Some protocols can in-line signal a port jump and/or create connections one or both ways "at will". UDP and TCP are special because they have 65536 possible src and dst ports that can help connection tracking.
Here are examples of protocols that has that problem:Įven if the traffic is unencrypted it can not be deduced where to NAT a response outside packet, if more than one inside client uses the same protocol to the same outside ip address. When a response outside packet later arrives at the NAT device (firewall), it can not deduce which client to send it to. C1, C2) connect to the same outside server ip address (S) and the traffic is not tcp and udp. NAT - Network address Translationĭue to IPv4 address shortage, the internet society began to use NAT, and therefore the firewall also need to be NAT aware.Ī real problem with NAT is when more than one inside clients (e.g. number of connections attempt - "SYN"-attacks, packet storms.number of connections per (src/dst) ip address.A statefull firewall can additionally moderate trackable traffic by: The better ip firewall - a statefull firewall - can pass packet by packet - and if possible (e.g. Routers:Netgear R7000, R6400v1, R6400v2, EA6900 (XvortexCFE), E2000, E1200v1, WRT54GS v1.The simplest ip firewall - a packet filter firewall - can pass packet by packet or drop them based on: Yes it can be disabled, (I actually think it does not work at all in bridging mode) Perfect stealth means that router does not answer ping and the GRC scanner finds no evidence that a computer/router would exist at that IP.Ĭan SPI Firewall be disabled if I'm just running the router in Repeater Bridge Mode and the primary router has a firewall, or does it still provide some benefit? It says the ports are closed if it is still able to see them, and they are stealth if it finds no evidence of the existence such port. GRC Shields Up marks them in red and says they're open ports. You mean non-stealth ports? As the ports would still be closed due to NAT. I don't say they solve everything, but open ports are invitations to hammering and further attacks. Of course, torrents and servers will reveal your IP, as ordinary web surfing also does (to the websites you access). GRC Shields Up gives a perfect stealth status when it has no portscan evidence that behind your IP would exist anything like a computer or router. It gives you a "perfect stealth" rating with GRC Shields Up, Kernel panic: Aiee, killing interrupt handler! Sounds like a reply from someone who hasn't understood. It greatly improves computer security, seen that your devices are always behind at least one firewall.Ģ times RT-AC56U running DD-WRT 45493 (one as Gateway, the other as AP, both bridged with LAN cable)Į4200 V1 running freshtomato 2020.8 (bridged with LAN cable)ģ times Linksys WRT610N V2 converted to E3000 and 1 original E3000 running freshtomato 2020.8 (bridged with LAN cable) It gives you a "perfect stealth" rating with GRC Shields Up, unless you forward ports or otherwise open them (e.g. Thats, what the SPI firewall in DD-WRT does and other softwares. Such a firewall will pass all outgoing packets through but will only allow incoming packets if they are part of an ESTABLISHED connection, ensuring that hackers cannot start unsolicited connections with the protected machine. The client will then respond with a packet in which only the ACK bit is set, and the connection will enter the ESTABLISHED state. If the service which the client has requested is available on the server, the service will reply to the SYN packet with a packet in which both the SYN and the ACK bit are set. All packets with the SYN bit set are considered by the firewall as NEW connections.
When a client initiates a new connection, it sends a packet with the SYN bit set in the packet header. The stateful firewall depends on the three-way handshake of the TCP protocol when the protocol being used is TCP when the protocol is UDP, the stateful firewall does not depend on anything related to TCP. There is the shortcut described, but the function, too! Especially considering NAT itself provides some 'protection'. I'm asking what, exactly, it does in DD WRT. TL-WR841ND BS-build 23919 Client Bridge ( Routed )
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