Ip Aliasing allows us to associate more than one ip address to the same interface. My question is how can one bind and hence receive the data from all of the addresses associated to an interface? Is there some option like INADDR_ANY available for the purpose?
Always remember that bind(2) does not bind to interfaces, but addresses.
Each socket generally only stores exactly one binding, even if that is 0.0.0.0 port 0. It is just that 0.0.0.0, :: and port 0 are taken as wildcards when checking incoming requests. As such, you will need one socket for non-wildcard addresses.
See setsockopt SO_BINDTODEVICE if you really need interface binding, but that is in general not the right thing to do in programs other than e.g. tcpdump, as it will inhibit contacting over different interfaces even if they allow reception. For example, if your own host has 192.168.0.1 as an address on a private LAN, binding to eth1 will make it impossible to connect to 192.168.0.1 from .0.1 itself over lo. Hence, device binding is usually undesired.
Try binding to the interface, using setsockopt and SO_BINDTODEVICE.
Related
I have a language monitor that I am trying to query the printer from.
First let me apologize for the possible confusion since "port" means 2 things in this description. There is the one use that refers to the port that the printer is configured to use, which could be TCP, USB, etc. And then there is the use of port that refers to the port address to send data to when communicating with the printer's IP address.
I need to be able to specify different port addresses to send different custom queries to a printer over the same IP that are specific to it's firmware. I can't find any examples or documentation on what the standard way is to do this communication... I can extract the IP address and open a net socket, but I am not sure if this is the appropriate way to handle this communication. It's not uncommon for printers to send status over one port, and print data over another. If i want to write to the Default port I can use pfnWritePort and pfnReadPort, but these don't allow me to specify the actual port.. it uses whatever the driver is configured as.
Can anyone provide some guidance or examples of how I should do this from my language monitor?
EDIT: As an example for clarification, all commands are sent to the same IP, but depending on the command/query I need to send, the TCP port needs to change. The way I am handling it now is opening up a net socket with the same IP and different port numbers for data and status channels).
You should be required to write an app that would be able to reconfigure driver. Ideology of OS is that EACH real device would corresponds to instance of driver and\or interface. Which might be an elevated action, because it requires to create new printer interface("port" in Windows GUI terms) and change driver settings.
During development of an IpAddress library's part, I'm confronted to a minor dilema.
How to name my function testing the address to be a LocalHost / Loopback.
What is the difference between this 2 designations?
In other libs , they make this choices:
Boost.asio -> is_loopback
Qt -> isLoopback
wxWidget -> IsLocalHost
Why do they call isLoopback a test like address == "::1" ??
ANSWER:
"localhost" is usually an alias for the "loopback" interface. They can and are often used interchangeably.
Subquestion: Is it the same definition between IPv4 and IPv6?
The previous answer is not entirely correct.
Loopback +interface+ may have configured multiple IP addresses, not only from localhost network. It is a common practice to put non-local address on loopback interface in e.g. dynamic routing, where you don't want to lose routes to router's IP in case any interface goes down.
On the other hand, loopback IPv4 +network+ is defined by IANA as 127.0.0.0/8. Surprisingly, for IPv6 they reserved only ::1/128 address.
To answer your question: if you want to check only addresses, I'd pick isLocalhost(). And to be a bit zealous, I'd check there for the whole network - I happened to see 127.0.0.2 a few times...
On my package 1, under the info it says (source)54841 > 80(destination). May I know what are these terms mean and why these particular ports are being used. i know that for tcp, they uses 80 for destination port. but is there a particular reason? Thank you
In fact, there are two questions with two different answers.
Firstly, you have to be exact: The port definition is part of the Internet Proctocol (commonly called TCP/IP) application layer. The tcp protocol is a protocol of the underlying transport layer, so the definition / use of port 80 is not defined for tcp, but rather for the http application protocol (while the actual port usage takes place in the transport layer).
Regarding the destination port, you nearly gave the answer yourself: For well defined application protocols, there were defined well known ports. The list is maintained by IANA (https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml). Usually, the ports were defined in the privileged low number range (up to 1024). When that range became to full, there were also higher port numbers assigned.
The reasoning behind the well defined port numbers is, that services can only listen on specific ports, and if the numbers were known by convention, you had to memorize them along with the server adress. For your example, HTTP, that means, that if you start a request for http://www.example.com, your browser (or other software) knows that http usually uses port 80, connects to that port to get the html page. You can still run http servers on different ports (say, 12345), but than, the user had to enter http://www.example.com:12345 to reach the server. You can see that using well defined ports is helpful here.
