Linux Networking refers to any networking function performed by a server running Linux. A Linux server operating as a router or firewall are the most common applications.

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1answer
79 views

bad localhost resolution on linux [closed]

$ dig @127.0.0.1 localhost $ dig @127.0.0.1 localhost. ;localhost. IN A ;; ANSWER SECTION: localhost. 604800 IN A 127.0.0.1 ;; AUTHORITY SECTION: localhost. 604800 IN NS ...
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1answer
50 views

Why are ICMP packets not captured on the target interface?

I have a network setup as in the picture: The central box is a gateway (Ubuntu 15.10) which relays the packets betwen the various networks (only one is shown on the picture - lan0) and Internet. ...
1
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0answers
31 views

iperf actual send rate always lower than the expected target bandwidth until some equilibrium reached. Why?

I did an UDP iperf 2.0.5-Ubuntu test between two VMs on the same hypervisor. As can be seen in the iperf output below I started my first test with "-b 686M" flag. However, iperf reported that it was ...
1
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0answers
42 views

CentOS 7 ifup scripts actually doesn't change interface name

It has occurred to me that in CentOS7. While one can still specify interface names in sysconfig, the ifup scripts actually does not change interface fact "via ip link set dev ${DEVICE} name". For ...
0
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1answer
52 views

iptables counters in NAT table and state NOT NEW

I read everywhere that it is dangerous to do traffic filtering in the nat table because the nat table is only consulted for connections whose state is "NEW" (later packets bypass the table). Does it ...
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0answers
50 views

iptables (nth) load balance, connect failed: Connection refused when many request

I try to use iptables as load-balancer using round robin scheduling. Block Diagram My itables configuration on 172.18.3.190 like this : *nat :PREROUTING ACCEPT [42:7044] :INPUT ACCEPT [26:4290] :...
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0answers
41 views

What rules do i need to allow ipsec in iptables firewall?

I have a server sitting on a private subnet behind a iptables firewall. On that server I am planning to create site to site VPN to Amazon VPN. I am not sure what rules do I need to put in my iptables ...
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1answer
99 views

How to block all domains except few in BIND DNS?

I came across solutions for blocking selected DNS resolutions by creating block zones. But how would I allow certain sites only and blocking all others in BIND?
1
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1answer
102 views

Cannot access Debian smb share from Windows 7 64

This is an old problem, an in my experience the connection between windows and samba is unstable and different for every implementation. Sometimes it works, sometimes it doesn't, often without any ...
6
votes
2answers
307 views

Accelerating VPN speed using multiple connections

I have set up a VPS with openVPN running on centOS. The VPN works, but it's too slow. Is there a way to speed this up using open multiple connections like IDM or aria2? I'm using openVPN but I'm ...
1
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1answer
44 views

Compare two Linux servers for network configurations [closed]

Some guys did initial setup of servers and they moved on now we see lot of network issues on new servers I want to find a way to compare servers ( New vs old ) to check any specific tuning which was ...
0
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0answers
70 views

Firewalld blocking Squid

I have a serious problem here with Squid and Firewalld in Fedora 23. When I activate firewalld, I can not access the proxy I created, it returns a "Connection refused by the proxy server", but when I ...
0
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1answer
74 views

QOS with iptables and tc with unstable WAN

I have a router/gateway under Linux, I want to add some QoS to reserve bandwidth for a specific flow. This can be done with iptables/netfilter and tc, but all examples start from the fact that you ...
0
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2answers
40 views

Binding conflict with iptables rules [closed]

I m developing a server in C which bind on a random port I m afraid that the choosen random port could conflict with iptables rules. I mean if the choosen port could be already exist in iptables as a ...
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votes
2answers
95 views

Multiple NIC same subnet [closed]

I have a setup as shown in the image. I know it is insane but i have to work on this configuration only. It is basically an ubuntu server acting as a router with 4 interfaces. 3 of them (eth0, eth1 ...
1
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0answers
70 views

Using LINK_REQUIRED parameter with wicked

I'm running SLES 12 and trying to configure network interfaces; this is my first experience with wicked. I'm using "ifup" to up the ethernet devices. I ran into an issue of not being able to ifup the ...
0
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0answers
18 views

Add second openvpn server for one segment subnet with able to see each to each of clients?

