area in OSPF?
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You might have noticed that both area 2 and area 1 are connected via area 0. Area 0 is the BACKBONE AREA in OSPF, and all other areas must be connected to it. Routes are then summarized into your backbone area, and from the backbone into other areas. When is a designated router is elected? FThe designated router (DR) is elected on only two types of networks: •Broadcast multiaccess: Ethernet, Token Ring •Nonbroadcast multiaccess: Frame Relay, ATM, X. How DR and BDR are elected? 1 .The router with the highest priority becomes the DR.The router with the second highest priority becomes the BDR. Priority is a number between 0 and 255 and is configured on an interface with the command ip ospf priority priority_number. The default priority is 1, and if the router is set to priority 0, it will never become a DR or BDR.
- In the case of a tie, such as when every router's priority is left to the default of 1, the tiebreaker is the router with the highest router ID. Whats a router ID? Every router has an identifier called a router ID (RID) that's used to identify itself in its messages. The router ID is an IP address and is assigned as follows: •The router ID can be configured with the router - id command under the OSPF routing process. You can choose a valid IP address that you are using on the router or make up a new one. •If the router - id command is not used, the numerically highest IP address on any loopback interface is chosen as the router ID. •If you do not have any loopback interface s configured, the highest IP address on any active physical interface is chosen as the router ID.
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Routerl (config)#router ospf 100 Routerl (config-router)#network 192.168.1.1 0.0.0.0 area 0 Routerl (config-router) #network 192.168.50.1 0.0.0.0 area 0 Suppose a router has the following IP addresses on its various interfaces: 172.16.0. 172.16.0. 172.16.0. 172.16.0. 172.16.0. How to configure OSFP to accept all interfaces putting them all in area 0 except the one with the address 172.16.0.13 using only one network statement? Network 172.16.0.16 0.0.0.15 area 0 13 = 00001101 17 = 00010001 21 = 00010101 25= 00011001 29= 00011101 Match first 4 bits and set wildcard mask to 0's and the remaining bits to 1's of only the adresses that you want to allow ( excluding 172.16.0.13) = 00001111 Now the whole addresss= 00000000.00000000.00000000. How to configure the OSPF priority? Conf t Int g0/0/
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ip ospf priority 100 How to configure the OSPF cost? Conf t Int g0/0/ Ip ospf cost 100 How to configure a single interface as passive? Conf t Router ospf 100 passive-interface g0/0/ How to configure a router with all interfaces as passive? router ospf 100 passive-interface default What are the differences between OSPFv2 and OSPFv3? •OSPFV2 does not support IPV6 routes and OSPFV3 does not support IPV4 routes. Therefore, if you have a dual-stack router (one which uses both IPV4 and IPV addressing), you must run both versions of OSPF. •The characteristics and behavior of OSPFV3 are the same as for OSPFV2. There are some differences in the details of the LSA structure, but that level of detail (the actual guts of the LSA) is well beyond the scope of CCNA.
