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  • Trying to understand why VLANs need to be created on intermediate switches

    - by Jon Reeves
    I'm currently studying for the Cisco switching exam and having trouble understanding exactly how 802.1q tagging works. Given three daisy chained switches (A,B, and C) with trunk ports between them and VLAN 101 defined on both end switches (A and C), I'm not sure why the VLAN also needs to be defined on the middle one (B)? Note that I am not disputing that it does need to be configured, I'm just trying to understand why exactly. As I understand it, traffic from VLAN 101 on switch A will be tagged as it goes through the trunk to switch B. According to the documentation I have read, trunks will pass all VLANs by default, and the .1q tag is only removed when the frame leaves through an access port on the relevant VLAN. From this I would expect switch B to simply forward the tagged frame unchanged through the trunk to switch C. Can anyone shed some light on how switch B processes this frame and why it does not get forwarded through the other trunk ?

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  • Throughput; capacity planning help for C10K like design

    - by z8000
    I am designing a network service in which clients connect and stay connected -- the model is not far off from IRC less the s2s connections. I could use some help understanding how to do capacity planning, in particular with the system resource costs associated with handling messages from/to clients. There's an article that tried to get 1 million clients connected to the same server [1]. Of course, most of these clients were completely idle in the test. If the clients sent a message every 5 seconds or so the system would surely be brought to its knees. But... How do you do less hand-waving and you know, measure such a breaking point? We're talking about messages being sent by a client over a TCP socket, into the kernel, and read by an application. The data is shuffled around in memory from one buffer to another. Do I need to consider memory throughput ("5 GT/s" [2], etc.)? I'm pretty sure I have the ability to measure the basic memory requirements due to TCP/IP buffers, expected bandwidth, and CPU resources required to process messages. I'm a little dim on what I'm calling "thoughput". Help! Also, does anyone really do this? Or, do most people sort of hand-wave and see what the real world offers, and then react appropriately? [1] http://www.metabrew.com/article/a-million-user-comet-application-with-mochiweb-part-3/ [2] http://en.wikipedia.org/wiki/GT/s

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  • Mac claims to have connected to wireless network, but hasn't

    - by Mick
    I am attempting to connect a new mac OSX 10.6.5 laptop to a wireless network (I am a windows expert but a mac novice). It used to connect without problem to the network when I had the security set to "64 bit wep". Now I have changed the security on my belkin router to "WPA-PSK (no server)". I have two PC's and an old mac connecting via the new security setting without problem. Now I have the problem that on the new mac, the wireless icon is indicating a good connection (5 dark bars). Also the network name has a tick next to it on the wireless drop down menu. But I can not view any websites. I can not even connect to the router by typing 192.168.2.1 into a browser address bar. Any ideas where I went wrong?

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  • How do the routers communicate with each other ?

    - by Berkay
    Let's say that i want make a request a to a web page which is hosted in Europe (i live in USA).My packets only consist the IP address of the web page, first the domain name to ip address transformation is done, then my packets start their journey through to europe. i assume that MAC addresses never used in this situation? are they? First, my packets deal with many routers on way how these routers communicate with each other?, are router addresses added to my packet headers ? Second, is there a specific path router to router comminication or which conditions affect this route? Third to cross the Atlantic Ocean, are cables used or... ?

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  • Extending home network using multiple access point originating from another access point

    - by cyberjar09
    I have a home network with the current setup (RJ45 running from main router to access point) : +-------------+ +--------------+ | 192.168.2.1 | |192.168.2.2 | | router +--------------->access point 1| +-----^-------+ +--------------+ | | +-----+--------+ | 192.168.1.1 | | modem | +-----^--------+ | | | | +--+--+ | ISP | +-----+ However I would like to extend the network to two more floors in the house via the existing Access Point (router is too far and not reachable using a network cable, hence I need to extend using current access point). Please see diagram below : +-------------+ +--------------+ +----------------+ | 192.168.2.1 | |192.168.2.2 | | 192.168.2.3 | | router +--------------->access point 1+----------> access point 2 | +-----^-------+ +--------+-----+ +----------------+ | | | | +-----+--------+ | | 192.168.1.1 | | | modem | | +-----^--------+ | +----------------+ | +----------------> 192.168.2.4 | | | access point 3 | | +----------------+ | +--+--+ | ISP | +-----+ Q1 : is this setup possible? Q2 : if possible, will I have to do anything different from what I did to setup access point 1? edit 1 : I am trying to study the dd-wrt documentation to see which would be the correct mode of operation for me Linking Routers but Im confused because I dont see any info on how to use an existing Access point to extend the signal of the SSID. If anyone could point me to the correct wiki for how I should setup AP2 and AP3 based on AP1, it would be very helpful. For AP1, I did the following Use static IP and setup same SSID as primary wireless router use same security as primary wireless router make AP1 point to 192.168.2.1 (primary router) for DHCP Thanks in advance.

