Finding the matching route on a router - please help

why cant 172.16.4.3 fit in the 172.16.0.0/22 :

instead of 172.16.0.0/16

Because 172.16.4.3/22 has the network address 172.16.4.0. But route 172.16.0.0/22 has the network address 172.16.0.0.

The rule is: The route is a match only when the network addresses of both the route and the packet are exactly the same using the subnet mask provided by the route.

If more than two routes match, you choose the most specific route. (i.e the one with the highest subnet mask).

Hope this helps and doesn't confuse.

yes /22 is the same as 255.255.252.0 which means the subnet go up by the power of 4.
so the subnets will be
0
4
8
12
16
20
24


why cant 172.16.4.3 fit in the 172.16.0.0/22

instead of 172.16.0.0/16

You've answered your own question .

172.16.0.0/22 = 172.16.0.0 - 172.16.3.255