The Routing Table - Cisco Academy

Once again, Figure 16 shows us that none of the child routes have 24 left-most bits (/24 mask displayedin the parent route) that match the destination IP address of 172.16.4.10.Figure 16IP Packet 172.16.4.10 10101100 00010000 00000100 00001010No match!Child Route 172.16.3.0 10101100 00010000 00000011 00000000Child Route 172.16.1.0 10101100 00010000 00000001 00000000Child Route 172.16.2.0 10101100 00010000 00000010 00000000Now, what happens next?Because the default is now, ip classless, the routing process continues searching the routing table,beyond this parent route and its child routes. The routing process will search the routing table for a routewith a subnet mask fewer than the 16 bits of the previous parent route. In other words, the router will nowcontinue to search the other routes in the routing table where there may be fewer bits that match, but stilla match.The 192.168.1.0/24 route does not match have 24 left-most bits that match with our destination IPaddress. How about the default route? How many bits need to match?S* 0.0.0.0/0 is directly connected, Serial1The mask is /0 so zero or no bits need to match. A default route, if used in the search, will be the lowestbit-match.If no other route matches, the default route will! (Figure 17)Figure 17Routing Behavior: classless (ip classless)Packet’s Destination IP Address: 172.16.4.10RouterB#show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP,Gateway of last resort is 0.0.0.0 to network 0.0.0.01. Match 172.16.0.0/24 is subnetted, 3 subnets2. No Match R 172.16.1.0 [120/1] via 172.16.2.1, 00:00:13, Serial03. No Match C 172.16.2.0 is directly connected, Serial04. No Match C 172.16.3.0 is directly connected, FastEthernet0C 192.168.1.0/24 is directly connected, Serial15. Match! S* 0.0.0.0/0 is directly connected, Serial1RouterB#14