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• Can not access Internet (DNS names do not resolve) after update today

  - by Aras

  I have been using Precise for a few weeks now for work with no problem. Today, I am not able to access any website using either wired or wireless connections. I installed the updates today which included nautilus, xserver, and a new kernel (3.2.0-24). After restarting I no longer was able to browse the Internet using firefox or chrome. Trying to ping google in terminal gives ping: unknown host google.ca I have tried: Connecting to wireless or wired networks (both working on other machines) Restart the machine and boot with previous Kernel Manually configure opendns on my wired connection Restart the network and the laptop and the wireless card Without any success so far. I am not sure where to go next. Please let me know the cause of the issue or help me troubleshoot it. Note that the laptop does receive an ip address, and it can ping ip address of google.ca (74.125.127.94) but not the domain name, or any domain name for that matter. This system was upgraded from 11.10 to 12.04 more two weeks ago.

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• Querying Networking Statistics: dlstat(1M)

  - by user12612042

  Oracle Solaris 11 took another big leap forward in networking technologies providing a reliable, secure and scalable infrastructure to meet the growing needs of today's datacenter implementations. Oracle Solaris 11 introduced a new and powerful network stack architecture, also known as Project Crossbow. From Solaris 11 onwards, we introduced a command line tool viz. dlstat(1M) to query network statistics. dlstat (for datalink statistics) is a statistics querying counterpart for dladm(1M) - the datalink administration tool. The tool is very easy to get started. Just type dlstat on a shell prompt on Solaris 11 (or later). For example,: # dlstat LINK IPKTS RBYTES OPKTS OBYTES net0 834.11K 145.91M 575.19K 104.24M net1 7.87K 2.04M 0 0 In this example, the system has two datalinks net0 and net1. The output columns denote input packets/bytes as well as output packets/bytes. The numbers are abbreviated in xxx.xxUnit format. However, one could get the actual counts by simply running dlstat -u R (R for raw): # dlstat -u R LINK IPKTS RBYTES OPKTS OBYTES net0 834271 145931244 575246 104242934 net1 7869 2036958 0 0 In addition, dlstat also supports various subcommands dlstat help The following subcommands are supported: Stats : show-aggr show-ether show-link show-phys show-bridge For more info, run: dlstat help {default|} I will only describe couple of interesting subcommands/options here. For a comprehensive description of all the dlstat subcommands refer dlstat's official manual . For NICs that support multiple rings (e.g. ixgbe), dlstat show-phys -r allows us to query per Rx ring statistics. For example: dlstat show-phys -r net4 LINK TYPE INDEX IPKTS RBYTES net4 rx 0 0 0 net4 rx 1 0 0 net4 rx 2 0 0 net4 rx 3 0 0 net4 rx 4 0 0 net4 rx 5 0 0 net4 rx 6 0 0 net4 rx 7 0 0 In this case, net4 is just a vanity name for an ixgbe datalink. This view is especially useful if one wants to look at the network traffic spread across all the available rings. Furthermore, any of the dlstat commands could be run with -i option to periodically query and display stats. For example, running dlstat show-phys -r net4 -i 5 will emit per Rx ring stats every 5 seconds. This is especially useful while analyzing a live system. Similarly, dlstat show-phys -t could be used to query per Tx ring stats. -r and -t could also be combined as dlstat show-phys -rt to query both Rx as well as Tx stats at the same time. Finally, there is also a quick way to dump ALL the stats. Just run dlstat -A. You probably want to redirect this output to a file because you are going to get a whole load of stats :-).

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• Linux e1000e (Intel networking driver) problems galore, where do I start?

