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• Add power over Ethernet without new switches?

  - by dannymcc

  I need to power 16 IP phones over their Ethernet connections. I am in the process of changing our switches and only the phones need PoE, everything else is powered by mains cables. I have contacted the supplier of the phones and for 16 mains leads it will be close to £300. I know it's possible to get a PoE injector that goes between the mains and the phone but I would like to do this as tidily as possible and ideally in bulk. I imagine something that looks like a switch but doesn't actually 'switch' if that makes sense. Basically I want to inject power to 16 devices at once.

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• My site cant be accessed from certain ISPs

  - by Nuker

  I am on a VPS hosted by a company in Europe. I can access my site normally, many other people i know can as well. However in the recent days i have received reports from many other people that say they cant. They get a timed out request error page. The common denominator seems to be they all have the same ISPs. I have had reports from several different countries such as Spain, Peru, Argentine etc. What can be happening?

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• Does a router have a receiving range?

  - by Aadit M Shah

  So my dad bought a TP-Link router (Model No. TL-WA7510N) which apparently has a transmitting range of 1km; and he believes that it also has a receiving range of 1km. So he's arguing with me that the router (which is a trans-receiver) can communicate with any device in the range of 1km whether or not that device has a transmitting range of 1km. To put it graphically: +----+ 1km +----+ | |------------------------------------------------->| | | TR | | TR | | | <----| | +----+ 100m+----+ So here's the problem: The two devices are 1km apart. The first device has a transmitting range of 1km. The second device only has a transmitting range of 100m. According to my dad the two devices can talk to each other. He says that the first device has a transmitting and a receiving range of 1km which means that it can both send data to devices 1km away and receive data from devices 1km away. To me this makes no sense. If the second device can only send data to devices 100m away then how can the first device catch the transmission? He further argues that for bidirectional communication both the sender and the reciver should have overlapping areas of transmission: According to him if two devices have an overlapping area of transmission then they can communicate. Here neither device has enough transmission power to reach the other. However they have enough receiving power to capture the transmission. Obviously this makes absolutely no sense to me. How can a device sense a transmission which hasn't even reached it yet and go out, capture it and bring it back it. To me a trans-receiver only has a transmission power. It has zero receiving power. Hence for two devices to be able to communicate bidirectionally, the diagram should look like: Hence, from my point of view, both the devices should have a transmission range far enough to reach the other for bidirectional communication to be possible; but no matter how much I try to explain to my dad he adamantly disagrees. So, to put an end to this debate once and for all, who is correct? Is there even such a thing as a receiving range? Can a device fetch a transmission that would otherwise never reach it? I would like a canonical answer on this.

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• Losing WLAN connections but maintaining internet connections on WIndows 7 Workgroup

  - by Di

  I have 4 computers all running Windows 7 networked in a Work group through Billion 7404vgp-m wireless router.All drivers and firmware for wireless adapters and router are up to date. Windows Firewall and Defender disabled.Disconnected ipv6. Running Nod 32 anti virus software. All have own static IP address 192.XXX.X.XXX. When I Reset the router all computers have Internet and LAN access for about 1 hour and then they will lose the LAN connection but maintain Internet connection. Resetting wireless adapters or restarting computers does nothing to fix this but resetting router will. What is causing this and how do I fix it. Thanks Di

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• Debian/OVH: How to configure multiple Failover IP on the same Xen (Debian) Virtual Machine?

  - by D.S.

  I have a problem on a Xen virtual machine (running latest Debian), when I try to configure a second failover IP address. OVH reports that my IP is misconfigured and they complaint they receive a massive quantity of ARP packets from this IPs, so they are going to block my IP unless I fix this issue. I suspect there's a routing issue, but I don't know (and can't find any useful info on the provider's website, and their support doesn't provide me a valid solution, just bounce me to their online - useless - guides). My /etc/network/interfaces look like this: # The loopback network interface auto lo iface lo inet loopback # The primary network interface auto eth0 iface eth0 inet static address AAA.AAA.AAA.AAA netmask 255.255.255.255 broadcast AAA.AAA.AAA.AAA post-up route add 000.000.000.254 dev eth0 post-up route add default default gw 000.000.000.254 dev eth0 # Secondary NIC auto eth0:0 iface eth0:0 inet static address BBB.BBB.BBB.BBB netmask 255.255.255.255 broadcast BBB.BBB.BBB.BBB And the routing table is: Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 000.000.000.254 0.0.0.0 255.255.255.255 UH 0 0 0 eth0 0.0.0.0 000.000.000.254 0.0.0.0 UG 0 0 0 eth0 In these examples (true IP addresses are replaced by fake ones, guess why :)), 000.000.000.000 is my main server's IP address (dom0), 000.000.000.254 is the default gateway OVH recommends, AAA.AAA.AAA.AAA is the first IP Failover and BBB.BBB.BBB.BBB is the second one. I need both AAA.AAA.AAA.AAA and BBB.BBB.BBB.BBB to be publicly reachable from Internet and point to my domU, and to be able to access Internet from inside the virtual machine (domU). I am using eth0 and eth0:0 because due to OVH support, I have to assign both IPs to the same MAC address and then create a virtual eth0:0 interface for the second IP. Any suggestion? What am I doing wrong? How can I stop OVH complaining about ARP flood? Many thanks in advance, DS

