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

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Assigning a public IP to a Xen Guest machine

On my CentOS server (dom0) I have 4 Ip addresses: eth1 - 56.x.x.100 eth1:1 - 56.x.x.101 eth1:2 - 56.x.x.102 eth1:3 - 56.x.x.103 How can I map eth1:1 (etc) to one of my guest machine? Currently ...
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2answers
62 views

What happens when overloading an ethernet cable

As the title suggests, what happens when overloading an ethernet cable? Let's say, I'm using a cat5 cable and transferring 150mbit over it. What will happen? Will it slow down to something below ...
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6 views

Meru wireless access point to controller traffic - packet analysis

We have been having persistent issues with a laptop cart in one of our buildings. The Problem The laptop cart contains (20) Lenovo E531 (i5) laptops running Windows 7 Pro connecting to our greater ...
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1answer
24 views

HP ProLiant DL360 Gen9 - server to server connetion

Just want to know if I can do a server to server connection via Cat6 cable for: HP ProLiant DL360 Gen9 thanks
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16 views

Lost network connectivity after a “yum -y update”

I've a server on Centos 6.5 and after a yum -y update we've lost all connectivity on it, the only access we have is on shell thru SolusVM serial console, I've tried everything (SFTP, SCP) on my reach ...
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17 views

Hosting - actual throughput lower than port speed due to sharing or something else? [on hold]

In the past, when I've transferred very large files between two dedicated servers on 1Gbps ports at two different data centers, I can't actually transfer at 1Gbps unless I use some trick like lftp's ...
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17 views

Windows 2012 Server r2 dont let me install a Custom Service

I need install a custom service on Microsoft Windows 2012 r2 64-bits, but the system says "it's all ready install" (when I try to install it) or "service not found" (when I try to uninstall). What ...
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16 views

Diagnosing a 2-minute delay in HTTP GET request

Under narrow circumstances, I get a 100% reproducible delay of approximately 2 minutes when I request a public web page. The page in question: https://id.openjdk.java.net/console/login Splicing ...
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1answer
20 views

multi-master databases in low connectivity environments

I'm working on a project that has many client devices distributed in remote environments where connectivity losses are frequent and expected. Clients continue to operate when offline, but when these ...
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2answers
39 views

Server talks to one group but not other, both groups talk to each other

I've been trying to figure this out for a couple of days now and no luck so I thought I'd ask here. We have two buildings connected via a line of sight wireless network bridge. We have two routers, ...
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21 views

Why some iptables DNAT rules stop working after some times until reboot?

After a while some of my iptables DNAT rules stop working. If I reboot my server, all of the rules work back. Desciption of the architecture : Tens of hosts (senders) send some UDP packets (one-way ...
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1answer
13 views

Changing Azure VM networking settings

This is probably a stupid question but I am going to ask anyway. I have a VM running on Azure. I go into network connections and change the IP and gateway and I loose connection. What options do I ...
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19 views

How to correctly setup multiple IP addresses pointing to one instance in EC2?

I currently have one ec2 instance which I'd like to have 2 public IPs pointing to. I have 2 EIPs allocated, 2 network interfaces to which the EIPs are attached and which are both attached to the ...
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0answers
11 views

Virtualbox internet through browser login issue [migrated]

I'm working on a Windows host machine that has internet through an Ethernet cable after which I need to do a login through a webportal (it's Kotnet). Previously, when working with a bunch of Linux ...
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19 views

iptables ipset misconfiguration?

I'm looking for a solid method to block unwanted TCP/IP traffic. On my linux machine iptables and ipset seem to offer a nice way to do so. Until now I've done this: ipset create ipsok hash:net ...
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1answer
12 views

dhclient.conf missed on centos

on centos 6 I need take the values from a dhcp server: cat /etc/sysconfig/network-scripts/ifcfg-eth0 DEVICE=eth0 HWADDR=00:50:56:27:0E:C8 TYPE=Ethernet UUID=20924b21-e92a-4944-a054-06d1967155c1 ...
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1answer
26 views

how to connect 2 networks with different routers

I have a TP-Link TL-ER6120 VPN router and a Cisco RV-180 VPN router. I want to have 2 networks with two routers connecting each other. My network is the following: Internet -----> TL-ER6120 ...
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2answers
32 views

Is there a way to query all the mac addresses in a network?

