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150

Virtual LANs (VLANs) are an abstraction to permit a single physical network to emulate the functionality of multiple parallel physical networks. This is handy because there may be situations where you need the functionality of multiple parallel physical networks but you'd rather not spend the money on buying parallel hardware. I'll be speaking about Ethernet ...


98

I have yet to see a problem with auto-negotiation of network speeds that isn't caused by either (a) a mismatch of manual on one end of the link and auto on the other or (b) a failing component of the link (cable, port, etc). This depends on the admin, but my experience has shown me that if you manually specify the link speeds and duplex settings, than you ...


38

80 MB / second is actually pretty good! That's about 640mbps, which is pretty darn close to the gigabit capacity of the NIC. If you take into consideration the TCPIP overhead, and disk speed you're probably at your maximum speed.


37

For the same reason why the first and second pair are connected to pins 4, 5 and 3, 6: compatibility with telephone systems. In telephony main pair is the middle pair and second pair is the next one from middle (pins 2, 5 in RJ11 and 3, 6 in RJ45). If you're using Fast Ethernet or Ethernet, you can route telephone signal in regular cable and it will work ...


34

The I/O model in Windows is based on a stack of components. Data must flow through the various components of that stack that exists between the physical network card, and the application that will consume the data. Sometimes those various components inspect the data (a TCP packet for example,) as they flow through the stack, and based on the contents of that ...


33

This is an interesting question since I've never seen anything that authoritatively states the design decisions behind that choice. Everything that I've come across, whether on the Interwebs or from conversation with people smarter than me in this area, seem to indicate two possibilities: Future proofing Extra shielding Future Proofing By the time of ...


27

ethtool [interface] last line shows what you want: # ethtool eth0 Settings for eth0: Supported ports: [ TP ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Supports auto-negotiation: Yes Advertised link modes: ...


25

It's at /sys/class/net/eth0/address (or more precisely /sys/devices/pciXXXX:XX/XXXX/net/eth0/address where the XXX is your PCI bus ID, but this varies between systems). (Incidentally, I found this with find /sys -name eth0 and looking at the files in the directories identified.)


25

You are correct that frequencies that high would be completely unmanageable. Sending one bit per frequency would cause problems for various types of radio transmissions as well. So we have modulation techniques which allow more than one bit to be send. A touch of terminology: baud, most people will remember that term from the days of telephone modems, is ...


24

It's just a 110 wiring block. More or less a type of punch down block. (According to a quick Googling, that wiring block is generally Cat5e compliant these days, so you could use it for a 100Mbit network connection). Instead of a patch panel Which has a set number of jacks pre-sized and pre-wired to a certain standard (like RJ45 jacks or RJ 12 jacks or ...


23

Check /sys/class/net/eth0/operstate and other files in this directory As far as I know this is specific to Linux 2.6 but provides a clean interface to the kernel driver.


22

Very common, I've had numerous problems over the years with various types of hardware. In my opinion if the setup is static(i.e. a server rack) and you don't think there will be changes it is a good idea to setup the speeds and duplexs manually. As long as it is well documented so that future problems can be averted. EDIT: Just to clarify, I am not ...


22

The diagram on Wikipedia is horrible. Hopefully what I'm about to write is clearer. The maximum payload in 802.3 ethernet is 1500 bytes. This is the data you're trying to send out over the wire (and what the MTU is referring to). [payload] <- 1500 Bytes The payload is encapsulated in an Ethernet Frame (which adds the Source/Destination MAC, VLAN tag, ...


21

Try putting this to your /etc/sysctl.conf # General 10gigabit/LFP tuning net.core.rmem_max=16777216 net.core.wmem_max=16777216 net.ipv4.tcp_rmem=4096 87380 16777216 net.ipv4.tcp_wmem=4096 65536 16777216 net.ipv4.tcp_syncookies=1 net.ipv4.tcp_max_orphans=1048576 net.ipv4.tcp_orphan_retries=2 # Removes some internal buffering net.ipv4.tcp_low_latency=1 # ...