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• Different versions of iperf for windows give totally different results

  - by Albert Mata

  Measuring TCP output from a Windows client to Solaris server: WXP SP3 with iperf 1.7.0 -- returns an average around 90Mbit Same client, same server but iperf 2.0.5 for windows -- returns an average of 8.5 Mbit Similar discrepancies have been observed connecting to other servers (W2008, W2003) It's difficult to get to some conclusions when different versions of the same tool provide vastly different results. Example below: C:\tempiperf -v (from iperf.fr) iperf version 2.0.5 (08 Jul 2010) pthreads C:\tempiperf -c solaris10 Client connecting to solaris10, TCP port 5001 TCP window size: 64.0 KByte (default) [ 3] local 10.172.181.159 port 2124 connected with 10.172.180.209 port 5001 [ ID] Interval Transfer Bandwidth [ 3] 0.0-10.2 sec 10.6 MBytes 8.74 Mbits/sec Abysmal perfomance, but now I test from the same host (Windows XP SP3 32bit and 100Mbit) to the same server (Solaris 10/sparc 64bit and 1Gbit running iperf 2.0.5 with default window of 48k) with the old iperf C:\temp1iperf -v iperf version 1.7.0 (13 Mar 2003) win32 threads C:\temp1iperf.exe -c solaris10 -w64k Client connecting to solaris10, TCP port 5001 TCP window size: 64.0 KByte [1208] local 10.172.181.159 port 2128 connected with 10.172.180.209 port 5001 [ ID] Interval Transfer Bandwidth [1208] 0.0-10.0 sec 112 MBytes 94.0 Mbits/sec So one iperf with a 64k window says 8.75Mbit and the old iperf with the same window size says 94.0Mbit. These results are constant through repeated tests. From my testing launching iperf(old) with window size "x" and iperf(new) with window size "x" instead of producing the same or very close results produce totally different results. The only difference I see is the old compiled as win32 threads vs. pthreads but parallelism (-P 10) appears to work in both. Anyone has a clue or can recommend a tool that gives results I can trust?? EDIT: Looking at traces from (old) iperf it sets the TCP Window Scale flag to 3 in the SYN packet, when I run the (new) iperf this is set to 0 in the initial packet. A quick analysis of the window size through the exchange shows the (old) iperf moving back and forth but mostly at 32k while the (new) iperf mostly keeps at 64k. Maybe it will help somebody to connect the dots.

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• Running DNS locally for home network

  - by Roy Rico

  I have a small home network that just got larger ( New roommate, My existing roommate got a laptop (on top of her computer)j, my friends coming over with laptop, etc ). I'd like to run a local DNS server for lookups of my local network stuff (fileserver.local, windowsTV.local, machineA.local, machineB.local, appletv.local). I used to have a business line with a static IP, and run bind/named internally. However, now, I have a normal account. My ISP's DNS servers are constantly changing (for whatever reasons my ISP doesn't like to keep the same IP range for long). I need my local DNS to be automatically updated to use my ISP's DNS for external traffic, but be able to maintain an internal DNS server (getting to update the hosts file is being a hassle with every new machine on top of rebuilding existing machines with win7 or Ubuntu 9.04). Additionally, My ISP's DNS servers often crash or become unresponsive. Are there any open DNS servers that are reliable (i don't want to reconfig every day) that I could use as my primary, then if those fail, then use my ISP's? UPDATE: Also looking for each workstation to be able to use dhcp to connect, but instead of getting ISP dns servers, getting my internal one.... Thanks

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• Configuring a Genius GW-7200 Access Point

  - by alex

  I came across an access point we had a few years ago. I'm now trying to get it set up to work on our network. here are a couple of pictures: http://twitpic.com/194u06/full http://twitpic.com/194u0v/full I have plugged this into our network via the network port on the back. I set up a DHCP reservation, based on the MAC address on the back of the access point, however I cannot ping it, nor access the web interface. I've held down the reset button for 10 seconds, to see if that would do anything. Google doesn't come up with anything on the matter :-(

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• Recommend a wireless PCI card for Windows 7

  - by Dan

  I have a crummy RT2500-based 11g card which does work in Win7 with the Vista driver (3.2.0.0) but it dies about every two hours or so. Googling around has led me to conclude that Ralink drivers are basically borked, and that I need something else for a stable connection. Can anyone recommend a suitable wireless adapter? It needs to be: 802.11g - draft-N nice but not at all essential. PCI - I already have far more USB devices than can possibly be good for me. Very reliable. Money isn't an object within reason. All input gratefully received!