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  • Using 2 Transparent HAProxy for load balancing

    - by Nyxynyx
    We can configure HAProxy to be a transparent proxy by using the guide here, where one of the steps says ...to put the backend servers in a different subnet to the front end clients and make sure that the default gateway points back at the HAProxy load balancer. However when we need to have 2 transparent HAProxy in front of our balanced servers (for redundancy), it seems like this wont work as we can only set one gateway for our balanced servers. What will be the correct way to setup the system such that we can have 2 transparent HAProxy infront of the balanced servers? The main reason for having transparent proxies is the need to find the client's IP addresses over TCP.

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  • how does ospf control flooding?

    - by iamrohitbanga
    what method is used by ospf protocol to prevent looping of flooded packets for link state advertisements? The packet header does not contain any timestamp. How do the routers recognize that it is the same advertisement that they sent before?

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  • Debugging IO limitation

    - by Martin F
    I have a Fedora box with some severe IO limitations which I have no idea how to debug. The server has a Areca Technology Corp. ARC-1130 12-Port PCI-X to SATA RAID Controller with 12 7200 RPM 1.5 TB disks and a Marvell Technology Group Ltd. 88E8050 PCI-E ASF Gigabit Ethernet Controller. uname -a output: 2.6.32.11-99.fc12.x86_64 #1 SMP Mon Apr 5 19:59:38 UTC 2010 x86_64 x86_64 x86_64 GNU/Linux The server is a file server running Nginx with the stub status module enabled, so I can see the current amount of connections. The problem present itself when I have a high number of simultaneous connections in a writing state. Usually around 350, at this very moment it's at 590 and the server is almost unusable and stuck at 230mbit/s. If I run stop and hit 1 to see CPU core usages I have all 4 cores with around 99% io wait, if I run iotop the nginx workers are the only processes producing any read load, currently at around 25MB/s. I have each of the workers bound to their own core. Initially I figured it was just the disks being bugged. But I've run fscheck and smartmontools checks and found no errors. I also ran an iozone test which you can see the result of here: http://www.pastie.org/951667.txt?key=fimcvljulnuqy2dcdxa Additionally, when the amount of connections are low I have no problem getting a good speed. If I wget over the local network it easily hits 60MB/sec. Right now I just tried putting a file in /dev/shm, then I symlinked a file from the public dir to it and used wget over the local network and only got 50KB/s. Also, if I try to cp /dev/shm/test /root/test it quickly copies around 740MB and then slows down HEAVILY. Again with iotop reporting 99% iowait. I'm not really sure how to go about figuring out what the problems are. It could be a natural disk limitation but then the file from /dev/shm ought to transfer so it seems there's a network limit, but that's fine when there's not many connections. Perhaps it's a TCP stack problem but I really have no idea how to check that. Any suggestions on how to proceed with debugging would be very welcome. If additional information is required then let me know and I'll try to get it. Thanks.

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  • what causes drops in apache throughput?

    - by Robbie Mckennie
    i was poking around in the windows task manager, and i found this cool network throughput graphing thing. so i wanted to see it max out, so i started downloading a 1.8gb image (from the localhost to a remote system). but, much to my surprise, it looked like this: i count 16 dips, so i divided the 1.8gb into 16 and i got 115mb. then i looked up the mtu of ip, and i knew the mtu of ethernet from my reading, both far smaller than 115mb. and since tcp is connection orientated, it doesn't have an mtu.

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  • SOHO NETGEAR wireless router disconnects when downloading torrents

    - by Lirik
    I have a NETGEAR WGT624 wireless router at home which dies when there is a heavy torrent load. I open up my torrent client and it downloads for about 5 to 10 minutes and it continues to increase the number of seeds (goes up to 70-80 seeds), but after that the router simply fails and I have to restart it in order to get an internet connection again. When I connect directly via an ethernet cable the router and open up the torrent client, then it seems to be doing fine, but when I go wireless then the router stops working properly (although all the lights are still blinking as normal). Is there any way that I can fix this? New router firmware? Change some router options? Feed it a cookie? Anything?