  - by Evan Carroll

  I'm currently having a major problem with e1000e (not working at all) in Ubuntu Maverick (1.0.2-k4), after resume I'm getting a lot of stuff in dmesg: [ 9085.820197] e1000e 0000:02:00.0: PCI INT A disabled [ 9089.907756] e1000e: Intel(R) PRO/1000 Network Driver - 1.0.2-k4 [ 9089.907762] e1000e: Copyright (c) 1999 - 2009 Intel Corporation. [ 9089.907797] e1000e 0000:02:00.0: Disabling ASPM L1 [ 9089.907827] e1000e 0000:02:00.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16 [ 9089.907857] e1000e 0000:02:00.0: setting latency timer to 64 [ 9089.908529] e1000e 0000:02:00.0: irq 44 for MSI/MSI-X [ 9089.908922] e1000e 0000:02:00.0: Disabling ASPM L0s [ 9089.908954] e1000e 0000:02:00.0: (unregistered net_device): PHY reset is blocked due to SOL/IDER session. [ 9090.024625] e1000e 0000:02:00.0: eth0: (PCI Express:2.5GB/s:Width x1) 00:0a:e4:3e:ce:74 [ 9090.024630] e1000e 0000:02:00.0: eth0: Intel(R) PRO/1000 Network Connection [ 9090.024712] e1000e 0000:02:00.0: eth0: MAC: 2, PHY: 2, PBA No: 005302-003 [ 9090.109492] e1000e 0000:02:00.0: irq 44 for MSI/MSI-X [ 9090.164219] e1000e 0000:02:00.0: irq 44 for MSI/MSI-X and, a bunch of [ 2128.005447] e1000e 0000:02:00.0: eth0: Detected Hardware Unit Hang: [ 2128.005452] TDH <89> [ 2128.005454] TDT <27> [ 2128.005456] next_to_use <27> [ 2128.005458] next_to_clean <88> [ 2128.005460] buffer_info[next_to_clean]: [ 2128.005463] time_stamp <6e608> [ 2128.005465] next_to_watch <8a> [ 2128.005467] jiffies <6f929> [ 2128.005469] next_to_watch.status <0> [ 2128.005471] MAC Status <80080703> [ 2128.005473] PHY Status <796d> [ 2128.005475] PHY 1000BASE-T Status <4000> [ 2128.005477] PHY Extended Status <3000> [ 2128.005480] PCI Status <10> I decided to compile the latest stable e1000e to 1.2.17, now I'm getting: [ 9895.678050] e1000e: Intel(R) PRO/1000 Network Driver - 1.2.17-NAPI [ 9895.678055] e1000e: Copyright(c) 1999 - 2010 Intel Corporation. [ 9895.678098] e1000e 0000:02:00.0: Disabling ASPM L1 [ 9895.678129] e1000e 0000:02:00.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16 [ 9895.678162] e1000e 0000:02:00.0: setting latency timer to 64 [ 9895.679136] e1000e 0000:02:00.0: irq 44 for MSI/MSI-X [ 9895.679160] e1000e 0000:02:00.0: Disabling ASPM L0s [ 9895.679192] e1000e 0000:02:00.0: (unregistered net_device): PHY reset is blocked due to SOL/IDER session. [ 9895.791758] e1000e 0000:02:00.0: eth0: (PCI Express:2.5GB/s:Width x1) 00:0a:e4:3e:ce:74 [ 9895.791766] e1000e 0000:02:00.0: eth0: Intel(R) PRO/1000 Network Connection [ 9895.791850] e1000e 0000:02:00.0: eth0: MAC: 3, PHY: 2, PBA No: 005302-003 [ 9895.892464] e1000e 0000:02:00.0: irq 44 for MSI/MSI-X [ 9895.948175] e1000e 0000:02:00.0: irq 44 for MSI/MSI-X [ 9895.949111] ADDRCONF(NETDEV_UP): eth0: link is not ready [ 9895.954694] e1000e: eth0 NIC Link is Up 10 Mbps Full Duplex, Flow Control: RX/TX [ 9895.954703] e1000e 0000:02:00.0: eth0: 10/100 speed: disabling TSO [ 9895.955157] ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready [ 9906.832056] eth0: no IPv6 routers present With 1.2.20 I get: [ 9711.525465] e1000e: Intel(R) PRO/1000 Network Driver - 1.2.20-NAPI [ 9711.525472] e1000e: Copyright(c) 1999 - 2010 Intel Corporation. [ 9711.525521] e1000e 0000:02:00.0: Disabling ASPM L1 [ 9711.525554] e1000e 0000:02:00.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16 [ 9711.525586] e1000e 0000:02:00.0: setting latency timer to 64 [ 9711.526460] e1000e 0000:02:00.0: irq 45 for MSI/MSI-X [ 9711.526487] e1000e 0000:02:00.0: Disabling ASPM L0s [ 9711.526523] e1000e 0000:02:00.0: (unregistered net_device): PHY reset is blocked due to SOL/IDER session. [ 9711.639763] e1000e 0000:02:00.0: eth0: (PCI Express:2.5GB/s:Width x1) 00:0a:e4:3e:ce:74 [ 9711.639771] e1000e 0000:02:00.0: eth0: Intel(R) PRO/1000 Network Connection [ 9711.639854] e1000e 0000:02:00.0: eth0: MAC: 3, PHY: 2, PBA No: 005302-003 [ 9712.060770] e1000e 0000:02:00.0: irq 45 for MSI/MSI-X [ 9712.116195] e1000e 0000:02:00.0: irq 45 for MSI/MSI-X [ 9712.117098] ADDRCONF(NETDEV_UP): eth0: link is not ready [ 9712.122684] e1000e: eth0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: RX/TX [ 9712.122693] e1000e 0000:02:00.0: eth0: 10/100 speed: disabling TSO [ 9712.123142] ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready [ 9722.920014] eth0: no IPv6 routers present But, I'm still getting these [ 9982.992851] PCI Status <10> [ 9984.993602] e1000e 0000:02:00.0: eth0: Detected Hardware Unit Hang: [ 9984.993606] TDH <5d> [ 9984.993608] TDT <6b> [ 9984.993611] next_to_use <6b> [ 9984.993613] next_to_clean <5b> [ 9984.993615] buffer_info[next_to_clean]: [ 9984.993617] time_stamp <24da80> [ 9984.993619] next_to_watch <5d> [ 9984.993621] jiffies <24f200> [ 9984.993624] next_to_watch.status <0> [ 9984.993626] MAC Status <80080703> [ 9984.993628] PHY Status <796d> [ 9984.993630] PHY 1000BASE-T Status <4000> [ 9984.993632] PHY Extended Status <3000> [ 9984.993635] PCI Status <10> [ 9986.001047] e1000e 0000:02:00.0: eth0: Reset adapter [ 9986.176202] e1000e: eth0 NIC Link is Up 10 Mbps Full Duplex, Flow Control: RX/TX [ 9986.176211] e1000e 0000:02:00.0: eth0: 10/100 speed: disabling TSO I'm not sure where to start troubleshooting this. Any ideas? Here is the result of ethtool -d eth0 MAC Registers ------------- 0x00000: CTRL (Device control register) 0x18100248 Endian mode (buffers): little Link reset: reset Set link up: 1 Invert Loss-Of-Signal: no Receive flow control: enabled Transmit flow control: enabled VLAN mode: disabled Auto speed detect: disabled Speed select: 1000Mb/s Force speed: no Force duplex: no 0x00008: STATUS (Device status register) 0x80080703 Duplex: full Link up: link config TBI mode: disabled Link speed: 10Mb/s Bus type: PCI Express Port number: 0 0x00100: RCTL (Receive control register) 0x04048002 Receiver: enabled Store bad packets: disabled Unicast promiscuous: disabled Multicast promiscuous: disabled Long packet: disabled Descriptor minimum threshold size: 1/2 Broadcast accept mode: accept VLAN filter: enabled Canonical form indicator: disabled Discard pause frames: filtered Pass MAC control frames: don't pass Receive buffer size: 2048 0x02808: RDLEN (Receive desc length) 0x00001000 0x02810: RDH (Receive desc head) 0x00000001 0x02818: RDT (Receive desc tail) 0x000000F0 0x02820: RDTR (Receive delay timer) 0x00000000 0x00400: TCTL (Transmit ctrl register) 0x3103F0FA Transmitter: enabled Pad short packets: enabled Software XOFF Transmission: disabled Re-transmit on late collision: enabled 0x03808: TDLEN (Transmit desc length) 0x00001000 0x03810: TDH (Transmit desc head) 0x00000000 0x03818: TDT (Transmit desc tail) 0x00000000 0x03820: TIDV (Transmit delay timer) 0x00000008 PHY type: IGP2 and ethtool -c eth0 Coalesce parameters for eth0: Adaptive RX: off TX: off stats-block-usecs: 0 sample-interval: 0 pkt-rate-low: 0 pkt-rate-high: 0 rx-usecs: 3 rx-frames: 0 rx-usecs-irq: 0 rx-frames-irq: 0 tx-usecs: 0 tx-frames: 0 tx-usecs-irq: 0 tx-frames-irq: 0 rx-usecs-low: 0 rx-frame-low: 0 tx-usecs-low: 0 tx-frame-low: 0 rx-usecs-high: 0 rx-frame-high: 0 tx-usecs-high: 0 tx-frame-high: 0 Here is also the lspci -vvv for this controller 02:00.0 Ethernet controller: Intel Corporation 82573L Gigabit Ethernet Controller Subsystem: Lenovo ThinkPad X60s Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B- DisINTx+ Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx- Latency: 0, Cache Line Size: 64 bytes Interrupt: pin A routed to IRQ 45 Region 0: Memory at ee000000 (32-bit, non-prefetchable) [size=128K] Region 2: I/O ports at 2000 [size=32] Capabilities: [c8] Power Management version 2 Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0+,D1-,D2-,D3hot+,D3cold+) Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=1 PME- Capabilities: [d0] MSI: Enable+ Count=1/1 Maskable- 64bit+ Address: 00000000fee0300c Data: 415a Capabilities: [e0] Express (v1) Endpoint, MSI 00 DevCap: MaxPayload 256 bytes, PhantFunc 0, Latency L0s <512ns, L1 <64us ExtTag- AttnBtn- AttnInd- PwrInd- RBE- FLReset- DevCtl: Report errors: Correctable+ Non-Fatal+ Fatal+ Unsupported+ RlxdOrd+ ExtTag- PhantFunc- AuxPwr- NoSnoop+ MaxPayload 128 bytes, MaxReadReq 512 bytes DevSta: CorrErr- UncorrErr- FatalErr- UnsuppReq- AuxPwr+ TransPend- LnkCap: Port #0, Speed 2.5GT/s, Width x1, ASPM L0s L1, Latency L0 <128ns, L1 <64us ClockPM+ Surprise- LLActRep- BwNot- LnkCtl: ASPM Disabled; RCB 64 bytes Disabled- Retrain- CommClk+ ExtSynch- ClockPM+ AutWidDis- BWInt- AutBWInt- LnkSta: Speed 2.5GT/s, Width x1, TrErr- Train- SlotClk+ DLActive- BWMgmt- ABWMgmt- Capabilities: [100 v1] Advanced Error Reporting UESta: DLP- SDES- TLP- FCP- CmpltTO- CmpltAbrt- UnxCmplt- RxOF- MalfTLP- ECRC- UnsupReq+ ACSViol- UEMsk: DLP- SDES- TLP- FCP- CmpltTO- CmpltAbrt- UnxCmplt- RxOF- MalfTLP- ECRC- UnsupReq- ACSViol- UESvrt: DLP+ SDES- TLP- FCP+ CmpltTO- CmpltAbrt- UnxCmplt- RxOF+ MalfTLP+ ECRC- UnsupReq- ACSViol- CESta: RxErr- BadTLP- BadDLLP- Rollover- Timeout- NonFatalErr- CEMsk: RxErr- BadTLP- BadDLLP- Rollover- Timeout- NonFatalErr- AERCap: First Error Pointer: 14, GenCap- CGenEn- ChkCap- ChkEn- Capabilities: [140 v1] Device Serial Number 00-0a-e4-ff-ff-3e-ce-74 Kernel driver in use: e1000e Kernel modules: e1000e I filed a bug on this upstream, still no idea how to get more useful information. Here is a the result of the running that script EEPROM FIX UPDATE $ sudo bash fixeep-82573-dspd.sh eth0 eth0: is a "82573L Gigabit Ethernet Controller" This fixup is applicable to your hardware Your eeprom is up to date, no changes were made Do I still need to do anything? Also here is my EEPROM dump $ sudo ethtool -e eth0 Offset Values ------ ------ 0x0000 00 0a e4 3e ce 74 30 0b b2 ff 51 00 ff ff ff ff 0x0010 53 00 03 02 6b 02 7e 20 aa 17 9a 10 86 80 df 80 0x0020 00 00 00 20 54 7e 00 00 14 00 da 00 04 00 00 27 0x0030 c9 6c 50 31 3e 07 0b 04 8b 29 00 00 00 f0 02 0f 0x0040 08 10 00 00 04 0f ff 7f 01 4d ff ff ff ff ff ff 0x0050 14 00 1d 00 14 00 1d 00 af aa 1e 00 00 00 1d 00 0x0060 00 01 00 40 1f 12 07 40 ff ff ff ff ff ff ff ff 0x0070 ff ff ff ff ff ff ff ff ff ff ff ff ff ff 4a e0 I'd also like to note that I used eth0 every day for years and until recently never had an issue.