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• Tool for Network game party

  - by nXqd

  I'm looking for tools for a network game party ( LAN ) .This is my first time I join as a tech-support for this party. I already know some tools like Desktop Sharing, Desktop lock . Anyone suggest more tools ? And links are appreciated :)

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• How to eliminate the downtime when a dynamic IP address changes?

  - by xenon

  We currently have a number of client computers linked up to a database server (MS SQL 2008) for replication. The database server recognises the computers based on their Windows hostname. We are using dynamic IP addresses at this time because we tend to change the computers’ hardware quite frequently, and so the MAC address may be different. Unless static IP has a good way for us to manage frequent changing of MAC addresses, we are keeping it to dynamic IP. The problem with dynamic IP addresses, however, is that when a client fetches an new IP from the DHCP, ie, there is a change in the IP address, there is going to have a downtime for the hostname to reflect the new IP address, the client’s DNS cache of the hostname to reload, and also the server’s DNS cache to reload to see the new IP from the hostname. All of these have different timings and the delay can be really bad at times. Restarting the computer doesn't work all the time too. The clients are on Windows 7. How can I eliminate the amount of downtime required when there is a change in IP in the case of dynamic IP addresses?

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• How to calculate CIDR notation from entries in a routing table

  - by febreezey

  I have some entries in a routing table that were created using longest prefix matching, and I have to use those entries to determine the a.b.c.d/x notation (CIDR). This is an example entry: 11001000 00010111 00010. That was calculated from the range 11001000 00010111 00010000 00000000 through 11001000 00010111 00010111 11111111. I know the range is from IP addresses 200.23.16.0 to 200.23.23.255, but getting the /x for the subnet # doesn't make sense to me. Anyone know how to properly go about calculating it?

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• Separate computers in my apartment can't communicate to each other?

  - by Razor Storm

  In my apartment, the management provides the building with a network connection. I have my computer plugged into the ethernet coming out of the walls, and my friend who also lives in the apartment building has his computer connected to a separate ethernet jack. As far as I know our two computers are not within a LAN, and ipconfig shows that we only have external ip addresses. The problem, then, appears when we attempt make direct communication between our computers. I have some hosting server set up on my machine, and my friend is unable to connect to it via my ip address. Other people who do not live in the apartment can connect fine. Ethernet adapter Local Area Connection: IPv4 Address. . . . . . . . . . . : 204.29.113.41 Subnet Mask . . . . . . . . . . . : 255.255.254.0 Default Gateway . . . . . . . . . : 204.29.112.1 His ip: 204.29.113.104 Using a fulltunnel vpn doesn't help.

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• Rapidly changing public IP addresses on certain networks?

  - by zenblender

  I run/develop an online game where many of our users are in southeast asia. I recently went to southeast asia and made an alarming discovery. Anywhere I got internet access, whether it was via 3G, a LAN in a hotel, or wifi in a cafe, both in Singapore and the Philippines, I noticed that my IP address was changing CONSTANTLY. I mean the public IP address, not the private one. I could load a page like whatismyip.com and just hit reload and see a new IP address show up every 5-10 seconds! This has lots of consequences for my online game, as many things "break" if the IP address changes for a given user. Basically, I would like to know more about this. Is there a name for the kind of network or router or paradigm that causes this, so I can read up on it? I don't understand WHY a network would function this way. Does it do this on purpose? Is it for security reasons? Is it to anonymize and protect the identity of the users? Or is it just an "old" method that is mostly obsolete in the rest of the world? Thanks for any info that will help me to understand.

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• Determining who is running with administrator rights?

  - by Alex C.

  I work at a small non-profit organization with about 55 desktop PCs running Windows XP Pro. The domain controller is running Windows Server 2003. I have a two-part question (note that I'm a bit of a newb when it comes to network administration). Part 1: Is there some simple way that I can determine which accounts are logged in with administrator rights? Part 2: Is there a way that I can remove administrator rights from users without sitting down at each individual machine? Thanks for considering my questions.

