27 votes

How does the airconditioner app on my phone access my aircon controller through my router?

Many smart home devices make their own outgoing connection to a server run by the vendor, and the vendor's smartphone app also logs into your account on the vendor's server, and the server takes care ...
Spiff's user avatar
  • 104k
10 votes

How does the airconditioner app on my phone access my aircon controller through my router?

Without going into technical detail - which a) I'm not very good at & b) is likely to be different depending on app & IOT device… Both connect to a 'central server' out there on the interwebz, ...
Tetsujin's user avatar
  • 49.5k
7 votes
Accepted

Why does peer-discovery work for IPv6 but not IPv4?

And the peer-discovery functionality that I've built works by simply sharing the IP address of connected nodes along with their announced port for incoming connections. There are a few issues with ...
u1686_grawity's user avatar
5 votes
Accepted

iptables nat table does not work as expected?

iptables NAT is stateful and per-flow rather than per-packet. Only the first packet of a flow (that is, packets belonging to an unknown flow) is sent through the 'nat' table – all subsequent packets ...
u1686_grawity's user avatar
4 votes
Accepted

How routers deal with only one external IP?

The following is a very basic explanation. Your devices uses private addresses. Private addresses are subnets/networks with the following IP addresses (see RFC 1918): 10.0.0.0 to 10.255.255.255 172....
Reddy Lutonadio's user avatar
4 votes
Accepted

How to configure VirtualBox NAT network with IPv6?

While it might be in theory possible for VirtualBox's NAT implementation to forward IPv6 connections to an IPv4 host, such protocol translation tends to introduce a lot of complications, such as "...
u1686_grawity's user avatar
4 votes

How does remote users connect to a device on a local network behind NAT without port forwarding or VPN?

In most cases, the internal device behind the NAT initiate the connection to a remote server on the internet. Then the person who need to administrate the device connect to this server and use the ...
S. Brottes's user avatar
  • 1,177
3 votes

Is there any way to setup 3 routers same network without double NAT?

Yes. Disable the NAT and DHCP Server features of routers 2 & 3 so that they act as transparent bridges, not routers. If either of those two extra routers don't have a way to turn off NAT and make ...
Spiff's user avatar
  • 104k
3 votes

How routers deal with only one external IP?

From googling I understand that all routers do is performing NAT NAT is still an "add-on" feature on top of actual routing. When a reply comes in, after NAT it still follows the regular ...
u1686_grawity's user avatar
2 votes

Hyper-V: NAT not functioning / guest cannot access internet

You may want to check how your NAT is using ExternalAddresses. It can be done with following powershell command: Get-NetNatExternalAddress On my system I noticed the first entries were actually local ...
pawrog's user avatar
  • 41
2 votes
Accepted

How to enable hairpin NAT between docker containers using bridge network

Is there a way to access Container B from Container A without changing the host configuration or knowing Container A's dynamic IP? The easiest and the recommended way is to create a user-defined ...
Sathyajith Bhat's user avatar
  • 61.8k
2 votes
Accepted

what is the most stable and fastest tunnel for a VPN?

To answer your headline question (but this does not help you) - Wireguard is probably the most stable and fastest tunnel for a VPN. It is designed to be small and lightweight, and is the most ...
davidgo's user avatar
  • 70.6k
2 votes

Provide access to the Internet via NAT on the one router from the network separated by another router

According to mr. @u1686_grawity's recommendations in the comments, I've checked with tcpdump all the interfaces in my network topology and it appeared that there were no route to 192.168.57.0/27 on ...
Ivan's user avatar
  • 21
2 votes

Connect multiple devices behind single LAN IP Address

Yes, that's exactly what NAT is for. Yes, you could use a dedicated router, even the cheapest consumer home gateway router, to do this. Yes, you could use Windows' built-in Internet Connection Sharing ...
Spiff's user avatar
  • 104k
2 votes

Best way to access my computer/network from anywhere while having public IP. ISP uses NAT

A static or dynamic ip-address doesn't matter. The problem is NAT. This prevents connections from the Internet from reaching your router. Essentially a NAT makes the connection one-way. From your ...
Tonny's user avatar
  • 31.4k
1 vote

How can I simulate NAT reflection failure with `iptables`?

