Networking refers to the technologies and techniques that enable the interconnection of devices and applications allowing them to communicate electronically.

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Selecting a TCP stream with most bytes transferred in Wireshark

I have captured traffic in Wireshark and I want to follow the TCP stream with most bytes transferred in the traffic. After opening Statistics > Conversations and sorting by Bytes column I filter the ...
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18 views

Inconsistent speed with simultaneous FTP downloads from same server

I have a hosted VPS running CentOS and PureFTPd. When I try to download from multiple FTP accounts on the server simultaneously, I get wildly different speeds for each of the FTP connections: some are ...
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26 views

ATM connection has slow upload speed when connected to switch or router

We just got a new additional ATM line with 10/10 Mbps. When connected directly to a PC NIC, internet speed tests all come up as 10/10 Mbps. However, when connected to any of several routers or ...
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38 views

Setting up Infiniband network - wrong route

So I'm trying to set up an Infiniband network alongside my Ethernet network. I have 10 compute nodes and one conductor node. All 11 machines are running CentOS and are plugged in to an Infiniband ...
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18 views

MAC ID Binding to IP on Windows

Is there a way i can bind a certain IP to have traffic allowed if it has a certain MAC ID on windows routing and remote access or network policies? Basically Associated MAC ID to IP xxx.xxx.xxx.xxx ...
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24 views

Unable to traceroute on Amazon EC2 Ubuntu

I have setup a brandnew Ubuntu 14.04 instance, with a public IP, with a security groups that allows all inbound and outbound traffic using all protocols on all ports from/to any IP. I have installed ...
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1answer
40 views

Remove the unspecified gateway from linux routing table

I've a remote linux machine whose the routing table is : [root@hostname]# route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 ...
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48 views

Windows Server 2008 r2 clients can connect to AD but no Internet. Server connects to Internet fine

I've recently been assigned to manage a network at work. There are two labs (over 40 clients in total) connected to one Windows 2008 r2 server. Roles installed are as follows: Active Directory DNS ...
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2answers
40 views

AWS EC2 : No HTTP Traffic after reboot but SSH is ok

I have a small ami EC2 instance @ AWS. I had to reboot yesterday and after reboot, I couldn't access the websites hosted on the EC2 while there was no problem at all through SSH. Things I checked ...
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33 views

How to efficiently subnet a network [duplicate]

I have base ip address 10.6.0.0/16. I need to divide this network into 12 subnets, and I need at least 80 computers in one network. Please explain how to calculate correctly subnets. I understand that ...
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40 views

What does the @ means in ip link show command?

I am new to Linux network admin. I was learning the ip commands with one of my colleague's server with ip link command. When I try to show to one of the vlan information, I see this: vlan1@eth1: ...
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33 views

How to connect to external server using router from VLAN's

I am newbie. I am trying to build network system in Packet Tracer. Now I have such network layout. I have different VLAN's Accounting and Sales. I have configured this using subinterface in ...
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33 views

How to reverse arp using nping for Windows

I would like to send a reverse ARP to resolve an IP address given a MAC address using nping for Windows. The documentation is not clear on how this should work and I'm unable to find any examples ...
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12 views

VPN Connection from AWS EMR Cluster to Cisco ASA vpn( lan to lan with ipsec)

I have the following problem. I need to connect my AWS emr cluster(in a vpc with a subnet and security groups) to a vpn(lan to lan with ipsec) the one that provides the cisco asa, but i need an ...
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59 views

Ubuntu server 14.04.1 network drop packets e1000e

I'm new with linux OS. We have currently a Ubuntu Server 14.04.1 LTS x64 installed, and it has some network performance problems. This is my ifconfig output p4p1 Link encap:Ethernet HWaddr ...
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67 views

Is it possible to offer failover even using DNS round robin? [closed]

A company X has five ips to a given service. $ host www.example.com.br www.example.com.br has address 13.194.4.159 www.example.com.br has address 13.194.4.152 www.example.com.br has address ...
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33 views

transparent proxy (SSL error)