I know this question was flagged "off-topic" and "non-professional", but when creating a gateway or IDS, this might be quite relevant. Also, Google finds nothing usable... There is a thing called ...
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1answer
15 views

Clients connected to “vlan hub” can't access internet on dedicated, natted vlan

I'm trying to get my network up and running with my new provider's vdsl router, which can't operate in "modem-mode" or "bridge-mode". My setup so far is as follows: I have two managed switches, ...
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1answer
28 views

How to tell what is blocking internet (download) on cloud server

Background: My employer is using a cloud-based database server through a service called Rackspace. This server is accessed by our other servers via ssh. Our network admins are unreachable for the next ...
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0answers
15 views

Windows Server spamming devices on other subnets on port 445

I have a Windows Server 2012 that every few seconds sends packets destined for port 445 on local IPs on other subnets. The IPs on other subnets it is trying to reach are devices such as VoIP phones, ...
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1answer
49 views

How do I test my internet connection speed via a Microsoft Windows Terminal?

I currently have two production servers. One running Windows Server 2003 and the other Windows Server 2008. When I open the Reliability and Performance Monitor I see a Network section that only goes ...
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32 views

Debian does not shut down interface with ip link set … down

I have a really specific question for a trunk-testing environment. I have this network setup: +------------+ +------------+ | | +-----+ | | | eth0 ...
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18 views

No connection available in pool. netstat RecvQ shows high number

In our servers there is one particular dependency (java jar), which makes a total of 1024 connection to various remote servers (the library works as a service discovery). Intermittently, it is ...
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1answer
16 views

Qemu Proxmox VM - Network access to guests for BackupPC backups

Environment I rent a dedicated server from OVH and installed Proxmox 3.3 (which is based on Debian 6 Wheezy) in order to create and manage multiple Virtual Machines on it. Each VM is configured to ...
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1 Manage switch & all other unmanage switches in LAN! Message flood? [on hold]

I have 1 PC which works as server & 99 Hardware devices(custom PCB) which can use Ethernet. Right now I use 1 Manage switch as master switch which connect between PC & all others. Each board ...
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1answer
19 views

Map ports from 2 switches to simulate a straight through physical link [on hold]

Is it possible configure 2 brocade ISX 6430 switches connected together to directly map a port on switch 1 to another port on switch 2 so that whatever is plugged into the port is treated the same as ...
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1answer
34 views
+100

Sync server China / Out of China

I am currently managing the backend server of an Android Application. We use DigitalOcean in Singapore, that we thought was a good location for China too. Unfortunately, testing the response time from ...
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1answer
44 views

How to setup 3 networks on a 2 NICs Ubuntu box?

I need to configure 3 networks on my Ubuntu machine (OpenStack Network node) The /etc/network/interfaces I have is: # interfaces(5) file used by ifup(8) and ifdown(8) auto lo iface lo inet ...
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16 views

Make local server available to other computers in the local network [on hold]

I'm running VirtualBox on Windows 7, the VM OS is Ubuntu Server and it's set up in such a way that I can access it from the host machine on 192.168.56.101. The host machine IP in the local network is ...
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1answer
50 views

Route between local machine and a VM running on remote server

I'm trying to establish a route between my local machine (LM) and a VirtualBox VM (VM, create with Vagrant and configured with Host-only Networking) running on a remote server (RS). The setup is as ...
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How to filter for the most common problems with tcpdump/tshark

I am currently using the following command in Linux to get specifics on network problems. tshark -r file.pcap -q -z io,stat,1,\ "COUNT(tcp.analysis.retransmission) tcp.analysis.retransmission",\ ...
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IPSec bandwidth between two Pfsense hosts has predictable, variable bandwidth

I have a IPSec tunnel between two Pfsense machines. Both machines are connected to a 100mbps symmetrical connection. The latency between the two routers is ~70ms. I'm using AES-GCM-128 and SHA1, both ...
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1answer
54 views

Is it the normal behavior of arp requests?

