Questions tagged [nat]

For questions about Network Address Translation (NAT), a method of modifying network address information in IPv4 packet headers.

Filter by
Sorted by
Tagged with
65
votes
7answers
19k views

Why are IPv4 addresses running out?

I understand that we are running out (or ran out already?) of IPv4 addresses, but I don't really understand why that is. Right now, every home has its own IPv4 address (dynamically assigned, but still,...
7
votes
2answers
2k views

NAT Overlapping

I am trying to do some networking lab. Basically, I have a network like this: So, is it possible to configure NAT router in such way, that PC1 and PC2 can access remote HOST and each other. The ...
12
votes
2answers
6k views

How does the router know how to route the packets to my terminal?

Suppose I have a network of 2 computers, each having a private network address of 192.168.1.101 and 192.106.1.102. For my public ip address, it is 10.2.10.172. When I make a http request to google....
12
votes
2answers
4k views

How NAT / PortForwarding / TCP/IP works?

I recently read an article entitled how NAT works. Some things still remain unclear to me. I would be thankful if someone could explain. Below is the part of the article regarding DynamicNAT that is ...
10
votes
2answers
3k views

What do these three options in a Cisco Router NAT configuration mean?

In a standard Static PAT configuration, where one IP:Port combination is always mapped to another IP:Port combination, there are three possible combinations of inside/outside/source/destination that ...
8
votes
1answer
2k views

UDP hole punching NAT port

I just read an article about the process of "punching holes" with the UDP protocol. I understand how it's done, but I have one last question to clear up things. We have the rendezvous server and ...
3
votes
1answer
892 views

How does a router know to which PC in a network to send a response from a server?

When my PC sends a request to a server, the transmitted IP address is the one of my private network. When the server responds to the request, how does the router know to which PC in the network to ...
2
votes
3answers
588 views

Why can't a host B act as a server, and accept TCP connections, when sitting behind a NAT?

Originally, I thought I intuitively understood why B can't accept TCP connections, however when I read about how P2P applications circumvent this exact problem by using an intermediate peer that is ...
10
votes
1answer
4k views

How does NAT share one public IPv4 address across multiple private IPv4 addresses [closed]

I think it's a very classical question, but, thought I've have some background, I don't have enough vocabulary anymore to search and understand correctly in the Web. Let's say I have a home network ...
7
votes
3answers
4k views

How does NAT decide which connections are inbound, and which are outbound?

I'm building a P2P application that needs to be able to access nodes behind a NAT. This NAT does not allow inbound connections, therefore the nodes outside the network cannot reach out to the nodes ...
6
votes
5answers
7k views

Why does NAT translate a source port?

I’m beginning to learn about nat and I was wondering why does NAT translate a source port? Doesn’t a port represent an application that’s requesting a service? So why must it be translated? Also what ...
2
votes
1answer
2k views

Connecting on a port on a computer behind NAT

I have a question about NAT, and this question has answered most of it : How NAT / PortForwarding / TCP/IP works? What I am left confused on, is in this part of the question: Why does this work? ...
13
votes
2answers
29k views

Open a range of TCP ports in Cisco IOS NAT

ip nat inside source static 192.168.1.10 10.10.10.9 route-map RANGE ! route-map RANGE permit 100 match ip address 102 ! access-list 102 permit tcp host 192.168.1.10 range 3000 3389 any The ...
6
votes
1answer
3k views

Cisco 867 forward UDP port range

I need to forward an UDP port range to a specific private IP address in my LAN. In order to forward one port to an internal IP I do: access-list <acc_list_number> permit <port_type> any ...
5
votes
2answers
2k views

IPv6 and online privacy and security

I am studying up on IPv6 and part of the talk was about how the machines generate or can have multiple IPv6 addresses for internal use and external use. Does this mean that there is no longer a "...
3
votes
2answers
6k views

How is harpinning (NAT loopback) used in practice?