There is openvpn server for one segment subnet, client to client visibly, and static assign private IP addresses. But this server may be is off. How add second server for solve minimum time off ...
0
votes
1answer
28 views

Remotely remove MAC table entry from Juniper router

In our colocation we have multiple linux servers with a public uplink connected to a juniper MX40 (that we can not control) and an internal link each. Sometimes we get incoming UDP flooding ...
0
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0answers
80 views

Added OVS bridge in /etc/network/interfaces and then rebooting made Ubuntu machine lose its connectivity

I am trying to define an OVS bridge br0 in /etc/network/interfaces file(ubuntu 14.04). The /etc/network/interfaces file is as shown below: auto breth0 allow-ovs breth0 iface breth0 inet static ...
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1answer
261 views

Setting up DNS server to resolve request to domain “abc.com” to its own host

I have a server with the public ip-address (lets say) 198.20.30.40 I am trying to setup a DNS server on this host so that I can resolve all request to "stackoverflow.com" being made to get resolved ...
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0answers
53 views

How to set multiple client IPs on a single machine mapped to multiple public IPs on a single OpenVPN server?

I have a properly working setup of an OpenVPN server in which: Each client has its own VPN IP address Each client IP is tied to a public IP Client configs are separated by CCDs So far, a client is ...
0
votes
3answers
84 views

Assigning multiple IPs to the same machine with one interface

I have a server with a single physical interface eth0. I intend on running VMs on this server. To that end I have an IPv4 block which is routed to said server. What I'm trying to achieve is to spin-up ...
0
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0answers
49 views

arpwatch to listen only to particular network

I deploy arpwatch is our network and it is working fine. But it is not doing exactly what i need. Here is what i need ... i want it to listen to one particular network ... for example on ethernet 0 it ...
1
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1answer
175 views

Can't connect to remote centos 7 install from at least one host

Edit: It would appear that the problem has somehow magically disappeared after leaving everything alone for almost 24 hours. After just sitting down to look into it further, I notice that my website ...
1
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0answers
63 views

IP Multicast between Windows and Linux

Our team is developing linux/windows applications for our network that are talking to each other via multicast. We had it working when we only had linux boxes on the network, but we recently added a ...
0
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0answers
26 views

Can not connect to ssh over IPsec VPN

I am trying to reach a machine via an ike IPsec (shrew soft) VPN connection. I can ping the remote machine: $ ping 10.3.6.10 PING 10.3.6.10 (10.3.6.10) 56(84) bytes of data. 64 bytes from 10.3.6.10: ...
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0answers
59 views

What happens when connecting to port in TIME_WAIT state?

I'm trying to understand the effect of TIME_WAIT on subsequent TCP connections. I understand how TIME_WAIT behaves when net.ipv4.tcp_tw_reuse = 1, as explained by this answer. But what happens when ...
0
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0answers
39 views

IP Tables, does it really need those rules?

I am just starting with IPTables, and I am wondering if I really have to create so many rules for a simple setup: DMZ (Reverse Proxy) port 80 + 443 Frontend Subnet: Apache Webserver The Reverse ...
0
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0answers
57 views

TCP sockets dying on LTE

I have about 25 audio streaming clients built on an i.mx6 arm platform, running linux version 4.3.0-rc2-00019-gbcee19f-dirty #36 SMP Tue Feb 9 15:27:51 EST 2016 armv7l I find on two specific units ...
1
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0answers
29 views

IP Aliassing - Multiple Public IP Address [closed]

I have a problem with IP Aliassing. I want that all IP addresses have ism traffic but it does not work except to redirect eth0 with iptables DNAT and SNAT which is ineffective. auto lo iface lo inet ...
1
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0answers
38 views

rx_queue value in /proc/net/udp grows to twice the SO_RCVBUF value

When using an SO_RCVBUF of 10485760 (which is also the current limit as stipulated by sysctl's net.core.rmem_max setting, and sending UDP packets faster than the receiving side is able to handle, the ...
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0answers
27 views

tcp receive buffer size min value seems not work

I tried to increase tcp min receive buffer size to 87380, so in my test it would OOM quickly with a little connections. net.ipv4.tcp_rmem = 87380 87380 6291456 net.ipv4.tcp_wmem = 87380 87380 ...
1
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0answers
96 views

How to prevent persistent naming of network interfaces, like eth1

I have a freshly installed Debian Jessie. I had two NICs, which were eth0 and eth1, now I took out one, however I still have eth1 left in the system: % dmesg ... tg3 0000:03:00.0 eth0: Tigon3 [partno(...
1
vote
1answer
128 views

