Exam 200-301 topic 1 question 342 discussion

I saw a bunch, bunch, bunch of these on the CCNA. They were all pretty easy. Find the network that the IP fits in, look at the prefix length, if you have 1 that is longer than the rest chhose that as answer. If there is more than 1 with the same longest prefix move over to AD and pick the lowest value. Once again if duplicate lowest move over to metric. Watch for the tricky non-default AD and DO NOT pick by code letter because they change ADs on some of them.

A is right Routing preference *Longest Prefix *AD *Metric

Answer A

A is correct

Since the 3 networks have different masks, the Router understands they are different networks and installs the 3 routes. So, the longest prefix will be decided. Ref: https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/8651-21.html

A - Longest prefix

Guys, how can I post a question on this website?

The correct answer is A. In computer networking, the longest prefix match is used for IP routing in cases where there are multiple routes to a destination network, and these routes have different network prefix lengths (subnet masks). This method is used regardless of administrative distance and is a fundamental principle of how routers make forwarding decisions in IP networks.

A - Longest prefix

The route characteristic used by the router to forward the packet for the destination IP 172.16.32.1 is: B. administrative distance Explanation: From the output of the "show ip route" command, we can see that there are three different routes for the destination IP 172.16.32.1 with different routing protocols and administrative distances: D 172.16.32.0/27[90/2888597172] via 20.1.1.1 (EIGRP) O 172.16.32.0/19[110/292094] via 20.1.1.10 (OSPF) R 172.16.32.0/24[120/2] via 20.1.1.3 (RIP) The administrative distance is a measure of the trustworthiness of the source of the routing information. The lower the administrative distance, the more trustworthy the source. When there are multiple routes to the same destination, the router will choose the one with the lowest administrative distance. In this case, the route with the lowest administrative distance is the RIP route, which has an administrative distance of 120. Therefore, the router will use this route to forward packets to the destination IP 172.16.32.1.

When a router is running multiple routing protocols and has multiple routes to the same destination network, it will use the administrative distance to determine which route to use. The administrative distance is a value assigned to each routing protocol, which indicates the trustworthiness of the routing information provided by that protocol. In general, the router will prefer the route with the lowest administrative distance, regardless of the prefix length or any other factors. If there are multiple routes with the same administrative distance, the router will then use the longest prefix match to determine the best route. ???

A router uses longest prefix match when it has multiple routes to a destination with different prefix lengths. The router prefers the most specific prefix that matches the destination IP address bit-by-bit regardless of the cost or metric associated with each route.

A is correct

/27 is the Highest prefix inclusive of the destination IP address therefore the router uses that route based on the Longest Prefix First rule.

In the given question all routes have same prefix so it would use AD .Therefore ,it should B.

Surely A. Answers B, C and D plays ahead in building the routing table while choice A (longest prefix match) plays later in selecting which route for a host that fits in the many target subnets in the routing table. Remember first that the routing table shall have only one route to any one subnet (except for load balancing cases which needs more detail I like to skip here). Two subnets are not the same subnet if they differ in either subnet ID and/or Subnet mask. Answer B, Administrative distance plays first to select which route to be inserted when we have 2 routes learned by the router using 2 different routing protocols. In this case the route with the lowest AD will be inserted. Answer C (Cost for ospf) and answer D (metric in general) are used (lowest value) to select between 2 routes learned using the same protocol) In the question, we have 3 routes to 3 different subnets, but if the host belongs to more then one (all of them in this case), we select the more specific subnet (the one with the longest match as our route)

typo - longest prefix