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• How to configure networking on an appliance such that it can plug and play on any corporate network?

  - by Joshua Lim

  I had a chance to configure a Moxa NPort device server appliance on my client's network, it was very easy to do so, done in just 2 minutes. Here's what I did:- The Moxa device server had a preset IP address of 192.168.127.254 and subnet mask 255.255.255.0 - http://www.moxa.com/doc/manual/nport/5400/NPort_5400_Series_Users_Manual_v4.pdf Moxa provides a Windows software which I used to "scan" for the device server. It worked like magic! The software returns a list of device servers found. Each device server is identified by MAC address, and by selecting the device server using the software, I can reset the default IP address and subnet mask of that device server! In comparison, during an earlier project, I spent 2 hours trying to get KVM to work for a Windows 7 embedded appliance I'm trying to install in my client's network - http://superuser.com/questions/380305/how-to-configure-windows-7-professional-appliance-pc-on-my-clients-network-usin Prior to that, I have already tried pre-configuring the IP address and subnet mask to the one which my client provided, yet the appliance still can't connect to the client's network! I've also tried cross cable, didn't work either. After KVM worked, I discovered that the network settings were "lost" after I plug the machine into the client's network. Now my question is what can I do to setup my Windows 7 embedded appliance so that it can connect to any network like that the Moxa device server? I tried experimenting this on my network using a Windows machine configured to an IP address of 192.168.127.254 and subnet mask 255.255.255.0, but it doesn't connect to my network that uses 192.168.0.*. :( EDIT: I would like to point out that the Moxa Windows configuration software seems to be able to connect to any Moxa device connected to the network even if it is on a different subnet, as long as the network adapter shows "connected". This is important because the Moxa device has no VGSM port or interface to configure the IP address.

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• Hyper-V networking....still not sure which way to go??

  - by CZhale

  We have our Hyper-V server up and running (Windows 2008 ENT SP2) and started to create some of our VMs. The server has 4 total nics. 2 onboard Broadcom 1gb nic cards and a pci dual port Intel Pro cards 1gb. Right now, I have setup 1 broadcom nic to be the hyper-v host nic, and setup the other broadcom nic for the VMs. We are not using the Intel Nics....should we be thinking about teaming?Link Aggregation?? I just want to achieve the best possible setup for the network, but have read many things for and against teaming the nics?? Thoughts?

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• Basic networking: Centos Server Router + Ubuntu Client setup.. unable to access outside world from client

  - by ale

  I am trying to set up my Centos Server with two NICs as a router. eth0 is connected to the outside world and eth1 is connected to an Ubuntu client. Here's eth0 on the server: DEVICE=eth0 BOOTPROTO=dhcp ONBOOT=yes TYPE=Ethernet eth1 on the server: DEVICE=eth1 BOOTPROTO=static IPADDR=192.168.0.10 # a free address on my network ONBOOT=yes TYPE=Ethernet My server has IPv4 packet forwarding turned on and my iptables only contains: # iptables --table nat --append POSTROUTING --out-interface eth0 -j MASQUERADE # iptables --append FORWARD --in-interface eth1 -j ACCEPT My Ubuntu client has this in its /etc/network/interfaces auto lo iface lo inet loopback iface eth0 inet dhcp gateway 192.168.0.10 but I can't get an Internet connection from the server for my client. I can't even ping my server from the client: $ ping 192.168.0.10 Destination Host Unreachable

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• Networking conflict - What is the most common default computer name?

  - by John

  I recently had to change the name of my computer to log onto a public wi-fi spot, because a computer with my name was already logged on. (I asked a guy there what to do after it said there was already a computer named "Dell(omitted)" logged on.) I've never been at a wifi spot that you had to log into before. I didn't even notice what the computer's name was before. My question is what are the most common default computer names. I'm curious. How often does this sort of problem happen? (I read via Google that Redhat linux default to "localhost" and Toshiba laptops default to "Toshiba.") Somebody probably keeps statistics. (I was referred here from serverfault.com) Thanks

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• Networking Mac OS X 10.6 and Vista via ethernet?

  - by Moshe

  How can I make Vista home premium access OS X hard drive? and the other way around? I'd like to transfer files via direct ethernet. Plugging in an ethernet cable makes both computers recognize a network, but not the other device. Each firewall is turned off, but no luck. Edit: I don't see Windows Sharing in the Service Column.

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• linux networking: how to redirect incoming connections from old server to new server?

