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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23
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8answers
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how to find out mac addresses of all machines on network

Is there some easy way to find out mac address of all machines on my network rather than doing an SSH into each and ifconfig | grep HWaddr if there are 300 machines on network I really need some easy ...
22
votes
2answers
30k views

How to reduce number of sockets in TIME_WAIT?

Ubuntu Server 10.04.1 x86 I've got a machine with a FCGI HTTP service behind nginx, that serves a lot of small HTTP requests to a lot of different clients. (About 230 requests per second in the peak ...
21
votes
5answers
7k views

Hostnames - What are they all about?

I've recently been "forced" to perform some sysadmin work, while this isn't something that I absolutely love doing I've been reading, experimenting and learning a lot. There is one fundamental aspect ...
17
votes
5answers
6k views

What network loads require NIC polling vs interrupts?

Does anyone have some data or basic calculations that can answer when frame coalescing (NAPI) is required and when a single interrupt per frame is sufficient? My hardware: IBM BladeServer HS22, ...
15
votes
2answers
1k views

Serving 10,000 simultaneous users over Wifi

I'm looking to offer a wifi service at a public event. The traffic will be very minimal, 10KBps should be adequate. Users don't necessarily need to connect to anything other than the private intranet. ...
12
votes
2answers
2k views

arp-requests cannot be seen by specific nodes

I create an open ad-hoc wlan by using iwconfig (I have the same issue with wpa_supplicant as well). there are 4 nodes on the network as seen on the figure below. The nodes run ubuntu 12.04 and debian ...
11
votes
2answers
5k views

PXE Booting Virtualbox guests in internal networking mode?

I am not sure if this is just specific to my distro's packages or is a vbox limitation. So, any help would be appreciated. Ok, so I have a network of VMs, with one VM acting as a NAT for the other ...
10
votes
2answers
29k views

Linux e1000e (Intel networking driver) problems galore, where do I start?

I'm currently having a major problem with e1000e (not working at all) in Ubuntu Maverick (1.0.2-k4), after resume I'm getting a lot of stuff in dmesg: [ 9085.820197] e1000e 0000:02:00.0: PCI INT A ...
10
votes
4answers
16k views

multiple MAC addresses on one physical network interface (linux)

Simple question: How can I setup multiple MAC addresses on one physical network interface (linux)? Why? My ISP is checking ip<->mac on GW and I d like to route traffic through my "linuxbox" and ...
10
votes
2answers
8k views

How to generate netflow data in linux

We have a number of Linux servers for which I would like to capture netflow data to be processed by a netflow analyzer. I've been spoiled by the ease in which Mikrotik routers allow netflow data ...
10
votes
6answers
19k views

Delete a iptables chain with its all rules

I have a chain appended with many rules like: > :i_XXXXX_i - [0:0] > -A INPUT -s 282.202.203.83/32 -j i_XXXXX_i > -A INPUT -s 222.202.62.253/32 -j i_XXXXX_i > -A INPUT -s ...
10
votes
1answer
2k views

Should /etc/hosts contain an entry like '127.0.0.1 localhost myhost.example.org myhost'?

When looking at a variety of Linux and FreeBSD systems, I've noticed that on some systems /etc/hosts contains an entry for the public hostname of the host, but not on other systemst. What is the best ...
10
votes
4answers
2k views

tc u32 — how to match L2 protocols in recent kernels?

I have a nice shaper, with hashed filtering, built at a linux bridge. In short, br0 connects external and internal physical interfaces, VLAN tagged packets are bridged "transparently" (I mean, no VLAN ...
9
votes
3answers
347 views

Any free networking lab?

I want to study network. But I don't have an access to a sample network (routers, DNS, IP4, IP6 windows linux mixed heterogenous system). Do you know any online network to study (Free as possible). Is ...
8
votes
2answers
3k views

Can I have dots in a hostname?

