Questions tagged [nat]
For questions about Network Address Translation (NAT), a method of modifying network address information in IPv4 packet headers.
630
questions
72
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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,...
- 831
21
votes
3
answers
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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? ...
- 1,005
19
votes
2
answers
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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....
- 301
18
votes
6
answers
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IPv4 Segment 100.64.0.0/10
I recently got to know that IP segment 100.64.0.0/10 has been reserved by IANA for 'Shared Address Space'.
My question is: Can I use the IP Segment 100.64.0.0/10 as a private range in my network (...
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13
votes
4
answers
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What layer of the OSI model does NAT work?
Simple question and the answer is layer 3 of course, but can we say that PAT is working on layer 4 also because it deals with port numbers which is a layer 4 function?
Or is it only a layer 3 ...
- 133
13
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2
answers
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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 ...
- 233
13
votes
2
answers
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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 ...
- 131
11
votes
4
answers
23k
views
Using IP addresses from IP pool given by ISP
My ISP says that it can provide an optic fiber connection with a pool of 4 static IP addresses (subnet 255.255.255.248 i think).
My question is that if I get that connection,
1 ip will be used for ...
- 213
11
votes
2
answers
6k
views
Cisco ASA double NAT with DNS translation
I'm trying to set up double Auto NAT with DNS translation on Cisco ASA 9.0(3), and I'm having a few challenges with the DNS portion. I got double NAT working correctly, such that I have a server in ...
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10
votes
2
answers
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why STUN doesn't work with symmetric NAT?
I read this line from wikipedia.
"STUN does work with three types of NAT: full cone NAT, restricted
cone NAT, and port restricted cone NAT. In the cases of restricted
cone or port restricted ...
- 235
10
votes
3
answers
8k
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interpreting ping results
I'm pinging yahoo.com and am I'm puzzled by the result.
C:\Users\jon>ping -t yahoo.com
Pinging yahoo.com [98.138.253.109] with 32 bytes of data:
Reply from 98.138.253.109: bytes=32 time=195ms TTL=...
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10
votes
3
answers
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Why is symmetric NAT called "symmetric"?
After searching a while, I'm still not able to find a logical explanation on why is it called symmetric NAT.
Where lies the link between symmetric NAT and that each request is mapped to a unique ...
- 203
10
votes
1
answer
4k
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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 ...
- 203
10
votes
2
answers
11k
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How `UDP Hole Punching` Works?
Can anyone explain how UDP hole punching works in a simple way? I know how NAT and PAT works, but can't get a clear idea about UDP hole punching.
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10
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2
answers
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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 ...
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9
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2
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Is there anything stopping me from using Class A addresses on my own network?
I've been reading about IPv4, networking, subnetting and the different classes of addresses.
I understand that IP addresses beginning with numbers from 1 to 126 are considered "Class A" addresses.
...
- 559
9
votes
7
answers
17k
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What is the purpose of subnetting, if we have NAT?
As I know, NAT is the system, that divides IP addresses into two categories - public and private. Public represents the local network from the outside and private represents the device from the inside....
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9
votes
1
answer
3k
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How does NAT Stitching work?
While reading about CISCO NetFlow Analysis I came up with a term named NAT Stitching.
I understand Flow Stitching which join same type of inbound and outbound connection.
But can't find anything ...
- 603
9
votes
2
answers
5k
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How does NAT work with incoming UDP packets from unknown IP
Apologies in advance for the relatively noob question and if this is off topic here ( I am not sure...)
The situation is that I have a UDP client and server bound to the same port.
My understanding ...
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9
votes
1
answer
2k
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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 ...
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9
votes
2
answers
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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....
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9
votes
3
answers
5k
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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 ...
- 253
8
votes
6
answers
5k
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Could IPv6 make NAT / port numbers redundant?
From what I can tell, each process could get its own IP address, with loads of IP's to spare.
What would the drawbacks be?
Essentially, your host would become a router and each process is a host (in ...
- 213
8
votes
3
answers
1k
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routing between vlans not working
I need to put a Cisco router behind an ISP router.
(The ISP doesn't allow us to use their modem only.)
I've called the ISP technical service and they've set up the connection with me.
Their router ...
- 213
8
votes
1
answer
7k
views
About the inside local and outside local and inside global and outside global
I have some concept problem with the NAT. Here is the Cisco definition for the local and Global and the NAT operation.
Local address—A local address is any address that appears on the inside ...
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8
votes
1
answer
929
views
How does UDP NAT Know When To Remove The Rule
So say you are a user behind a NAT/router on an internal network. You begin sending UDP data to an internet-facing server. The packet hits your router, it inserts an entry to allow returning packets ...