  - by aliz

  hi I'm in the process of moving my old server to a new server, but i will keep the old server running for database replication and load balancing, etc. each server has a separate internet connection with a static ip, and they are connected through a local Ethernet connection. I've got Ubuntu 8.04 32-bit running on old server and Debian 6.0 64-bit on new one. shorewall firewall is installed on both servers. there are some outdoor devices which are periodically sending data to port 43597 for old server IP address. I can run multiple instances of the network service which is responsible for receiving data from devices on a server but on different ports. here's the question: how can I run the service on new server and have connections coming to old server redirected to it, and new devices can still connect to new server's IP address preferably on the same port and same service? until all devices get updated to send to new server. I've tried a shorewall DNAT rule, but seems like new server's default route should be changed to ethernet connection, which breaks other things. I also found about redir utility, but still haven't tried it. is there any best practice or simple solution for such a scenario, i'm not aware of? thanks in advance.

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• How do networking ports work? Can I configure the ports that client and server use?

  - by joedotnot

  Let's say i have a "server" program listening on address 1.2.3.4:69 (i.e. remote port 69) When i connect from a "client" program to it, typically i would specify the IP address + port of the target or server system; But what port would the client be using ? And how does the server know which port to connect back to the client on? I understand this question is very general, but just wanting to get a general feel for how things work. Then extending this to a specific protocol, say FTP (typical port 21), can I change it such that the server uses port 69, but the client uses port 100? And similarly, for Remote Desktop in WinXP (typical port 3389), i know how to change the server port to be something other than 3389, but how does one change what port the client uses (if at all possible)?

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• Disable the "disable" option for Networking in Windows Server 2003.

  - by Robin Day

  If you right click the network icon in the system tray in Windows Server 2003, right next to "Status" is "Disable". If you "misclick" this, the result can be catastrophic. Is there a way to disable it, or remove it from the list to avoid "accidently" clicking it?

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• Computer Networks UNISA - Chap 8 &ndash; Wireless Networking

  - by MarkPearl

  After reading this section you should be able to Explain how nodes exchange wireless signals Identify potential obstacles to successful transmission and their repercussions, such as interference and reflection Understand WLAN architecture Specify the characteristics of popular WLAN transmission methods including 802.11 a/b/g/n Install and configure wireless access points and their clients Describe wireless MAN and WAN technologies, including 802.16 and satellite communications The Wireless Spectrum All wireless signals are carried through the air by electromagnetic waves. The wireless spectrum is a continuum of the electromagnetic waves used for data and voice communication. The wireless spectrum falls between 9KHZ and 300 GHZ. Characteristics of Wireless Transmission Antennas Each type of wireless service requires an antenna specifically designed for that service. The service’s specification determine the antenna’s power output, frequency, and radiation pattern. A directional antenna issues wireless signals along a single direction. An omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions The geographical area that an antenna or wireless system can reach is known as its range Signal Propagation LOS (line of sight) uses the least amount of energy and results in the reception of the clearest possible signal. When there is an obstacle in the way, the signal may… pass through the object or be obsrobed by the object or may be subject to reflection, diffraction or scattering. Reflection – waves encounter an object and bounces off it. Diffraction – signal splits into secondary waves when it encounters an obstruction Scattering – is the diffusion or the reflection in multiple different directions of a signal Signal Degradation Fading occurs as a signal hits various objects. Because of fading, the strength of the signal that reaches the receiver is lower than the transmitted signal strength. The further a signal moves from its source, the weaker it gets (this is called attenuation) Signals are also affected by noise – the electromagnetic interference) Interference can distort and weaken a wireless signal in the same way that noise distorts and weakens a wired signal. Frequency Ranges Older wireless devices used the 2.4 GHZ band to send and receive signals. This had 11 communication channels that are unlicensed. Newer wireless devices can also use the 5 GHZ band which has 24 unlicensed bands Narrowband, Broadband, and Spread Spectrum Signals Narrowband – a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies Broadband – uses a relatively wide band of the wireless spectrum and offers higher throughputs than narrowband technologies The use of multiple frequencies to transmit a signal is known as spread-spectrum technology. In other words a signal never stays continuously within one frequency range during its transmission. One specific implementation of spread spectrum is FHSS (frequency hoping spread spectrum). Another type is known as DSS (direct sequence spread spectrum) Fixed vs. Mobile Each type of wireless communication falls into one of two categories Fixed – the location of the transmitted and receiver do not move (results in energy saved because weaker signal strength is possible with directional antennas) Mobile – the location can change WLAN (Wireless LAN) Architecture There are two main types of arrangements Adhoc – data is sent directly between devices – good for small local devices Infrastructure mode – a wireless access point is placed centrally, that all devices connect with 802.11 WLANs The most popular wireless standards used on contemporary LANs are those developed by IEEE’s 802.11 committee. Over the years several distinct standards related to wireless networking have been released. Four of the best known standards are also referred to as Wi-Fi. They are…. 802.11b 802.11a 802.11g 802.11n These four standards share many characteristics. i.e. All 4 use half duplex signalling Follow the same access method Access Method 802.11 standards specify the use of CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to access a shared medium. Using CSMA/CA before a station begins to send data on an 802.11 network, it checks for existing wireless transmissions. If the source node detects no transmission activity on the network, it waits a brief period of time and then sends its transmission. If the source does detect activity, it waits a brief period of time before checking again. The destination node receives the transmission and, after verifying its accuracy, issues an acknowledgement (ACT) packet to the source. If the source receives the ACK it assumes the transmission was successful, – if it does not receive an ACK it assumes the transmission failed and sends it again. Association Two types of scanning… Active – station transmits a special frame, known as a prove, on all available channels within its frequency range. When an access point finds the probe frame, it issues a probe response. Passive – wireless station listens on all channels within its frequency range for a special signal, known as a beacon frame, issued from an access point – the beacon frame contains information necessary to connect to the point. Re-association occurs when a mobile user moves out of one access point’s range and into the range of another. Frames Read page 378 – 381 about frames and specific 802.11 protocols Bluetooth Networks Sony Ericson originally invented the Bluetooth technology in the early 1990s. In 1998 other manufacturers joined Ericsson in the Special Interest Group (SIG) whose aim was to refine and standardize the technology. Bluetooth was designed to be used on small networks composed of personal communications devices. It has become popular wireless technology for communicating among cellular telephones, phone headsets, etc. Wireless WANs and Internet Access Refer to pages 396 – 402 of the textbook for details.