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• ssh all machines behind a router

  - by Luc

  Hello, I have several machines on my lan. One is used as a http proxy to target web sites located on the others (that's working fine now thanks to ServerFault). On my router, Port 22 is NATed to this proxy machine. I would like to be able to access the other machines, within internet, with something like: ssh user@first_machine.my_domain.tld ssh user@second_machine.my_domain.tld Could I use the proxy machine to 'filter' the incoming ssh request and to route them to the correct machine ? (in the same way it's possible to do so for web sites using a mix of mod_proxy and namevirtualhost in Apache) Thanks a lot, Luc

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• What could cause a huge packet loss in Ubuntu 9.10, for both wired and wireless?

  - by xzenox

  I was previously using 9.04 fine (and in fact, I am posting this from my old 9.04 live cd). I tested the following install steps in a virtualbox vm prior to following the sames ones to upgrade my laptop: Download/burn ubuntu minimal cd (12mb one) Install ubuntu minimal sudo apt-get update sudo apt-get upgrade sudo apt-get ubuntu-desktop ubuntu-standard In the VM worked fine and I found myself with a working 9.10 ubuntu, network worked fine and I was able to test my backups and DropBox without a hitch (host was 9.04). When I followed the same steps on my laptop, everything worked up to after 9.10 being installed and working. As far as I can tell, everything besides eth0/wireless works. For some reason, I am unable to access the internet. Ping reports that over 99% of packets get lost (over an hour or so of pinging). This means for example that if I try hard enough, I can load a webpage but only at the cost of much patience... This happens both for a wired and wireless connection to my wrt310n (updated with latest firmware). At first I thought that it could be related to the ipv6 issues ppl have been experiencing however even after disabling ipv6 at the kernel level (through grub), I still get the issue. I do not think this is related to DNS issues or the likes since even when I ping my ISP's gateway IP, I have the same amount of packet loss. No DNS resolving should be required there. Access to my router works peachy with no packet loss there. I've tried different MTU values but to no avail. Note that this issue affects every web-enabled application: firefox, ping, synaptic, etc. The same hardware/router combo works with 9.04 but not with 9.10. In fact, when I did: sudo apt-get ubuntu-desktop ubuntu-standard after 9.10 minimal was installed, it downloaded over 400mb of packages without a hitch so my guess is that one of those packages either in ubuntu-desktop or ubuntu-standard is causing havok. Thoughts?

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• WD my cloud 4th is Super Slow

  - by Saduser

  I am using a WD my cloud 4Tb and I have read other posts about users complaining about getting only 10Mb per second. My problem is that I am getting about 100kb/s to transfer a 125gb iPhoto library. Estimated time is 11 days to transfer this file. This is unacceptable. On the back of the WD cloud I am getting a solid green light and from what I read this means that I am on a gigabyte network. I have mac book pro running Mac OS Mavericks. I have tried 4 different cables and turned off my router firewall. I don't run anti-virus nor any firewall on the mac. Other things I have checked: direct connection to both router and WD cloud device. Tried wireless but it is even slower. Previously I was able to transfer a 55Gb iPhoto library in 14 hours which I felt was acceptable. I figured it would take approximately double the time to transfer the 125gb file but 11 days is ridiculous. Any other suggestions? Anything else I can check (how to check it) what is the bottle neck?

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• Managing DHCP with Cobbler and multiple NICs

  - by William

  Hi, I'm trying to setup Cobbler for PXE booting and I want it to also manage DHCP. The issue is I only want one of the two available NICs to manage DHCP. Is there a way to specify which NIC Cobbler will use for DHCP? Thank you.

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• Server Fault Wiki: How does Subnetting Work?

  - by Kyle Brandt

  How does Subnetting Work, and How do you do it by hand or in your head? Can someone explain both conceptually and with several examples? Server Fault gets lots of subnetting homework questions, so we could use an answer to point them to on Server Fault itself. If I have a network, how do I figure out how to split it up? If I am given a netmask, how do I know what the network Range is for it? Sometimes there is a slash followed by a number, what is that number? Sometimes there is a subnet mask, but also a wildcard mask, they seem like the same thing but they are different? Someone mentioned something about knowing binary for this? Not looking for links to other sites (unless maybe you have one post with a bunch of good ones). I already know how to subnet, I just thought it would be nice if Server Fault had a generic subnetting answer.

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• Why does just splitting an Ethernet cable not work?

