Route summarisation: one route for many subnets

The idea

hqLaptop at headquarters reaches a branch's staff, guest and printer subnets through two routers, coreRouter and branchRouter. One route can stand for all of them, if what it covers but does not have is dropped.

Steps

1. A route for every subnet

   Every route is a line that each router must store and search, so their number matters. The branch's networks are cut from 10.0.4.0/24 (VLSM); coreRouter reaches them through branchRouter, 10.0.4.243.

   coreRouter:~# ip route

2. One summary route

   The three share their first 24 bits, 10.0.4, and their next hop, so one route for that block can stand for all. Add it; the lab then removes the three.

   coreRouter:~# ip route add 10.0.4.0/24 via 10.0.4.243
   coreRouter:~# ip route
   hqLaptop:~# ping -c1 -W1 10.0.4.106