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• XNA Multiplayer Games and Networking

  - by JoshReuben

  ·        XNA communication must by default be lightweight – if you are syncing game state between players from the Game.Update method, you must minimize traffic. That game loop may be firing 60 times a second and player 5 needs to know if his tank has collided with any player 3 and the angle of that gun turret. There are no WCF ServiceContract / DataContract niceties here, but at the same time the XNA networking stack simplifies the details. The payload must be simplistic - just an ordered set of numbers that you would map to meaningful enum values upon deserialization.   Overview ·        XNA allows you to create and join multiplayer game sessions, to manage game state across clients, and to interact with the friends list ·        Dependency on Gamer Services - to receive notifications such as sign-in status changes and game invitations ·        two types of online multiplayer games: system link game sessions (LAN) and LIVE sessions (WAN). ·        Minimum dev requirements: 1 Xbox 360 console + Creators Club membership to test network code - run 1 instance of game on Xbox 360, and 1 on a Windows-based computer   Network Sessions ·        A network session is made up of players in a game + up to 8 arbitrary integer properties describing the session ·        create custom enums – (e.g. GameMode, SkillLevel) as keys in NetworkSessionProperties collection ·        Player state: lobby, in-play   Session Types ·        local session - for split-screen gaming - requires no network traffic. ·        system link session - connects multiple gaming machines over a local subnet. ·        Xbox LIVE multiplayer session - occurs on the Internet. Ranked or unranked   Session Updates ·        NetworkSession class Update method - must be called once per frame. ·        performs the following actions: o   Sends the network packets. o   Changes the session state. o   Raises the managed events for any significant state changes. o   Returns the incoming packet data. ·        synchronize the session à packet-received and state-change events à no threading issues   Session Config ·        Session host - gaming machine that creates the session. XNA handles host migration ·        NetworkSession properties: AllowJoinInProgress , AllowHostMigration ·        NetworkSession groups: AllGamers, LocalGamers, RemoteGamers   Subscribe to NetworkSession events ·        GamerJoined ·        GamerLeft ·        GameStarted ·        GameEnded – use to return to lobby ·        SessionEnded – use to return to title screen   Create a Session session = NetworkSession.Create(         NetworkSessionType.SystemLink,         maximumLocalPlayers,         maximumGamers,         privateGamerSlots,         sessionProperties );   Start a Session if (session.IsHost) {     if (session.IsEveryoneReady)     {        session.StartGame();        foreach (var gamer in SignedInGamer.SignedInGamers)        {             gamer.Presence.PresenceMode =                 GamerPresenceMode.InCombat;   Find a Network Session AvailableNetworkSessionCollection availableSessions = NetworkSession.Find(     NetworkSessionType.SystemLink,       maximumLocalPlayers,     networkSessionProperties); availableSessions.AllowJoinInProgress = true;   Join a Network Session NetworkSession session = NetworkSession.Join(     availableSessions[selectedSessionIndex]);   Sending Network Data var packetWriter = new PacketWriter(); foreach (LocalNetworkGamer gamer in session.LocalGamers) {     // Get the tank associated with this player.     Tank myTank = gamer.Tag as Tank;     // Write the data.     packetWriter.Write(myTank.Position);     packetWriter.Write(myTank.TankRotation);     packetWriter.Write(myTank.TurretRotation);     packetWriter.Write(myTank.IsFiring);     packetWriter.Write(myTank.Health);       // Send it to everyone.     gamer.SendData(packetWriter, SendDataOptions.None);     }   Receiving Network Data foreach (LocalNetworkGamer gamer in session.LocalGamers) {     // Keep reading while packets are available.     while (gamer.IsDataAvailable)     {         NetworkGamer sender;          // Read a single packet.         gamer.ReceiveData(packetReader, out sender);          if (!sender.IsLocal)         {             // Get the tank associated with this packet.             Tank remoteTank = sender.Tag as Tank;              // Read the data and apply it to the tank.             remoteTank.Position = packetReader.ReadVector2();             …   End a Session if (session.AllGamers.Count == 1)         {             session.EndGame();             session.Update();         }   Performance •        Aim to minimize payload, reliable in order messages •        Send Data Options: o   Unreliable, out of order -(SendDataOptions.None) o   Unreliable, in order (SendDataOptions.InOrder) o   Reliable, out of order (SendDataOptions.Reliable) o   Reliable, in order (SendDataOptions.ReliableInOrder) o   Chat data (SendDataOptions.Chat) •        Simulate: NetworkSession.SimulatedLatency , NetworkSession.SimulatedPacketLoss •        Voice support – NetworkGamer properties: HasVoice ,IsTalking , IsMutedByLocalUser

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• Is PHP expertise a requirement for a social networking platform?

