diff options
Diffstat (limited to 'Networking.m4')
| -rw-r--r-- | Networking.m4 | 78 |
1 files changed, 42 insertions, 36 deletions
diff --git a/Networking.m4 b/Networking.m4 index f64b341..c0bbd2b 100644 --- a/Networking.m4 +++ b/Networking.m4 @@ -256,6 +256,44 @@ of the packet. </p> facility, which means that packets may be lost, arrive multiple times, or out of order. Moreover, packets can be fragmented or defragmented. </p> +SUBSECTION(«Network Address Translation (NAT)») + +<p> IP addresses are a global resource, so each address must only be +assigned to at most one device. The <em>Internet Assigned Numbers +Authority</em> (IANA) coordinates who is entitled to use any given +range of IPv4 addresses. However, a number IP ranges, for example the +ranges 10.0.0.0-10.255.255.255 and 192.168.0.0-192.168.255.255, are +reserved for local use only so that these addresses can be assigned +in multiple local networks without interfering with each other. </p> + +<p> In a network which contains only local addresses, the devices +can communicate with each other, but they will not be able to access +public world-wide services. To illustrate how NAT works around this +restriction, consider a desktop computer in a local network which +intents to perform a web search by contacting a public web server +which is <em>not</em> a member of the local network. </p> + +<p> The desktop is configured to route packets which are not +destined for the local network through a dedicated machine, called +the <em>router</em>. The router has two IP addresses: one address +in the local network and a public NAT address. As traffic passes +from the desktop through the router to the web server, the router +alters the source address of each IP packet (the local address of the +desktop) to the public NAT address of the router, and keeps track of +all thusly forwarded connections. When a reply arrives at the router, +it uses the connection tracking data stored during the outbound phase +to determine the address in the local network to which to forward the +reply. This time the router alters the <em>destination</em> address +of the packet to the local address of the desktop and forwards the +packet to the desktop via the local network. </p> + +<p> NAT can be seen as providing a kind of privacy mechanism because +machines on the internet cannot monitor which hosts are sending and +receiving traffic. They only see the NAT address. NAT has also +downsides though: Pinpointing the source of a problem becomes harder, +and encryption becomes more difficult. For example you can not encrypt +the IP address because the router must be able to change it. </p> + EXERCISES() <ul> @@ -296,37 +334,6 @@ devices can be connected. ») HOMEWORK(« - -Illustrate how <em> network address translation </em> (NAT) works -on the basis of a web search initiated from a desktop computer in a -local network and discuss the implications that NAT has on privacy. - -», « - -<p> The desktop is configured to route packets which are not destined -for the local network through a dedicated machine, called the <em> -router</em>. In particular, all internet traffic is sent to the router. -The router has two IP addresses: one address in the local network -and a public NAT address. As traffic passes from the desktop through -the router to the web server in the internet, the source address of -each IP packet (the local address of the desktop) is changed on the -fly to the public NAT address of the router. The router tracks each -active connection. When a reply arrives at the router, it uses the -connection tracking data stored during the outbound phase to determine -the address in the local network to which to forward the reply. This -time it overwrites the destination address of the IP packet with the -local address of the desktop. </p> - -<p> NAT can be seen as providing a kind of privacy mechanism because -machines on the internet cannot monitor which hosts are sending and -receiving traffic. They only see the NAT address. NAT has also -downsides though: Pinpointing the source of a problem becomes harder, -and encryption becomes more difficult. For example you can not encrypt -the IP address because the router must be able to change it. </p> - -») - -HOMEWORK(« Run <code> tracepath wikipedia.org</code>. Explain how this command works and how it can be used to identify networking problems. ») @@ -433,11 +440,10 @@ HOMEWORK(« SECTION(«Application Layer») -<p> Application layer protocols define how the server side of a network -service communicates with clients that connect to the server by -connecting a specific TCP or UDP port. Services are often associcated -with port numbers which can be registred at the <em> Internet Assigned -Numbers Authority </em> (IANA). </p> +<p> Application layer protocols define how the server side of +a network service communicates with clients that connect to the +server by connecting a specific TCP or UDP port. Services are often +associcated with port numbers which can be registred at the IANA. </p> <p> Examples for application layer protocols which are employed on top of TCP are the <em> Hypertext Transfer Protocol </em> (HTTP, port 80) |