  - by Sin Jeong-hun

  I thought the Ethernet is logically a one-line communication bus (for argument's sake, I am excluding hubs). All machines attached on the bus hears the same signals and the machines themselves try to avoid collisions by randomly backing off. http://computer.howstuffworks.com/ethernet6.htm If so, why would splitting one Ethernet line from my home router into two and connecting two computers not work? Why do I have to add a switch to it? *What the Internet said would not work. [4 port home router] ------[one Ethernet cable]-----[simple splitter]======[two computers] *What the Internet said I should do [4 port home router] ------[one Ethernet cable]-----[switch]======[two computers] Is this because of the signal degradation (reduced electric current)? Thank you for all the answers! The reason why I did not just use the two ports of my home router is... The 4-port gigabit router is in my room, and I had put a computer in another room (also my room, though). Since a wired network is far more reliable and secure, I had bought a long Ethernet cable and and connected the computer to the router. Now I was thinking about adding another computer to that room. I could buy another long Ethernet cable, but then there will be two cables between the rooms. The one line already is a minor annoyance, so I thought if I could share the one line between the two computers in that room. A switch would work, but it requires power and is a little bit pricey. That is why I wondered why it would not work to simply split the physical Ethernet cable. Apparently I do not completely understand how Ethernet and a switch work. I just have some bit of knowledge I heard in my college class.

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• How to connect 2 routers (Asmax and D-link) RJ11 vs RJ45 issue

  - by piobyz

  I just bought a new router, D-link DSL 2641B and want to connect it to another one, provided by my ISP, Asmax AR 804MP. Previously, I had Linksys WRT350N, and there was no problem, while I had Ethernet cable plugged in to one of LAN ports in Asmax and INTERNET(RJ45) port in Linksys, connection used PPPoE protocol -- worked OK. D-link has DSL(RJ11) port (which I don't want to use as Asmax replacement, while there is a separate Ethernet cable with a TV plugged to Asmax, which I don't want to configure from scratch on D-link). How should I connect my new D-link to work with Asmax? Via DSL port? Via one of the LAN ports (in which case I probably should change the purpose of this port in the config, I guess?). I tried connecting D-link both ways: LAN(ASMAX) to LAN(DLINK) LAN(ASMAX) to DSL(DLINK) (using RJ11 - RJ45 cable) I hope there is some setting in the DLINK's config that I overlooked. I haven't tried to see what's in ASMAX's config, but I guess I don't need to change anything there, while Linksys worked just fine? The only difference I see, is that D-link has RJ11 DSL port as WAN, and Linksys has RJ45 (called by them INTERNET) as a main WAN port.

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• Are there any wireless webcams/cameras that Windows will recognize as a capture device?

  - by Keithius

  I'd like to have a webcam in a different room from my computer, and the distance means USB is out of the question. I know there are many wireless cameras, but what I can't seem to find out is if any of them would be recognized by Windows as a capture device (just like a locally connected USB webcam). Most of the wireless cameras I can find (e.g., D-Link DCS920; Cisco-Linksys WVC54GCA, etc.) can all stream video directly from the camera itself, which is fine if you're using the camera as a "security" camera (for private use only), but not for other uses (say, sending the video to an online video streaming service, e.g., Ustream). It seems like this should be possible; after all, wireless (WiFi) printers with scanners are recognized by Windows. Are there any wireless (WiFi) cameras out there that would be recognized by Windows as a capture device in the same way as a USB webcam would? Alternatively, a camera that's not wireless (e.g., connects via Ethernet) would do the trick too - but I imagine if anyone is going to make a remote camera like this, they'd go the extra step and make it wireless, too.

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• Connectiong adsl router/modem and router with bridgemode

  - by Zvonko Telefonko

  I have one adsl modem/router which is not "top" of the line and it lack allot of options which I need. I was able to acquire one Cisco router recently which has all options that I need ( like DMZ, VPN, port forwarding, etc). I'm interested, if I connect the old modem/router to new Cisco router using bridge mode, will I be able to use all the features on the Cisco? For instance, the old router is lacking of port forward options. Does this mean that I will not be able to use port forwarding on Cisco router either or, since I will be using bridge mode, this will not affect Cisco router and it will work as the modem is in him? thank you

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• Dlink DIR-615 suddenly stops working - Orange internet light

  - by zm15

  I unplugged my Dlink DIR-615 router last night from the wall due to a storm rolling in. I've done this countless times, no problem. However, when I went to plug it in and use the internet today, nothing. Check everything, cycled everything. Hard reset the router, nothing. The little globe on the front is red/orange, and it should be green. Windows gives me an error of a "DNS Issue", and the internet works when connected directly to the modem. How can I fix this issue? Why would it suddenly stop working?

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