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=