As a final example, consider the following networks:
192.168.1.0/25
192.168.1.128/25
192.168.2.0/24
192.168.3.0/24
192.168.4.0/26
192.168.4.64/26
192.168.4.128/26
192.168.4.192/26
Try to figure out the summary address that can be used for these networks. If you look carefully the third octet forms a contiguous block of 4 and can be summarized with the address 192.168.1.0 255.255.252.0 or 192.168.1.0/22.
In the last example notice that we summarized a contiguous block of class C using a mask. This is called supernetting. Supernetting is an extension of VLSM and summarization. In summarization you summarize networks subnetted while in supernetting you summarize a block of contiguous blocks of Class A, B or C networks. Supernetting is usually practiced by ISPs to reduce the Internet routing table size.