Use tcpdump to capture an ICMP destination unreachable message

I am new in this area. I am asked to use tcpdump to capture an ICMP destination unreachable message in my network course. So I am trying to capture one message that is an ICMP destination unreachable ...
1
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2answers
219 views

Trouble getting transparent Squid forwarding proxy working with ssl

I have an environment consisting of four servers networked together. One server acts as the server, and the other three act as clients for running automated tests and Linux benchmarking using ...
1
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0answers
68 views

Change NAT IP for Proxmox (Keep host IP)

I have a Proxmox server with many IPv4 addresses available to it. As it stands, an instance (Either LXC or KVM) that connects out to the Internet will be connecting from the host's IP address. For ...
0
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0answers
139 views

Force isc-dhcpd to disregard client hostname in ddns updates

I have the following configuration of isc-dhcpd-4.3.1: ignore client-updates; ddns-update-style interim; subnet 192.168.128.0 netmask 255.255.255.0 { use-host-decl-names on; update-static-...
0
votes
1answer
67 views

AWS port unreachable on REHL

I know there are tons of posts about not being able to connect to an AWS ec2 instance, but this is not quite the same. It is similar to What causes the 'Connection Refused' message? but that ...
0
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0answers
74 views

How does the captive portal redirect work behind the scenes

As a project I am building my own captive portal web pages for "unauthenticated" users. Those are users that have not hit a button on my captive portal page. I want this to be out of band (like a ...
1
vote
3answers
109 views

Forward all traffic when connected to a hub

I have a Ubuntu with two NICs. eth0 is connected to a hub and eth1 is connected to Internet. eth1 is used to do a point to point VPN using openVPN. So I have a tun0 interface. the VPN tunnel endpoints ...
0
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1answer
72 views

How to create virtual networks by using libvirt?

I have installed qemu/kvm and have tried to create some virtual machines and network them together. What I would like to achieve is 2-3 virtual machines in their own private network (e.g. 10.0.0.0/24)...
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votes
1answer
135 views

Default gateway and ARP confusion

I have the following configuration (I'd post a pic but not enough rep for more than 2): PC1 (10.0.2.10/24) and PC2 (10.0.2.137/29) are connected to a hub, which is connected to a router on interface ...
0
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0answers
161 views

what is the “ip route” equivalent of “route add -host” in linux?

Specifically, route add -host allows me to specify the host via hostname to add a route to a host, e.g., route add -host www.google.com gw 192.168.1.1 However, I cannot find a way to do this using ...
0
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0answers
19 views

Add new subnets to KVM Host

I need to assign a handful of /27 subnets to my KVM host node (Centos 6). I routed them correctly at the Cisco switch, so that's all go. Traceroute & ping works fine on gateway on each subnet, ...
3
votes
1answer
63 views

Find network percentage of NIC [closed]

So I have created a Linux resource monitoring tool that pulls various resource information. One of the fields I am trying to pull is the percent of network throughput on my NIC. So if I have a 1 Gb(...
2
votes
0answers
30 views

network access issue and triage

We have two hosts in same vlan with same route rules. One of them is able to connect to an outside IP while on another I get failed: Connection timed out when testing the connectivity through netcat. ...
1
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0answers
50 views

iptables/nat/prerouting ignores UDP packets?

The same effect on many servers with various kernel versions. There are multiple Iptables DNAT rules: iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 12345 -j DNAT --to-destination 10.20.30....
3
votes
1answer
426 views

How to properly permanent enable ip forwarding in Linux with systemd?

I try to enable ip forwarding (between enp0s3 and tun0 interfaces) and write net.ipv4.ip_forward = 1 in /etc/sysctl.conf. After restart I have $ cat /proc/sys/net/ipv4/ip_forward 1 But forwarding ...
0
votes
1answer
29 views

How do I properly configure KVM

I have a remote dedicated server on which I have installed KVM. When trying to create my first virtual machine I am unable to ssh to the machine. I assumed that I needed another ip address so I ...
1
vote
1answer
29 views

Routing via sub-interfaces not working?

I'm trying to isolate outbound network traffic to a specific target for metering purposes, so I thought I'd route it via a dedicated IP address. In order to achieve this I have setup a subinterface ...