A meta REJECT
rejeita o pacote. Se você não especificar com qual mensagem ICMP rejeitar, o servidor por padrão enviará de volta a porta ICMP inacessível (tipo 3, código 3).
--reject-with
modifica esse comportamento para enviar uma mensagem ICMP específica de volta ao host de origem. Você pode encontrar informações sobre --reject-with
e as mensagens de rejeição disponíveis em man iptables
:
REJECT
This is used to send back an error packet in response to the matched packet: otherwise it is equivalent to DROP so it is a terminating TARGET, ending rule traversal. This target is only valid in the INPUT, FORWARD and OUTPUT chains, and user-defined chains which are only called from those chains. The following option controls the nature of the error packet returned:
--reject-with type
The type given can be:
- icmp-net-unreachable
- icmp-host-unreachable
- icmp-port-unreachable
- icmp-proto-unreachable
- icmp-net-prohibited
- icmp-host-prohibited or
- icmp-admin-prohibited (*)
which return the appropriate ICMP error message (port-unreachable is the default). The option tcp-reset can be used on rules which only match the TCP protocol: this causes a TCP RST packet to be sent back. This is mainly useful for blocking ident (113/tcp) probes which frequently occur when sending mail to broken mail hosts (which won't accept your mail otherwise).
(*) Using icmp-admin-prohibited with kernels that do not support it will result in a plain DROP instead of REJECT