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  • Access Home Network Server via External Address (DSL vs Cable)

    - by Dominic Barnes
    For the last few months, I've been using a server on my home network for basic backups and hosting some small websites. Up until this past week, I've been using Comcast (cable) as an ISP and now that I've moved into an apartment, I'm using AT&T. (DSL) I've set up dynamic DNS and I can verify it works externally. However, I can't seem to access the public address from within the local network. Is there something DSL does differently from Cable that makes this frustration possible?

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  • Wireless mouse keeps freezing when using whole network bandwidth

    - by Ümit AKKAYA
    Hi i have wireless mouse and keyboard connected to pc with USB receiver. When i downloading something without limiting download speed, mouse and keyboard keep freezing randomly. Mouse : Microsoft Wireless Mouse 5000 Keyboard : Microsoft keyboard 3000 v2 Chipset : Intel HM65 Processor : Intel Core i7 2670QM @ 2200MHz Physical Memory : 8192MB (2 x 4096 DDR3-SDRAM) OS : Win 7 x64 Note : The solution described in http://superuser.com/a/309622/157168 not helped.

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  • Cannot find the "Create Network" menuitem in the WiFi icon menu in Mountain Lion

    - by Chuancong
    I am using Mountain Lion Developer Preview 2. I cannot find the "Create Network" menuitem in the WiFi icon menu in the menubar. It was there before when I was using Lion. It started missing since I upgraded to Mountain Lion Developer Preview 1. By the way, is there any other method to create an ad-hoc WiFi network on OS X? I tried to use Internet Sharing via WiFi, but other devices using the shared connection could not find the Mac in their local networks. I am using an early 2011 MacBook Pro 15'. Thanks.

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  • Connecting a Mac to the office network

    - by user36501
    Hi All, I am busy preparing to start working with a Mac at work - in addition to my old PC. Just wondered, is it difficult to setup the Mac to run on the office network - i.e. does it need any special settings or servers or anything like that? and also printers...can I use the network printer as normal. I am just pottrying to think ahead of any ential issues. Also share drives...will I be able to access share drives and my backups to these shares drives - all a bit daunting! Btw in case you didn't notice I am a Mac Nube lol

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  • I can't connect to my network, except in safe mode

    - by eidylon
    My laptop cannot connect to my network all of a sudden except in safe mode. When it boots, it will show the networks available in the tray popup, but if I click connect on any, it says "Unable to connect" and the troubleshooter is useless. Shortly thereafter all the networks disappear. I have tried removing IPv6 support as I have seen that cause problems. No joy. I've also tried removing the wireless network adapter in Device Manager and reinstalling it, also no joy. I've also tried attaching a USB wireless adapter, and it has the same problem. If I boot in safe mode, then it has no problems at all. Three other devices in the house connect fine, so I am pretty sure it is nothing to do with the router. Any ideas what to check next? I am running Win7 Ultimate on a 2GHz Quadcore with 8GB RAM with a Broadcom 802.11n wireless card. EDIT: RE wired connections: What is very weird is that if i plug in a wired connection, then not only does it connect via the wired connection, but the wireLESS also starts working perfectly. And a soon as I unplug the wire, then the wireLESS stops working again! So it seems the wireless is right now working only in safe-mode, or when a wired connection is also plugged in.

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  • Multiple Set Peer for VPN Failover

    - by Kyle Brandt
    I will have two Cisco routers at Location A serving the same internal networks, and one router in location B. Currently, I have one router in each location with a IPSec site-to-site tunnel connecting them. It looks something like: Location A: crypto map crypto-map-1 1 ipsec-isakmp description Tunnel to Location B set peer 12.12.12.12 set transform-set ESP-3DES-SHA match address internal-ips Location B: crypto map crypto-map-1 1 ipsec-isakmp description Tunnel to Location A set peer 11.11.11.11 set transform-set ESP-3DES-SHA match address internal-ips Can I achieve fail over by simply adding another set peer at location B?: Location A (New secondary Router, configuration on previous router stays the same): crypto map crypto-map-1 1 ipsec-isakmp description Tunnel to Location B set peer 12.12.12.12 set transform-set ESP-3DES-SHA match address internal-ips Location B (Configuration Changed): crypto map crypto-map-1 1 ipsec-isakmp description Tunnel to Location A set peer 11.11.11.11 ! 11.11.11.100 is the ip of the new second router at location A set peer 11.11.11.100 set transform-set ESP-3DES-SHA match address internal-ips Cisco Says: For crypto map entries created with the crypto map map-name seq-num ipsec-isakmp command, you can specify multiple peers by repeating this command. The peer that packets are actually sent to is determined by the last peer that the router heard from (received either traffic or a negotiation request from) for a given data flow. If the attempt fails with the first peer, Internet Key Exchange (IKE) tries the next peer on the crypto map list. But I don't fully understand that in the context of a failover scenerio (One of the routers as Location A blowing up).