- 183
8
votes
4
answers
5k
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Does IPv6 remove the need for a VPN?
I know that a VPN may be used in lots of different ways for lots of different things, so I'm not suggesting that IPv6 removes the need for a VPN completely.
I'm interested in one particular use-case:
...
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8
votes
2
answers
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NAT and UDP problems
I have a question regarding NAT, UDP and TCP.
Given a standard NAT server, is it a problem for it that UDP is connectionless? If so, why?
And does TCP or QUIC solve this problem?
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8
votes
2
answers
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How to host server in DMZ zone of an ASA
I have an ASA5525-X with 9.1.2. On it are several interfaces, but primarily I'm looking at:
(fake subnets)
inside 10.0.0.0/24, security level 100
outside 10.0.200.0/24, security level 0
DMZ 10.0.100....
- 3,052
8
votes
2
answers
2k
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SNAT vs PBR for Server Load Balancing
In an one-armed SLB configuration, SNAT is used to force return-traffic to pass through the SLB. This has one negative: simply that web logs cannot capture the true client IP unless passed in XFF (X-...
- 7,094
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votes
4
answers
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ASA use of proxy ARP for NAT
I will be performing NAT on the outside interface of an ASA to a web server within a DMZ. I would like to disable proxy-arp on all the interfaces that I can. I know that outside interface will need to ...
- 799
8
votes
1
answer
2k
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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 ...
8
votes
5
answers
8k
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Cisco Static NAT with route-maps
Update:
Seems that route maps only match on IP addresses, not on the ports. Had another situation this week on a different device, model and software version. Ended up changing the NAT statements to:
...
- 661
8
votes
2
answers
7k
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NAT with VPN Site to Site and Remote LANs with same IP address
I have a ASA5510 to connect clients to my company. I use a site-to-site IPSec VPN with a variety of vendors on the other side (Cisco, Sonicwall, Zyxel, Checkpoint, etc...).
For every remote LAN, I ...
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7
votes
7
answers
3k
views
Why is classful addressing considered waste?
I am trying to understand the addressing strategies. But there is something which I can't grasp. Maybe I am missing a very basic point, if so, I am sorry beforehand.
From my researches, let's say, if ...
- 73
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votes
3
answers
5k
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 ...
- 73
7
votes
5
answers
11k
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 ...
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votes
2
answers
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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 "...
- 1,015
7
votes
2
answers
2k
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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
...
- 431
7
votes
2
answers
19k
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Cisco ASA 8.4(3); NAT multiple ports on public IP to private IP
I have the following configuration on an ASA running 8.4 already;
object network SERVER-01
host 192.168.0.1
!
object network SERVER-01
nat (Inside,Outside) static interface service tcp 3389 5001
I ...
- 5,290
7
votes
2
answers
2k
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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 ...
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7
votes
3
answers
183
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Is IP address Subnet Renumbering needed here?
We have a router with NAT enabled on our edge. The NAT inside is 10.0.0.0/24. Now, we're running out IP blocks and we wish to change this to 10.0.0.0/22. We can do this quickly on the NAT router. But ...
- 123
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votes
4
answers
10k
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How to make IPSEC over double NAT?
I need to have a site to site VPN between two sites.
Here is the following topology for each site:
Site A: One Cisco 1921 WAN port (192.168.3.2) connected to ISP router (192.168.3.66), both the ...
7
votes
1
answer
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 ...
- 439
7
votes
2
answers
4k
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Cisco ASA: Why does static NAT block access through VPN? [closed]
TL/DR
I set up a static nat rule, so that I can use my public internet IP address to directly ssh into a dedicated machine on the inside network. As a result I cannot ssh into the dedicated machine ...
- 171
7
votes
2
answers
10k
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Source NATing Fortigate typical scenario
I have a small query with respect to NATing in Fortigate.I'm struck in particular by a scenario where the remote network allows users with a specific IP range with a specific port for RDP over a ...
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7
votes
5
answers
3k
views
PAT and Static NAT not working together?
The HQ network is using PAT to gain access to the internet, the internal webserver needs to be accessed from the internet using static NAT.
Configs:
S_HQ
!
interface FastEthernet0/1
switchport ...
- 71
6
votes
3
answers
3k
views
Does NAT violate end to end argument?
Does NAT violate end to end argument?
What does end to end argument means in this context?
6
votes
3
answers
3k
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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 ...
- 321
6
votes
4
answers
438
views
60 devices on a /29 network
My company asked me to set up a network with 60 devices (all have MAC addresses and use IPs, but they are not all computers), there is a 3rd party company that will maintain the network. They are ...
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