  - by brand-newbie

  Is PHP expertise a prerequisite for building a new social networking site? What about Drupal?

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• Home networking - Wireless switch?

  - by gamers2000

  I currently have a Linksys WRT160N that has a couple wireless clients and a few wired clients. We are planning to switch from DSL to cable and unfortunately, there isn't a cable point in a location close to the wired clients (i.e. the new location of the router would be too far from the wired clients to lay Ethernet cables). Thus, I was wondering if there was a wireless switch of some sort in which it would be a standard Ethernet switch that would connect to my wireless network? (This is a home network,of course.)

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• Users not getting ip when connected through wifi,but wired connection getting ip in ddwrt router

  - by Kevin Parker

  I am having DD-WRT v24-sp2(05/08/11) running on Asus RT n 13 u B1 router,with dhcp on. But users not able to connect through wifi...its showing obtaining ip address and disconnects there after. Wired Devices are getting ip address and able to access internet.Wifi was working till yesterday,but all of a sudden it stopped working. on the ddwrt controlpanelsystem information under Wireless Clients mac address of clients that are trying to connect are appearing but soon it disappears. but no such issue with wired clients. Can any one please help me in fixing this..

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• Bridging wireless and wired networks on Linux box

  - by nixnotwin

  I have the following setup: modem + router - - - - -Ubuntu box on master mode.........wireless devises. Ubuntu machine connects to Internet on wired network. I've dhcp3-server, masquerading, and wireless card with master mode on Ubuntu box. The issue is Ubuntu connects to the router on NAT. The wireless devises connect to the Ubuntu box on a NAT too (though different). SO my wireless devises are behind two NAT networks. The solution I am looking for is Ubuntu should forward dhcp requests to the modem+router, and Ubuntu should act as a switch or a bridge that allows wireless devises to connect to the wired network. So the modem+router should act a main router.

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• Playing Age of Empires II multiplayer in VirtualBox Over wi fi network

  - by Gaurav_Java

  I installed Age of Empires II (Expansion) in VirtualBox (hosting Windows XP). It works great in single player mode. Unfortunately, I tried playing multiplayer via WI-FI which I created on my Ubuntu machine and can't seem to join games. But when I connected to my WI-FI router other able to connect to my system and we can play multiplayer mode This is what I've done so far to try to resolve the issue: I noticed that the IP address of my virtual machine was 10.0.x.x, While the local IP on Ubuntu is 192.168.x.x, which I figured was a Problem. So I changed from NAT networking to bridged networking in VirtualBox . I turned off the Windows firewall in the virtual machine and don't have any ports blocked by Ubuntu, so no software firewall should be at fault. However I'm still unable to play multiplayer games, and suspect that some kind of networking issue lies at the heart of the problem. I'm not sure what else I would need to change, however. So essentially I was wondering if anyone else here has managed to play AOE2, or any similar game, inside VirtualBox from Ubuntu, and if so what you needed to do to make it possible. Or if anyone has suggestions on where else to look to figure out the problem, I'd appreciate that as well. Unfortunately AOE2 itself doesn't provide any debugging information to troubleshoot the inability to connect to network games. Here MY IP result both for Ubuntu and Virtualbox XP I want to play game on multiplayer mode in virtualbox on my system(Own Created on Ubuntu ) wi-fi on which other can connect and play hope someone will answer this

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• Is knowledge of hacking mechanisms required for an MMO?

  - by Gabe

  Say I was planning on, in the future (not now! There is alot I need to learn first) looking to participating in a group project that was going to make a massively multiplayer online game (mmo), and my job would be the networking portion. I'm not that familiar with network programming (I've read a very basic book on PHP, MYSQL and I messed around a bit with WAMP). In the course of my studying of PHP and MYSQL, should I look into hacking? Hacking as in port scanning, router hacking, etc. In MMOs people are always trying to cheat, bots and such, but the worst scenario would be having someone hack the databases. This is just my conception of this, I really don't know. I do however understand networking fairly well, like subnetting/ports/IP's (local/global)/etc. In your professional opinion, (If you understand the topic, enlighten me) Should I learn about these things in order to counter the possibility of this happening? Also, out of the things I mentioned (port scanning, router hacking) Is there anything else that pertains to hacking that I should look into? I'm not too familiar with the malicious/Security aspects of Networking. And a note: I'm not some kid trying to learn how to hack. I just want to learn as much as possible before I go to college, and I really need to know if I need to study this or not.

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• Software vs Network Engineer (Salary, Difficulty, Learning, Happiness)

  - by B Z

  What are your thoughts on being a Software Engineer vs a Network Engineer? I've been on the software field for almost 10 years now and although I still have a great deal of fun (and challenges), I am starting to think it could be better on the "other" side. Not to degrade network engineers (i know there are many great ones out there), it seems (in general) their job is easier, the learning curve from average to good is not as steep, job is less stressful and pay is better on average. I think as software developer I could make the switch to networking and still enjoy working with computers and feel productive. I spend an enormous amount of time learning about software, practices, new technologies, new patters, etc...I think I could spend a much smaller amount of time learning about networking and be just as "good". What are your thoughts? EDIT: This is not about making easy money. Networking and Software are closely related, I love computers and programming, but if I can work with both, make more money and have less stress in my life and can spend more time with my family, then I am willing to consider a change and hence I am looking for advice that Do or Don't support this view.