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  • Linux static dhcp ip for visitor access internet without requesting MAC address?

    - by ???
    Currently, my company internet access for visitor are required to request MAC address from them if they want to access to internet. Can we do something like the Hotel wifi? they just access to the network and just key in the password, then they are able to access the internet for certain time of period. so far, i have looking for linux solution, but they are no such program/application available. do you all have any experience on it? Regards, MH

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  • Force10 S60 remote management

    - by StaringSkyward
    We've got a Force10 S60 switch to replace an older Cisco. I can't find a way to give the switch itself an IP address on the local VLAN so I can ssh to it. The config guide talks about using either a management interface on a separate management network or dedicating e.g. a gigabit port as a management port with a dedicated IP address. Ideally I would like to do what we do currently with the Cisco switches, which is in effect give the entire switch an IP so it can be reached from any host on the same VLAN without having to use up a physical port on the switch or physically connect the management port to another device. Is this possible with the S60 and if so, how would you give it, say the address 10.0.1.1 in vlan 10 (10.0.1.1/24)? Thanks!!!

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  • How should I isolate computers with different roles on a network

    - by fishhead
    I work in an industrial plant and we have one network(physical wire) that us used for both office usage and for process systems. The office computers are only used for typical office needs but occasionally do connect to the process computers to obtain information from a sql server or for some other purpose. A new initiative is in the works and is rolling down hill from corporate and that is to standardize how the the computers are used at work and they would be severely locked down and only a standard set of applications will be allowed to execute. one of the requirements is to also have non office computers isolated from the company domain. our non-office computers are a mix of Man-Machine interfaces and sql-servers all running software that non standard. My question is, how can we divorce the control systems computers from the company domain but still have access to the servers from the company domain. thanks

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  • How should I isolate computers with different roles on a network

    - by fishhead
    I work in an industrial plant and we have one network(physical wire) that us used for both office usage and for process systems. The office computers are only used for typical office needs but occasionally do connect to the process computers to obtain information from a sql server or for some other purpose. A new initiative is in the works and is rolling down hill from corporate and that is to standardize how the the computers are used at work and they would be severely locked down and only a standard set of applications will be allowed to execute. one of the requirements is to also have non office computers isolated from the company domain. our non-office computers are a mix of Man-Machine interfaces and sql-servers all running software that non standard. My question is, how can we divorce the control systems computers from the company domain but still have access to the servers from the company domain. thanks

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  • How to setup Mac server to use two gateways

    - by Brady
    I recently asked this question: How to set Mac server to use different Gateway for internet bound traffic The answer given works but has presented me with another issue that I didnt make clear in that question. Here is my network layout as it stands: At the moment outside staff members use some services on the existing internet 1 link. Those services are hosted by the Mac server. If I change the gateway of the Mac server to the second modem those outside staff lose visabilty on those services. Now I dont know how to go about solving this issue. I want the second link to be used when the Mac server goes to rsync data offsite but everything else use link one. How do I do this? Thanks Scott EDIT: This has been resolved by setting the default gateway on the Mac server to 192.168.1.254 Thus leaving everything on the network as it was before. but to get the Mac server to use the other link for rsync I've added a route to the Mac server to route traffic to the rsync server through the second gateway. sudo route add -net {server IP's}/{Netmask} 192.168.1.1 I've awarded the answer to gravyface for pointing me to a post on how to make this route persistant in Mac

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  • Free IP address management software

    - by TiFFolk
    We are choosing a system for managing our IP address space. So we are looking for a special free software like IPPlan. So what we have nowadays: Ipplan (Beta IPv6 support) SolarWinds IP address tracker (IPv6 support unknown ) IP module of The NOC Project (BTW, take a look of it, seems to be very promising project) (IPv6 support unknown ) phpIP (Does not support IPv6) IP management from RackTables (Does not support IPv6) Do you know about any other special software, like written above? But: No Wiki No DNS No DHCP No spreadsheet Software should provide: Clear view of available addresses Detail listing of all addresses by subnets/search pattern/owners/additional info It must support adding additional info like owner of IP, domain-name, contacts, etc Multi user support Easy interface Software has to be specially written for address management. Scalability Any OS: win, lin, sol, web

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