Closed. This question is off-topic. It is not currently accepting answers.
Want to improve this question? Update the question so it's on-topic for Stack Overflow.
Closed 9 years ago.
Improve this question
So, this appears, on the surface, to be a network admin (serverfault) question, but I'm looking for a lower level answer from a network hacker type.
I was pretty much oblivious to how networks actually work in real life until I started my summer internship. Then, by way of having no other option (internship is at a pretty networking-centric place and I have to put together testbeds for testing [among other things] networks), I became familiar with them. For one thing, the fact that there's no "This goes out to the internet!" port on commercial switches was kind of surprising, until you reasoned about how it works (starts out like a hub til it 'learns' where ips are in terms of the physical port, i guess?).
And after this home-crafted self-discovery (or possibly, error in thinking), I'm back at the extended stay hotel and looking at my cheap little home switch, and it has an uplink port.
Now my question to you, Network hackers (in the good way), is why?
The "uplink" port on your SOHO switch is internally crossed over. It relieves you of having to use a crossover cable to connect two switches. That is the only difference.
BTW: There isn't a "this goes out to the internet" port on SOHO switches either. You're confusing switches and routers/gateways. This confusion may be encouraged by manufacturers putting the two logically separate devices in one piece of hardware, e.g., a router with a 4-port switch. While we're at it, a wireless router w/ 4 port switch is actually logically three separate devices (router, switch, and access point).
BTW #2: A switch (well, except for layer 3 switches, which arguably are only switches to the marketing department) actually learns where MAC addresses are. It neither knows about nor cares about IP.
Uplink ports can be thought of special ports for inter-switch connections. Sometimes they may have a higher speed (1G instead of 100M for example). Or they are interchangeable (laid out as modules).
Some have multiple uplink ports (I had one with two), so you may have redundancy or multiple switched connected this way with the same logic (where is the mac address (on wthich other switch)?).
Related
Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.
Closed 7 years ago.
This question does not appear to be about a specific programming problem, a software algorithm, or software tools primarily used by programmers. If you believe the question would be on-topic on another Stack Exchange site, you can leave a comment to explain where the question may be able to be answered.
This question does not appear to be about a specific programming problem, a software algorithm, or software tools primarily used by programmers. If you believe the question would be on-topic on another Stack Exchange site, you can leave a comment to explain where the question may be able to be answered.
Improve this question
I have a small doubt regarding the LAN as i Havesome pcs in my office i want to connect them internally with the little cable connection but i don't want to use any internet activity from them.(purpose is the share the data internally and no use of internet).
And i have some more selected people who want to use the internet access so i want to give some special access for internet for that selected laptops.
Iam a kid in networks as i don't have any idea how i can start and move with the project suggestions are mostly accepted
You can do the following :-
Establish a small LAN connection in your office which will consist of those selected PC's which are not intended to run internet at all! You can simply establish LAN connection using routers and switches! Then,develop a small web-server like thing on one of the PC's which will work as server and the rest will work like clients! You can simply set up a distributed server which will take care of synchronisation things too(but, that is not advisable for a basic OR a newbie)!
But, simply multiple-clients and a server is what you need to
establish using LAN connection for and make network file-sharing access permissions for all the systems... There are several softwares to transfer files and internally communicate like a small mail-server intended for OS like Windows,Linux,etc.
Next for those laptops which you wanna connect to internet---please establish a source of internet like any ISP and so! Next,a gain establish a small LAN connection among those PC's which you want to connect to internet to. That's it,VOILA!
Next step of yours would be simply to configure DNS setting,IP-Address of the ISP,Subnet Mask and Gateway and that is damn easy. You simply need to add it to the router settings through which all of your systems,which are intended to access internet,would be connected. If you want to achieve the first thing with these PC's, then simply establish a local web-server or mail server for file transfer or mails,etc. locally within the office.
Another possibility :-
Establish the web server communication with all the PC's connected. Connect all the PC's and laptop to router's and switches as desired. Keep a note of IP-Address of all the PC's and laptops. Now, install a web-filter/firewall which will restrict users from accessing internet based on their hostname & IP-Address. Remember for this to take place, all the systems must have static IP-Address allocation,not the DHCP configuration!
I guess these are some of the possible steps. But,there can be several effective steps too...
Best wishes from my side!
Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 8 years ago.
Improve this question
If Chris and Pat want to exchange a text message, they send and receive via their network providers, which charge them for a connection.