Right now we are having transparent proxy in our network environment. we have been set proxy settings to browsers in all systems. While accessing the https sites in browsers no issue but few of ...
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4answers
169 views

Communicating via separate network cards

Assume you have a web server with two network cards (and their associated ports), let's call them A and B. The idea is to connect one port (A) to the internet and the other (B) to some isolated ...
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3 views

I cannot reach the website www.github.com [migrated]

Whatever i tried to open github . com in my browser (tried with chrome and firefox), i failed to load web site i can reach every other web addresses except github . com i cannot take projec source ...
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3answers
85 views

KVM guest is unable to access the internet

I have a Debian host that has several allocated IPs and KVM with a Debian guest using a bridged network. The guest is completely unable to reach the network, including the LAN or even the host. ...
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24 views

How do I configure KVM guest to have Internet access?

I am trying to get KVM working on my Debian server and I am having a slight problem with networking with my guest OS (also Debian). The virtual machine is using the "default" network (without a ...
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1answer
38 views

What is “the meaning” of this `ip route`?

I'm slowly learning more about IP routing and the ip toolset by investigating a VPN. After I start a particular VPN client, one of the (new) routes displayed by ip route show is 128.0.0.0/1 via ...
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1answer
41 views

Sending Data extremely slow or RDS

I have the following two profiles for a basic SELECT STATEMENT: select count(*) from mturk_completion; Here are the two profiles: # My Local machine, using a local db Status ...
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3answers
49 views

how to use tcpdump to log only certain data in real time

I'd like to monitor network interfaces but only log things likes errors, collisions and dropped packets. The send that to stdout. – Can tcpdump be configured to do this?
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38 views

Why I cannot access EC2 instance public IP from inside of instance itself?

Here is an example, I have an Linux instance , say, private IP is 10.10.10.10, public IP is 54.54.54.54. Inside the instance, I could successfully ping it's private IP(10.10.10.10) and localhost. ...
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34 views

Linux route cache seems to load outdated settings

On SLES 11 SP3 (Kernel 3.0.101-0.46) I see the following route behavior: When I set a route specific MTU once via ip route change ... mtu lock 1500, everything works as expected (setting an MTU of ...
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61 views

Hop count : Proper way to count hops : Router count vs Router count +1 [closed]

I am very puzzled and confused about the hop-count definition, especially related to RIP metric. Does hop-count have to reflect link count or router count ? Here are two possibilities : Statement A : ...
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42 views

Server 2008 R2 NIC in “Unidentified Network” state after connectivity loss is restored

I am having trouble with 2 servers, both with the same symptoms. When they are reconnected to the switch after losing connectivity, they stay in an "unidentified network" state. Only after cycling the ...
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9 views

How does an L2TP Client know where to forward frame? [migrated]

I'm currently studying about L2TP and there's something I don't quite understand, even after studying a tutorial and some parts of the RFC. Specifically, when connected via L2TP, how does the client ...
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1answer
48 views

Whitebox firewall in datacenter environment

I am looking into alternatives to commercial firewall appliances. Most of the resources available online describe home network firewalls or sub-gigabit networks. Considering than 10GbE is becoming the ...
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2answers
31 views

What would cause ifconfig NIC frame drop counts to increase SLOWLY (90-100 frames per day)?