I have never had to use hairpinning in the past and so far, reading its description on Wikipedia, I don't see many use cases for this technology, apart from some requests from selected users inside ...
2
votes
2answers
836 views

Access internal webserver with domainname points to external IP

We have a webserver on our LAN. Externally, we can use the public domainname (let's say business.com) to access the website. Internally, we need to use the local IP. We also want to use the public ...
9
votes
3answers
3k views

Cisco NAT hairpinning

I have a Cisco router configured NAT (4 static NAT and dynamic NAT). My problem is that I can't access internal servers using public IP addresses from the internal network. I know what the problem ...
9
votes
2answers
8k views

pfSense multi-wan Bridge, NAT, Load balancing and CARP

Context I currently have : 1 pfSense 2.0.2 router (on a Firebox X-Peak X5000) 2 WAN 1 LAN 3 Servers My interfaces WAN1 68.XX.XXX.98 to 69.XX.XXX.102 WAN2 65.XXX.XXX.58 to 66.XXX.XXX.62 LAN 192.168....
8
votes
1answer
1k views

NAT VLANs with same IP Subnets

I have a VMware environment in which VMs are running a simulation suite. The software used has hardcoded IP addresses, about 10-15 VMs, and we are running multiple instances of this software each in ...
6
votes
3answers
2k views

How is NAT a hack?

Forgive me if this sounds a little amateurish, or if this is the wrong stackexchange, but...most of my entirely life I've had ipv4 behind a NAT router. I've been told that this was a hack; simply ...
4
votes
1answer
232 views

How are IPv4 Addresses provided uniquely to domains?

this question has been bothering me for sometime and I've yet to receive a clear answer (it bothers me whenever I go to sleep). I would like to receive expert answers on this matter. Who mainly ...
4
votes
1answer
1k views

CISCO Port Forwarding Going to Wrong Machine

We are running a few services in our internal network that we would like to expose to the outside world. At first we were having trouble with email, dns, and www. Not sure what happened but email and ...
3
votes
2answers
2k views

where to NAT?where to run BGP?

in this diagram : we are peering with 2 ISPs, let's say I have a class c IP space like 200.200.200.0/24 and let's say my ASN is 65000, the thing is where should I run NAT? on which device? I mean on ...
2
votes
1answer
2k views

Port-forwarding rule on Cisco ASA not working - “Drop-reason: (acl-drop) Flow is denied by configured rule”

New to Cisco, so I hope this question isn't too noobish. I am trying to setup a port-forwarding rule to allow "any" SSL traffic in from "Outside" to the web server on my LAN. The problem is apparently ...
21
votes
3answers
4k views

CEF operations on L3 switch vs router

I understand that L3 switches use CEF for faster packet forwarding. However, CEF will not work for packets that need to undergo NAT. Does this mean CEF isn't used by edge routers and edge L3 switches? ...
7
votes
1answer
3k views

Problem with VPN tunel from remote location through ISP (PPTP)

I have network situation like this: ISP Router (modem) - device given to us by our ISP - modem & router in one but it is set into transparent mode - ISP say so ;D we have to find it that it is ...
6
votes
2answers
2k views

PPPoE with NAT configuration broken

We are trying to replace our existing router with a newly purchased Cisco router: GigabitEthernet0/0: PPPoE GigabitEthernet0/1: 192.168.2.1 The PPPoE is getting established perfectly, and I can ping ...
4
votes
3answers
1k views

How does a router a layer 3 device translate port address in PAT, as it is a layer 3 device?

While I was reading about PAT i.e Port Address Translation.The router was configured to translate all the private IP addresses to one single public IP.Since router is a layer-3 device, it can do that ...
4
votes
4answers
724 views

Is there a valid scenario where a router is used to translate a public IP address?

NAT typically refers to router translating an IP address from a private network to a public IP address so that the node on the private network can access public Internet. Is there a valid scenario ...
3
votes
3answers
4k views

IPv6 NAT with Link-Local Address

It's more than usual to find NAT translating IPv4 private addresses (such as 192.168.0.0/16 or 10.0.0.0/8) to non private addresses. Is it possible that NAT translates even IPv6 link-local addresses (...
2
votes
2answers
885 views

Private and Public IPs in the same OSPF area

I will have a routed network with both public and private subnets routed with OSPF. There will be two core routers that both have a default route to the internet. My question is how I make sure that ...
1
vote
1answer
41 views

How to Mitigate DoS by Bindings/Transport Address Exhaustion in NAT64?

Let's say a NAT64 Router only has 1 IPv4 address for bindings, meaning the NAT64 router has a roughly 65535 IPv4 transport addresses. A malicious attacker can then exhaust the entire IPv4 transport ...
1
vote
1answer
122 views

Unsecured devices and IPv6

I'm currently starting to read up on IPv6, and as soon as I heared that every device can/will have a public accessible adreess i got a little freaked out. There are a lot of horror stories about ...