Sometimes I dive into my network and often I see: tcpdump -n arp 17:59:15.754508 ARP, Request who-has 192.168.1.65 tell 192.168.1.212, length 28 17:59:16.754401 ARP, Request who-has 192.168.1.65 ...
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Network Interfaces Cards and rx_short_length_errors and Linux Kernel

My machine (Linux OS) is counting packets with wrong length, it is a huge environment (GW's, Routers, Switches...) , so I would like to understand how NIC's behaving with these packets. -Does NIC's ...
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1answer
41 views

Wake-on-LAN: Unicast is not working. Why?

I am facing a strange problem while setting up wake-on-LAN in our company network. The following is true for the workstation to be waked-up: WOL is enabled in the BIOS and in the settings of the ...
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IPV6 at home: my ISP delegates me a static IPV6 /56 subnet, how can I set up an IP scheme & DHCP6 for my network? [migrated]

My network looks like this: (Cable Modem/Router) <-> (PfSense Router) <-> (Internal Hosts) The IP (changed for security) of my cable modem is: IPv6 Address ...
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node.js on ubuntu 14.04 not responding to WAN requests

I've been working with node.js building a simple app that serves up some data in JSON, and decided to try setting up a proper server. I put Ubuntu Server 14.04 (32bit) on an old computer, along with ...
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1answer
78 views

firewalld vs iptables - when to use which [on hold]

TL;DR On new CentOS server installs should I be using firewalld or just disable that and go back to using /etc/sysconfig/iptables ? firewalld and iptables serve similar purposes. Both do packet ...
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2answers
29 views

Installed a new Sonicwall at MPLS provider's DC, got it working by luck but have no idea WHY it's working like this

I'm nervous leaving the device like this because it makes no sense to me WHY it's working like this. We put in the new Sonicwall to replace an older Cisco ASA. Just did the basic setup, using same ...
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0answers
18 views

No connectivity between azure VMs

In my azure environment, I have 4 VMsx running Windows Server 2012 R2 10.0.0.4 (AD, DNS) 10.0.0.5 (ADFS) 10.0.0.6 (MSSQLSERVER) 10.0.0.7 (IIS) All of the machines are connected by an azure virtual ...
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42 views

Lan to internet IPv6 [on hold]

I have 2 iface Lan and Internet with only One IPv6. Over my lan I have a DHCP and DNS server ready for IPv6 support (I use DNSMasq). I'm On OpenVz CT but i can play with kernel module. I use ...
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1answer
32 views

Need advices on iptables

Helly guys ! :-) . I need a (several?) advice(s) from you about my iptables setup. I'm pretty new to iptables, and this is the first time I configure a server with iptables ONLY as a firewall (we ...
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1answer
16 views

Access Point config through static IP [on hold]

My school have LAN cable for every dorm room, Computer want to access to inter net must set static IP and DNS. Mine as follow: IP: 10.107.31.99 Sub: 255.255.255.0 Gateway: 10.107.30.1 DNS: ...
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1answer
55 views

snort: drop icmp rule doesn't actually drop packets

I installed snort-2.9.7 from sources, and launch as IDS: % snort -devQ -A console -c /etc/snort/snort.conf -i eth0:eth1 Enabling inline operation Running in IDS mode ... The config file is very ...
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1answer
38 views

How to remove crypto-ransomware on my network domain

Today some computer on my domain got infected with crypto-ransomware and have infected some folders on file server that only some computers on network have access to. So I presume one or more of five ...
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VLAN configuration on HP J9279A

I've tried to set up separate VLAN for lab environment on one of my HP switches (J9279A/J9280A). Network schema: WAN | GW | ...
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1answer
30 views

Watchguard Mobile VPN with SSL - user can't connect - failed to open shared memory for openvpn command (error: 2)

I have a problem with my Watchguard VPN. I've set up the device for SSLVPN (added policies, users, a group etc.) according to this description from the Watchguard docs. The authentication itself ...
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0answers
25 views

Persistent error when installing windows server essentials in windows server 2012

I'm getting an error when trying to perform post installation configuration of windows server essentials in windows server 2012: An error occurred when installing Windows server essentials. Please try ...
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1answer
21 views

What exactly happens to packets written to a TUN/TAP device?

I'm trying to send packets to an application listening on eth0 from machine's user-space as if they were coming from a remote machine. What I can't seem to find good documentation for is the exact ...