Add an ordinary 'DROP' rule that blocks 'INPUT' packets from your router's IP address to this port. Due to the way hairpinning "solves" the underlying problem, all hairpinned connections ...
u1686_grawity's user avatar
1 vote

Creating an IP alias for a device on another subnet behind a VPN

For an address to "exist" in a subnet, something must answer ARP queries for it. If you want the router to handle the address, then the router must answer ARP.1 So that means either a) the ...
u1686_grawity's user avatar
1 vote
Accepted

In Linux how to loop-back the internal traffic that's destined to the server's own NATed public IP?

Add identical NAT rules to the server's own firewall. You need to place them in the 'OUTPUT' chain instead of the usual 'PREROUTING' (however, still in the 'nat' table). For example, in nftables: ...
u1686_grawity's user avatar
1 vote

Can't ping my external CGNAT IP address from external network

"Your" CGNAT IP address is not really yours; it belongs to the NAT gateway. Depending on the ISP's setup, it might not always be pingable: The ISP might have simply blocked ping requests on ...
u1686_grawity's user avatar
1 vote
Accepted

Trying to understand how WSL2 networking and routing works when pinging google.com, confused

It works the same way as in your home router. With the default vSwitch configuration that WSL2 creates, your host OS practically becomes a router with a stateful NAT feature – NAT because it also ...
u1686_grawity's user avatar
1 vote
Accepted

Dynamic vs Static NAT? How to tell which and when one or the other is in use?

To directly answer your question as asked, a standard consumer grade internet access router provides staticly-mapped , asymetric, source NAT, when it is allowing its LAN hosts to share a single public ...
Frank Thomas's user avatar
  • 36.1k
1 vote
Accepted

Is using WireGuard keep-alive feature going to create issues when connected for long time?

They certainly can detect it (NAT state tables could easily have a timestamp and often do), but they probably won't bother unless you're using much more than just one port... or unless they're ...
u1686_grawity's user avatar
1 vote
Accepted

How iptables SNAT deal with src port dilemma between port translation fr local ip and DNAT rule that forwards all traffic to the same local ip?

Existing conntrack states (the "NAPT records") always have priority over any -t nat rules. If you remember, the -t nat table is only visited by one packet per connection – that's because any ...
u1686_grawity's user avatar
1 vote
Accepted

Device that uses NAT internally - how to avoid conflicting with connection to internet?

RFC 1918 defines the IPv4 address ranges reserved for private use, such as behind a NAT. It defines the following three ranges: 10.0.0.0/8: 10.0.0.0–10.255.255.255 172.16.0.0/12: 172.16.0.0–172.31....
Spiff's user avatar
  • 104k
1 vote
Accepted

VirtualBox DHCP Server on Nat Network

Not possible - paradox of the chicken and the egg. The host needs to get its IP address when it boots, which is before starting VirtualBox and booting the VM. Having two DHCP servers on the same local ...
harrymc's user avatar
  • 479k
1 vote

NAT masquerade refuses to work on Link-Local network

I found a way to work around this issue when using Network Manager. The link scope is unfortunately hardcoded in Network Manager on the following line of code which automatically selects the scope ...
Kenji's user avatar
  • 113
1 vote
Accepted

NAT not working properly with more LANs - source address is replaced with LAN gateway IP

while NAT is supposed to keep it unchanged but it seems that RouterOS actually doesn't keep up with that rule. It seems that RouterOS does exactly what your NAT rules specify. What you have in your ...
u1686_grawity's user avatar
1 vote

Is it possible to enable UPnP without going into Router web interface?

If you need to change the settings of the modem to add port forwarding (or a DMZ, etc.) you will need to access the modem's control panel. If you look at the information package you received when you ...
Blindspots's user avatar
  • 2,842
1 vote

IPv6 masquerading on linux

This is likely due to the IPv6 masquerading feature being disabled in your kernel. It is a build-time feature switch: https://www.kernelconfig.io/config_nf_nat_masquerade_ipv6?q=&kernelversion=5....
Christoph Sarnowski's user avatar
1 vote

No internet connection in Virtual Machine on selecting NAT in VMWare workstation

I had this problem, after upgrading to V 17.5. None of the previous answers worked. I tried restarting the VMware NAT and DHCP Services. I tried deleting the NAT adapter and creating a new one in the ...
TheColonel26's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible