#! perl -slw
use strict;
use Data::Dump qw[ pp ];

my( %data, %subhash, $last );
while( <DATA> ) {
    if( /^H/ ) {
        if( $last ) {
            $data{ $last } = { %subhash };
           undef %subhash;
       }
        ( $last, my( $key, $val ) ) = m[(\S+)\s+(.+)\s+(\S+)$];
        $subhash{ $key } = $val;
    }
    else {
        my( $key, $val ) = m[^\s+(.+)\s+(\S+)$];
        $subhash{ $key } = $val;
    }
}
$data{ $last } = { %subhash };

pp \%data;

__DATA__
Hostname1     1.1.1.1     Cisco
              Chassis Serial Number xyz123
              Interface Gig0/0/31
Hostname2     2.2.2.2     Juniper
              Chassis Serial Number abc123
              Interface Gi-0/0/31