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Questão que envolve o conhecimento de portas :
NTP - 123
DNS - 53
SSH - 22
HTTP - 80
SNMP - utiliza duas portas: 161 - Agente, o servidor 162 - Gerente - o cliente
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Rodrigo, acredito que as portas corretas para o SNMP sejam 161 e 162. Confirme para mim, por favor.
As demais estão corretas.
Vamos na fé.
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iptables -I FORWARD -d 10.0.0.1 -p udp --dport 53 -j DROP
DNS - 53 (UDP)
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Esqueminha que montei das principais portas:
portas mais utilizadas:
20 - FTP (Conexão de dados)
21 - FTP (Conexão de controle - full duplex)
22 - SSH - (SFTP)
23 - Telnet;
25 - SMTP;
53 - DNS (UDP e TCP)
69 - TFTP (UDP)
80 - HTTP;
110 - POP3;
123 - NTP
143 - IMAP;
443 - HTTPS.
990 - FTPS
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O protocolo que corresponde à porta 53 é o DNS.
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d-
Iptables and ip6tables are used to set up, maintain, and inspect the tables of IPv4 and IPv6 packet filter rules in the Linux kernel. Several different tables may be defined. Each table contains a number of built-in chains and may also contain user-defined chains.
https://man7.org/linux/man-pages/man8/iptables.8.html
DNS uses Port 53 which is nearly always open on systems, firewalls, and clients to transmit DNS queries. Rather than the more familiar Transmission Control Protocol (TCP) these queries use User Datagram Protocol (UDP) because of its low-latency, bandwidth and resource usage compared TCP-equivalent queries.
https://unit42.paloaltonetworks.com/dns-tunneling-how-dns-can-be-abused-by-malicious-actors/