19

Question is a bit broad but i believe it's still valid for this site. A good initial site survey is very important. Depending on the scale of this, you may need a professional networking company to run the survey for you. I will assume that this has a learning purpose so i'll list what we do when we go to a new site. Disclaimer: a proper network survey is ...


19

You say "WPA2" but I suspect you're not looking for encryption but, rather, authentication. (If you are looking for encryption then skip to the edit at the end of this answer.) I strongly suspect you're looking for is 802.1X authentication. 802.1X allows you to have wired (and wireless) clients authenticate before being granted access to the network. All ...


18

Since mii-tool is deprecated, I'd go for ethtool. Can't you check the other sides opinion of the link speed, btw? mii-tool and ethtool are known to disagree in certain circumstances; you can find bugreports of that on a host of websites. What driver are you using? At least tg3 is known to be a subject of disagreement between the two tools. UPDATE: Checked ...


17

If you're using copper, your cable runs will be limited. (15m for twin-ax, 55m for STP/UTP). Also, bear in mind that you will need Cat6 if you go with the STP/UTP option. (Cat6a will allow you to run 10G/copper at distances of 100m). The other thing you should look into is the relative cost of hardware. Most 10G fiber line cards are modular, with the optics ...


17

ip link show is another. Good old ifconfig dev_name or ifconfig -a will also tell you if the interface is up


17

Perhaps you are looking at this from the wrong direction instead of asking why does DHCP not work maybe you should be asking why does TCP-based communication working on a unreliable network where there is packet loss or corruption. TCP based communication is meant to be reliable and the protocol is designed to retry communication other protocols like UDP ...


17

On an RJ-45 connector, there are 8 pins. Originally only 4 were used. Tx(transmit) and its ground, and Rx(receive) and its ground. If you used a straight through cable, the transmit pins would be connected to the transmit pins on the other device. The same would be true for the receive pins. Early networking gear wasn't "smart" enough to know that data was ...


17

Test the ports thoroughly before trying to use them. I can't speak for your predecessor, but one reason I've seen that done (with cut ends or empty crimped ends) is to "mark" bad or sketchy/lossy ports on a switch; it's a great way to see at a glance that a port should not be used.


17

How does it work? Like this: As Tim pointed out, it takes advantage of the fact that (100Mbit or slower) ethernet connections only use two of the pairs, so one jack can effectively carry two signals. Of course just because it works doesn't mean it's a Good Thing. Given the opportunity you should plan on rewiring your panel (and possibly the rest of ...


16

I use Wireshark on Windows all the time - with a SPAN session or similar, plus cunning use of capture/display filters, you can get it to tell you pretty much anything you need. And you can make pretty graphs for your boss, too. What did you mean by 'security history'?


16

Ethernet is a collection of specifications for layers 1 (PHY) and 2 (DLL).


16

Stop it, you're making me feel old. ;) Ethernet was originally designed to connect to shared media. There used to be devices called "hubs." Outwardly, hubs look almost the same as switches do today, but the way that they forward frames is fundamentally different. Nearly every Ethernet switch will build a database that maps MAC addresses to RJ-45 ports. ...


15

Given an IP address, you should be able to find the MAC address of the corresponding host. arp -a On both Windows and Linux will show you the arp cache of that host, mapping IPs to MAC addresses. (Note that this will need to be run on a machine that is on the same IP subnet as the machine you are trying to find). Once you have the MAC address, log on to ...


15

Networking wire isn't just any old spool of wire. It's rated for the frequencies of the signal going down it (CAT3 for regular phones or 10Mbs Ethernet; CAT5 for 100Mbs Ethernet; CAT5e, CAT6 for 1000Mbs Ethernet), there are pairs of wire twisted in certain ways to reduce the cross-talk between wires, there may be shielding to reduce noise from outside, etc. ...


15

The Physical Coding Sublayer is responsible for delimiting the frames, and sending them up to the MAC layer. In Gigabit Ethernet, for example, the 8B/10B encoding scheme uses a 10 bit codegroup to encode an 8-bit byte. The extra two bits tell whether a byte is control information or data. Control information can be Configuration, Start_of_packet, ...



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