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• Network configuration problem

  - by Musti

  in my dorm I have to change network configuration and then if it is successfull, I have to enter a user name and password for wired internet connection. Anyway, I had many attempts but I couldnt achieve, and please look at my steps and tell me if there is something wrong and at the end there is an error, but I really dont have any idea about this error. (I am a new ubuntu user, and network is far away of my interests) 1) /etc/network/interfaces auto eth0 iface eth0 inet static address 172.030.014.038 netmask 255.255.255.252 network 192.168.2.0 broadcast 192.168.2.255 gateway 172.030.014.038 2) sudo gedit /etc/resolv.conf nameserver 010.050.001.001 nameserver 010.050.001.002 3) /etc/init.d/networking stop Deconfiguring network interfaces... [ OK ] 4) /etc/init.d/networking restart Running /etc/init.d/networking restart is deprecated because it may not enable again some interfaces Reconfiguring network interfaces... 172.030.014.038: Unknown host ifconfig: `--help' gives usage information. Failed to bring up eth0 Note: IP-address, netmask, gateway, Preferred DNS server and Alternate DNS server ara given by the management of Dorm. It wad very easy in windows but I couldnt achieve in Ubuntu. I also tried to edit from "edit connections" but the save button is gray and I cannot save it. Thanks in advance. / Musti

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• Ballooning Mac OS X kernel_task and Wired memory usage. How to diagnose / fix?

  - by user28930

  I have a very strange issue, which I'm having a hard time diagnosing as to the root cause. I have a Mac Pro (2008, 8-core 2.8 GHz, 8800GT) with 14 GB of RAM (recently upgraded because of this issue!). When I boot my system and log in, vm_stat / top / Activity Monitor will show that kernel_task has about 150 MB allocated, and the machine has about 800 MB of Wired memory being allocated. Even initially, 800 MB seems an awful lot of wired memory to be allocated with no applications running - but, it gets worse. (NB: Wired is locked, unswappable memory) After a very short time, sometimes triggered by something as simple as launching a terminal, kernel_task will balloon to 8-900 MB of Real Mem (RSIZE), and Wired Memory will accelerate to 1.6 GB (implying that all the extra memory requests are for wired RAM in the kernel). If I quit everything (I.E: no running applications, bar an activity monitor or terminal to view top), there is no appreciable reduction in either kernel_task RSIZE, or Wired Memory usage. Going the opposite way, and loading the system with tasks also shows that wired memory does not get reduced - and that importantly it is not reduced in preference to heavy swapping. If I log out and log back in again, it reduces a bit (450 MB kernel_task, 1.28 GB Wired), but not back to the start. I'm not running any wacky kexts - and futhermore, kextstat shows no huge memory allocations there; the largest being com.apple.nvidia.nv50hal at about 4 MB of Memory. The machine feels overall more sluggish when this has happened - unsurprisingly because such a huge amount of RAM has been marked as non-pageable. So I have a few questions: 1) Is there a good way to diagnose what has allocated all of this wired memory? It's often over 2 times the kernel_task size, running no applications. The real memory total doesn't seem to add up - it seems that there is a bunch of RAM that isn't being accounted for anywhere. 2) What is happening to cause the kernel to suddenly require 6 times as much memory?

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• 12.04 on VirtualBox -No internet access on Guest OS

  - by Muzab

  I have Windows 7 as my Host OS which has wired Ethernet working. My guest OS on VirtualBox is Ubuntu 12.04. The problem is that I cannot browse. I have: Enabled sharing on Windows; Have used NAT, Bridged Adapter etc ( all possible combinations); With NAT, used PCnet-FAST II (Am79c973) combination. Ubuntu says "connected to wired ethernet1" but I cannot access websites. VirtualBox Host-Only Network in the Network and Sharing center shows that I don't have IPV4 and IPV6 connectivity. Meaning I don't have DHCP configured. Strangely I have DNS address correct in the Ubuntu properties.

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• Hybrid wireless network repeating

  - by Oli

  Summary: I'd like to use two Ubuntu computers to extend/compliment an existing wireless access point. I have a network which currently looks a bit like this: What the diagram doesn't show is the interference caused by our house. It's a wifi-blocking robot sent here from the past. The two wired computers are in areas where the signal is most blocked (not by design, just a happy co-incidence). Both wired computers have fairly good network cards. They're both Ubuntu machines and I would like to turn them into additional base stations. I know I could throw more networking hardware at this (network extenders or cable in additional, pure wireless access points) but I've got two Linux machines sitting in ideal places and I feel like they should be able to help me out. I've tried ad-hoc networks but I need something that is a lot more transparent (eg you can migrate from base to base without a connection dropping); it should look like one network to clients.

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• How to merge multiple internet connections into one

  - by Luis Alvarado

  My PC has 2 wired cards. Both gigalan. It also has 2 wireless cards. One broadcom with proprietary drivers and ralink with open software (which works much better than broadcom). My cellphone can share its connection wirelessly to my PC. But I also have a wired connection. So I have multiple connections that I can use to have internet. How can I merge 2 or more connections together and balance them to enjoy one unified internet experience that it is the sum of all internet connections connected to it. For example if I have an internet connection that offers 1024KB/Sec and another that offers 512KB/Sec and one small one that offers 128KB/Sec, after load balancing and merging all connections, I could download at a speed of 1664KB/Sec using all 3 internet connections as one for example. This question has always intrigued me.

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