The synopsis of 'known_hosts' file is as follows:
SYNOPSIS: hostname key-type host-public-key # comment ! negate EXAMPLE: 192.168.1.2 ssh-rsa AAAAB3NzaC1...nXIDE= 192.168.1.2 ssh-dss AAAAB3NzaC1...nXIDE= 192.168.1.2 1024 35 13032138...794461 #192.168.1.3 ssh-rsa AAAAB3NzaC1...nXIDE= 192.168.1.2 1024 35 13032138...794461 *.example.com,!mail.example.com ssh-rsa AAAAB3NzaC1...nXIDE=