Refer to the exhibit. Packets received by the router from BGP enter via a serial interface at 209.165.201.1. Each route is present within the routing table. Which interface is used to forward traffic with a destination IP of 10.1.1.19?
Refer to the exhibit. Packets received by the router from BGP enter via a serial interface at 209.165.201.1. Each route is present within the routing table. Which interface is used to forward traffic with a destination IP of 10.1.1.19?
To find the correct interface for forwarding traffic with a destination IP of 10.1.1.19, determine which route in the routing table has the longest prefix length that matches the destination IP. The destination IP 10.1.1.19 matches the route 10.1.1.16/28, because 10.1.1.16/28 covers the range 10.1.1.16 to 10.1.1.31. Other routes have shorter prefix lengths and thus less specificity. Therefore, the packet should be forwarded via interface F0/0.
this if for "forwarding traffic" so longest prefix or more specific route
ip routing questions some times confuse me. Not sure when we need to check AD and when longest prefix. I always choose AD / longest prefix . Need to know whether I should choose AD or prefix
Correct Answer: A
could you explain how to solve this question in detail please?
longest prefix
When multiple routes are present that match the destination address, always check for the "more-specific" route first. The smallest subnet (or highest/longest prefix) would be chosen.
To qualify, the option must match two requirements: 1. It must be in range of the advertised route. 2. If there are multiple legitimate routes, it is the route with the longest match. Is test 1 satisfied?... 10.1.1.16/28 has (32-28 = 4-bits for host addresses). 2^4 = 16 hosts (well, excluding N/W and B/C addresses we get 14 usable hosts). Range is 10.1.1.16 -> 10.1.1.31, and 10.1.1.19 falls within this range. Is test 2 satisfied? This route is a /28, which is longer than any other. If there were multiple /28 routes, then choose the one with the lowest AD value (in this case, EIGRP then OPSF, then RIP).