If there are two routes to the same destination then the largest prefix/mask is used to make a choice. Prefix length trumps all other route attributes. A video about longest match routing and how it can steer routes the correct and incorrect path. Longest prefix match (also called Maximum prefix length match) refers to an algorithm used by routers in Internet Protocol (IP) networking to select an entry from a forwarding table.. Because each entry in a forwarding table may specify a sub-network, one destination address may match more than one forwarding table entry. PC needs AND operati (and Bitwise XOR is used to figure out wildcard operations). 1) Longest prefix match. To make it more clear lets lab it up. All intelligent networking devices use both Bitwise AND operations used to figure out subnetting. it is the way of an IP Router to select which route it will choose to forward the packets to. The longest prefix match can come up particularly when you have summary routes. Longest Prefix Match: Understanding Advanced Concepts in VPC Peering VPC Peering Basics. First, what is Longest-Prefix Match? Longest Prefix Match. The example below has the same topology with our previous example but with an additional router, R5. So, the answer in your case would be A and C. Correct Answer: C. Explanation: The destination IP address 10.1.5.65 belongs to 10.1.5.64/28, 10.1.5.64/29 & 10.1.5.64/27 subnets but the “longest prefix match” algorithm will choose the most specific subnet mask; the prefix “/29″ will be chosen to route the packet. If there is a tie, the AD(administrative distance) is used to determine the choice. The less the AD, the more believable/preferable the route is. Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube. On CUBE and SIP gateway when one voice dial peer has only one destination pattern, this introduces dial peer configuration in large amounts when multiple destination patterns are used. It compares the Destination IP Address of the packet it receives to each entry it has in its routing table, the longest network bits that has a match wins. 1) Area Types [Intra, Inter, External E1, External E2, NSSA N1, NSSA N2] 2) Longest prefix match Prefix Length - The longest-matching route is preferred first. The link from R1 to R5 is on the 10.0.3.0/24 network and it is directly connected. 2) Lower Administrative Distance [In case of different routing protocol] 3) Lower Metric [In case of same routing protocol] Note: There will be an extra tie-breaker for OSPF alone. In AWS, a Virtual Private Cloud (VPC) peering connection is a networking connection between two VPCs which allows you to route specific traffic between them using either private IPv4 addresses or IPv6 addresses. 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