For the source port, it is a completely different story. As transport layer connections usually use ports for multiplexing/demultiplexing on both source and destination, every connection must also have a source port. The lower port numbers can not be used for this purpose, as on one hand, they are often used for listening services, and on the other hand, their usage is privileged on some operating systems, so normal users cannot use them at all. For this reasons, IANA assigned the port range from 49152 to 65535 (2^15+2^14 to 2^(16−1)) for that purpose. Most operating systems will select one of this ports for outgoing connections source port. The selection is, however, short lived - when the connection is closed, the port is released, and the next connection can use an other port.
Different websites uses different ports, like Codecademy uses localhost:8000 in its AngularJS and Ruby On Rails tutorials. So, I want to know what is the use of this 8000 in localhost:8000. Thanks in advance :-)
This is not specific to one framework, it's a much lower level. From Wikipedia:
In computer networking, a port is a software construct serving as a communications endpoint in a computer's host operating system. A port is always associated with an IP address of a host and the protocol type of the communication. It completes the destination or origination address of a communications session. A port is identified for each address and protocol by a 16-bit number, commonly known as the port number.
Specific, well-known port numbers are often used to identify specific applications and services. Of the thousands of enumerated ports, 1024 well-known port numbers are reserved by convention to identify specific service types on a host. The protocols that primarily use ports are the Transport Layer protocols, such as the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) of the Internet Protocol Suite.
In the client-server model of application architecture, ports are used to provide a multiplexing service on each port number that network clients connect to for service initiation, after which communication is reestablished on another connection-specific port number.
I assume, there's a task runner like grunt or gulp serving the page via BrowserSync (or similar). They use a different port than 80 to not interfere with an already occupied port by a local web server (apache, nginx,...).
This is just a port which rails is listening to. It depends on how you configure your rails server, and, IMHO does not mean anything useful. Sometimes you have to assign service to a different port because default port is occupied by some other service. Sometimes it is done by security reasons, so the hacker from outside world has to know the port you are using. But it's actually not very hard to know
Just to add to what the others have said: all network communications require an ip address (which can be got from a domain name like www.google.com) and a port number. However, if a port number is not supplied then the http server uses the default: this is usually port 80. So, if you were to go to "localhost" without a port, you are effectively saying "localhost:80". Your computer probably doesn't know what to do with this. If you say "localhost:8000", and there's a rails server there, then it will handle the request.
I'm using a real machine (hp procurve) for my project, I need to send message of other protocol format, OSPF for instance, instead of flows, from controller side to OpenFlow switch through socket(by specifying ip address and port of the OF switch).
But everytime I try to do this, I get "Connection refused" error message, I guess that it might be that the port on OpenFlow switch I'm sending the message to is not listening, so I think I might need to use the same port for the sending which OpenFlow switch uses to talk to the controller, like the port 51067 in the log info :
Switch:192.168.1.11:51067 is connected to the Controller
My question is, how do I retrieve the port information on the controller side, since it is changing every time I restart it? I couldn't find this information.
Or am I going the wrong direction that I need to go another way around instead of sending the message using socket?
Thanks a lot in advance, any suggestions will be appreciated.
jonesir
I think you are misunderstanding the nature of networking ports, protocol numbers, and protocols such as OSPF. Let me clear those up:
Port numbers: Usually, there is exactly one application listening on a single port: The operating system/networking stack checks each packet of certain types (e.g. TCP or UDP) for the port number and then passes the packet to the application that registered itself for that specific port. If the application cannot handle the received packet then usually it will just ignore it or log an error.
Aside: It is possible for two applications to communicate on the same port only if you put some sort of multiplexing application before both (usually a reverse proxy, possibly a TCPMUX application). This multiplexing application would take incoming packets, determine what type of packet it is and then pass it to the correct application.
Protocol numbers: The protocol number is a field inside an IP packet that tells the networking stack what type of data is contained inside. For example, TCP is protocol 6, ICMP is 1, and OSPF is 89.
OF switches: Now, logically an OF switch consists of two components: 1) the switching fabric (which includes the physical ports and OF flow tables), and 2) a separate physical port to for out-of-band control, with several applications running behind it. One of these applications is the OpenFlow application, which in your case happens to listen on port 51067. But in real switches, other applications might also be running on different ports, e.g. a web interface running on port 80 for maintenance etc.
OSPF: If you now wanted to talk to the application serving the web interface, you'd send a TCP packet with destination port 80 from your controller to the switch. Similarly, if you'd like to install a new flow, you'd send an TCP packet with port 51067 in your case. OSPF is quite different, as it directly uses IP packets and does not use port numbers. To process an OSPF packet, an application needs to use a raw socket to process the incoming IP packets that have protocol number 89, and skip all others. See also the raw manpage here. This will already be built into your OF switch.
Thus, if you want to send an OSPF packet to the OF switch (and your OF switch supports OSPF on the separate physical port!), you'd just send an OSPF IP packet to the switch's IP address (192.168.1.11), no port needed!
Note that the separate physical port might not support all of the features of the other ports on the OF switch, as they are not intended for the same uses.