$ echo '# Host 1
host 45583 {
filename "junk1.cm";
hardware ethernet 11:42:a3:d4:55:83;
fixed-address 10.100.34.114;
}
# Host 2
host D78C3 {
filename "junk5.cm";
fixed-address 10.100.34.117;
hardware ethernet 11:42:a3:FD:78:C3;
}
# Host 3
host 3A684 {
filename "junk6.cm";
fixed-address 10.100.34.119;
hardware ethernet 11:42:a3:13:a6:84;
}
# Host 4
host 46d54 {
filename "junk4.cm";
fixed-address 10.100.34.120;
hardware ethernet 23:10:3d:14:6d:54;
}
' | perl -e'
$/ = "}\n";
while ( <> ) {
    s/(fixed-address.*\n)(hardware ethernet.*\n)/$2$1/;
    print;
    }
'
# Host 1
host 45583 {
filename "junk1.cm";
hardware ethernet 11:42:a3:d4:55:83;
fixed-address 10.100.34.114;
}
# Host 2
host D78C3 {
filename "junk5.cm";
hardware ethernet 11:42:a3:FD:78:C3;
fixed-address 10.100.34.117;
}
# Host 3
host 3A684 {
filename "junk6.cm";
hardware ethernet 11:42:a3:13:a6:84;
fixed-address 10.100.34.119;
}
# Host 4
host 46d54 {
filename "junk4.cm";
hardware ethernet 23:10:3d:14:6d:54;
fixed-address 10.100.34.120;
}