If Chris and Pat are both located in New York City, and there are enough wireless devices between Chris and Pat all close enough to each other to form a continuous chain, is it possible for all those devices to be programmed to cooperatively forward packets amongst each other, bypassing the need for network providers?
It would seem the "address" of each device would have to include current geographic coordinates, and devices would have to report their movements frequently enough so routing attempts could still find them, but the speed and capacity of devices nowadays could handle that, right?
Would such a network be viable? Does it already exist or has it been attempted? Is there some kind of inherent programming problem that is difficult to overcome?
There are a few interesting things here:
Reachability. At least you need to use a technology that can do ad-hoc and peer-to-peer networking. Of those technologies only bluetooth, NFC and WiFi are more or less often implemented. Of those again only wifi currently may have the strength to connect to devices in other houses or to the street, but even there typical ranges are 30-60m (and that's for APs, it might be lower for UEs).
Mobility. ANY short-range wireless communication protocol has difficulties with fast-moving devices. It's simple math, suppose your coverage is 50m in diameter, if you move at about 20km/h or 5.5m/s, you have less than 10s to actually detect, connect and send data while passing this link. Oh, but then we did not consider receiving traffic, you actually have to let all devices know that for the next 10s you want to receive data now via this access network. To give an example, wifi connectivity times with decent authentication (which you need for something like this) alone takes a few seconds. 10s might be doable, but as soon we talk about cars, trains, ... it's becoming almost impossible with current technology. But then again, if you can't connect to those, what are the odds you will cross some huge boulevards with your limited reachability?
Hop to hop delays. You need a lot of those. We can fairly assume that you need at least a hop each 20-30m, let's average at 40 hops/km. So to send a packet over lets say 5km you'd need 200 hops. Each hop needs to take in a packet (L2 processing), route it (L3 processing) and send it out again (L2 processing). While mobile devices are relatively powerful these days I wouldn't assume they can handle that in the microseconds routers do. Next to that in a wireless network you have to wait for a transmission slot, which can actually take in the order of ms (each hop!). So all in all, odds are huge this would be a terribly slow network.
Loss. Well, this depends a bit on the wireless protocol, either it has its own reliable delivery protocol (which will make the previous point worse) or it doesn't. In that last case, suppose your wireless link has about .1% loss, or 99.9% no-loss, this would actually end up with an 18.1% loss rate for the 200 hops considered previously ( (1-0.999**200)*100) This is nearly impossible to work with in day-to-day communications.
Routing. lets say you need a few millions of devices and thus routes. For traditional routing this usually takes some very heavy multicore routers with loads of processing power. Let's just say mobile devices (today) can't cut that yet. A purely geographically based routing mechanism might work, but I can't personally think of any (even theoretical) system for this that works today. You still have to distribute those routes, deal with (VERY) frequent route updates, avoid routing loops, and so on. So even with that I'd guess you'd hit the same scale issues as with for example OSPF. But all-in-all I think this is something that mobile devices will be able to handle somewhere in the not-so-far future, we're just talking about computing capacity here.
There are some other points why such a network is very hard today, but these are the major ones I know of. Is it impossible? No, of course not, but I just wanted to show why I think it is almost impossible with the current technologies and would require some very significant improvements, not just building the network.
If everyone has a device with sufficient receive/process/send capabilities, then backbones (ISP's) aren't really necessary. Start at mesh networking to find the huge web of implementations, devices, projects, etc., that have already been in development. The early arpanet was essentially true peer-to-peer, but the number of net nodes grew faster than the nodes' individual capabilities, hence the growth of backbones and those damn fees everyone's paying to phone and cable companies.
Eventually someone will realize there are a million teenagers in NYC that would be happy to text and email each other for free. They'll create a 99-cent download to let everyone turn their phones and laptops and discarded devices into routers and repeaters, and it'll go viral.
Someday household rooftop repeaters might become as common as TV antennas used to be.
Please check: Wireless sensor network
A wireless sensor network (WSN) of spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, pressure, etc. and to cooperatively pass their data through the network to a main location
Closed. This question is off-topic. It is not currently accepting answers.
Want to improve this question? Update the question so it's on-topic for Stack Overflow.
Closed 12 years ago.
Improve this question
Scenario: I have two ADSL modem that are connected to to different ISPs. Each has 256KBps Speed.