I have a web appliance running CentOS 5.11. It sees a fair amount of traffic (apologies, I don't have specific numbers but I know it's in use). For some reason, I'm seeing ifconfig error counts ...
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33 views

Work Network 'Freezing' randomly for 20-30 seconds

I have a network of about 15 PC's set up to a switch which is connected to our modem obviously. For some reason, very randomly, while trying to load a webpage (any webpage, not specific) the network ...
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2answers
49 views

The requested operation requires elevation

We have about 15 PCs on our network. I can make changes to all the PCs except one. I keep getting the message "The requested operation requires elevation". When I try to run a program as an admin, ...
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25 views

Snort even though working properly does not report majority of rules

I have installed Snort 2.9.7.0 and it does not detect majority of attacks, such as nmap port scans, downloading exe files, opening documents containing keyword "root". I use Snort together with ...
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2answers
38 views

Inter VM communication in a single Cloud Service

After spending a good amount of time in the Azure documentation. It seems that there is an inconsistency regarding the ability for VMs in the same cloud service (not in a VNet) to talk to each other. ...
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21 views

Enable Netflow plugin in Ntopng

How can I enable the Netflow plugin in the latest Ntopng (1.2.2). There is no 'Plugins' option in the menus or I can't see it. I have logged in the web interface at port 3000 but there is no Plugins ...
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33 views

Why can't I see the Printer? [closed]

I have a Small Network set up as follows: Internet>Modem>Router A     Printer     Workstations Dept A     Router B ...
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1answer
34 views

STP fixes non-looped network. Dumb switches kill network. Can anyone decipher this wireshark readout for me?

Greets long story short we had a power outage here and when the network came back online it would crash out to a flood of ARP requests. This would lead to packet storm/network loop, but after ...
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24 views

Alternative ways to track dropped packets and report output

Instead of tailing /var/log/messages or doing a continuous ping is there a way with ifconfig or ethtool to track dropped packets, collisions, or tx/rx errors in real time?
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34 views

How to find out PID of the process sending packets (generating network traffic)?

Couple of weeks ago I had an issue where I changed DNS addresses in large network of around 300 nodes. After that, some of the nodes still continued to ask old DNS servers, although resolv.conf was ...
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21 views

What are the pros and cons of large receive offload (LRO) vs generic receive offload (GRO)

I have been debugging a scenario where an ESX vmware host is communicating with a virtual linux machine via a virtual switch using TCP/IP. After a congestion event the vmware host is waiting for an ...
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24 views

How to configure 2 NICs on a server

Our office has a server with two NICs. We have two group at our office. Say Group A and B We have two internet connection both connected/plugged in to different switch. Both group need to access ...
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1answer
39 views

routing a second public IP to multiple VM's

myself and a friend have rented a dedicated server and have used KVM and libvirt to create virtual machines for us to use. (we are using debian jessie on the host) we purchased two additional IP ...
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14 views

Mac minis disconnecting from 1GbE: RFI / EMI?

We have several 2012 Mac minis in our server room that reliably disconnect from 1GbE network (but otherwise appear to still be working) when the adjacent servers are under heavy CPU load. We suspect ...
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27 views

My NIC keeps getting the same ip 196.256.x.x [migrated]

I have a strange issue with my network card in my pc. My internal network adapter keeps getting an ip that does not come from the DHCP ADSL router that i have connected it. I have changed cable, i ...
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2answers
35 views

Enabling bridged connections with a single network card with multiple IP addresses

I have a server with one network card in it (eth1). My server is assigned 5 public IP addresses and it is currently configured like this (/etc/network/interfaces): # The primary network interface ...
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3answers
46 views

Mount a drive at login time

I need to mount a drive at login time. I have the home directories in the server, and when a user logs in at a client machine (debian 7), I need to mount his directory temporally at a mount point, ...
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29 views

internet timeout every half hour or so. mutiple vlans affected (all wan access is affected) internal network continues to work

i'm facing a strange issue. our internet is dropping out every 20, 10 or 30 min. it's not exact but sometimes even every 5 minutes. the connection restores usually a minute later. but i'm not able to ...
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35 views

Routing with multiple NICs on debian

I have a machine with two NICs on different network segments, I've set up routing for the different segments. It works if I run all the routing commands manually, but I can't get it to work when ...
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20 views

Port forwarding to different subnet

I have two routers: router A with internet access, and router B acting as wireless access point. Devices are attached to router B via ethernet. I need to forward some ports to PCs attached to router ...