Question:Is it possible to have 512KBps speed?(I have one PC that can be host any OS)
Is any special appliance essential for doing that?
Thanks in Advance,
Ashkan.
This is called multihoming or load-balancing.
The simplest way to do this would be to buy a router with two WAN ports that supports load balancing. These are generally expensive.
Alternatively you can set up a computer with 3 network interfaces to do the routing for you.
Windows
Using regedit navigate to
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\NetBT\Parameters
Create 32-bit dword value "RandomAdapter" with a value of 1
You will need to set the "metric" value of the different adapters if you find traffic is still favouring one connection over the other.
From my answer on serverfault, the
"route" command is used to set this metric. The basic syntax is;
route ADD <destination> <subnet mask> <gateway (vpn dhcp server)> <metrix> IF <interface number> -p
There's some tutorials floating around here and there.
Linux
See the answers on serverfault
RJFalconer is right, but you should know that if you do this, no single TCP connection will be able to get more than 256kBps. It's much like SMP in that manner.
You may also run into trouble with (web) applications and protocols that assume every user has a single IP address at any one time. If you can replace the two connections with a single faster one, that would be vastly preferable.
Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.
This question does not appear to be about programming within the scope defined in the help center.
Closed 2 years ago.
Improve this question
I wanted to know if any such system already exists for the average open-source user. With all of the net neutrality arguments around and with the cost of broadband likely to go up in the future. It seems like a good idea for an open-source protocol that allows standard consumer routers to operate together and form a mesh network with other consumer routers close by.
Likely possible that with enough nodes in close enough proximity and a good abstraction we could get something good going.
You could always use WDS nodes (like a repeater, kinda).
I use it in my Buffalo AirStation with DD-WRT installed (any router that can load DD-WRT would work).
www.dd-wrt.com
Not sure on the scalability of it though. And the APs would have to be in reach of each other. They could run on separate SSIDs though.
Edit: here's the DD-WRT Wiki page about WDS: http://www.dd-wrt.com/wiki/index.php/WDS
WDS is not meant for and will not scale to more than a few nodes.
There has been extensive work on mesh routing protocols such as BATMAN-ADV, OLSR, BMX and 802.11s. These are all supported on OpenWRT which supports a very large number of consumer wireless routers
There are also many large scale deployments such as freifunk and deployments by The Village Telco
Just to add more info, batmand (layer 3) or batman-adv(layer 2) can run on almost anything with a resemblance of linux, I have managed to get it working on android devices (running cyanogenmod mostly), raspberry's, laptops, foneras, .... basically anything that has or allows a wireless card with ad-hoc mode and a linux-based operating system.
Freifunk Luebeck uses D-Link 300 with batman-adv
Closed. This question is off-topic. It is not currently accepting answers.
Want to improve this question? Update the question so it's on-topic for Stack Overflow.
Closed 10 years ago.
Improve this question
I've recently become aware that there's a distinction between IP multicasting (which apparently doesn't work that well on the public internet) and application multicasting (which is apparently used in IRC and PSYC, per http://en.wikipedia.org/wiki/Multicast).
Is there a good tutorial on implementing application-level multicasting?
I thought the whole point of multicast was to reduce bandwidth for common network segments, so it's hard for me to understand what application-level multicast does.
The purpose of IP level multicasting is to reduce bandwidth for common network segments where many users wish to receive the same traffic. It's usually limited to one particular subnet and an IP router won't propagate the multicast beyond the subnet. This is done for scalability reasons - it wouldn't be a good idea to allow one host to originate multicast packets which are propagated to every IP address on the internet.
There are different ways to think of "application level" multicasting. One approach is to build a multicast tree using the host computers participating in the multicast. Dijkstra's algorithm could be used to do this (Wikipedia has a reasonable description of this). However, maintaining the list of participating computers - and keeping the tree up to date - can be a fair amount of work if hosts are joining and leaving the network at a substantial rate. And you probably don't have a good estimate of hop cost available at the application level.
Another approach you should review is the flooding algorithm used in the Gnutella network's query routing protocol. (Wikipedia also has a good description of this.) This approach alleviates the need to build a multicast tree, but it has the downside of generating more network traffic. In fact, a LOT more network traffic, as the traffic grows with the square of the number of nodes, i.e. O(n**2).
Another example of application multicasting is using JGroups in Amazon EC2 or Google App Engine as they do not support IP multicast but developers want to use multicasting functionality.