I'm using names like a.alpha for the hostname of my linux box, but it seams that these name are not completely usable. The response of a hostname shell command is correct (a.alpha). But the name ...
8
votes
1answer
18k views

What CAN cause 'RTNETLINK answers : No such process' when adding a route

I have come up against this error a number of times, but haven't yet found an explanation of what the error means, or what can cause the problem. I'm not posting my configs or the specific route I'm ...
8
votes
2answers
9k views

How can I increase the value of somaxconn?

I can check its value by cat /proc/sys/net/core/somaxconn, is it OK if I change it simply by echo 1024 > /proc/sys/net/core/somaxconn?
8
votes
1answer
31k views

What does “net_ratelimit: 44 callbacks suppressed” mean on a linux based router?

I'm trying to tune Snort performance on a Debian based router. I was seeing stuff like: snort packet recv contents failure: No buffer space available So I upped the buffers to 8M and when that ...
8
votes
1answer
396 views

TCP packet being retransmitted 7 times when sysctl tcp_retries1 is set to 3 - why?

Ubuntu 12.04 I am trying to better understand how many times TCP will attempt to retransmit a packet when it does not receive confirmation the destination received it. After reading the tcp man page ...
7
votes
5answers
15k views

Can only bring up one of two interfaces

I'm having a bizarre issue with my HP Proliant DL 360 G4p server. It has two gigabit ethernet interfaces but I can bring up only one of them. This is starting to freak me out and that's why I turned ...
7
votes
2answers
540 views

How can I switch from a custom linux network namespace back to the default one?

With ip netns exec you can execute a command in a custom network namespace - but is there also a way to execute a command in the default namespace? For example, after executing these two commands: ...
7
votes
1answer
307 views

Is ISP's Equipment Misconfigured? Getting Martian Packets on Internet Interface

We have a /28 block from our ISP. Let's say 1.1.1.240/28 with a gateway of 1.1.1.241. We are getting martian packets from another customer over at 1.1.1.214. They are sending broadcasts to 1.1.1.255. ...
7
votes
3answers
4k views

Layer 4 vs Layer 7 Load Balancing

I am trying to decide between using a layer 4 load balancing solution for my datacenter or a layer 7 solution. Unfortunately (for my sanity, that is), my use case is simple enough that both solutions ...
7
votes
3answers
29k views

Why ip route add doesn't work, but ip route add with less details and then change works?

I have a problem with ip route add. Surprisingly, I can add the route then change it, but I cannot directly add it: # ip route add 192.168.0.0/16 via 192.168.255.254 src 192.168.1.101 RTNETLINK ...
7
votes
2answers
2k views

Linux e1000e (Intel networking driver) problem with resume and pcie=off

This question is a continuation of this one. I've been having a ton of problems with my Ethernet chipset and e1000e driver: 02:00.0 Ethernet controller: Intel Corporation 82573L Gigabit Ethernet ...
6
votes
2answers
6k views

What is the correct way to open a range of ports in iptables

I have come across articles advising for the following: iptables -A INPUT -p tcp 1000:2000 -j ACCEPT And others stating that the above will not work and iptables only supports multiple port ...
5
votes
3answers
2k views

How to completely disable IPv4 stack from Linux?

How can I disable IPv4 stack from Linux ? I want to do that dynamically, ie. sometimes I want it enabled and sometimes I want only IPv6 stack. Is there any portable way to do that ? If you know how to ...
5
votes
3answers
2k views

How to see on Linux what network interface and source IP address is used for a route to a specific destination host?

If I have multiple network interfaces (here: 2) on a Linux machine (here: Debian Lenny). How do I see, over what network interface (NIC) a route to a specific destination host is going and what source ...
5
votes
3answers
3k views

Redirect output of mysqldump to scp

I worked with a linux pro years ago who did this nifty trick. He could do a mysqldump but redirect the output to an scp/ssh connection rather than writing to disk. We utilised this quiet a bit where i ...
5
votes
3answers
4k views

Ubuntu: disable udev's persistent-net-generator.rules

I'm using Ubuntu 12.04 LTS server edition and I am modifying /etc/udev/rules.d/70-persistent-net.rules to define my own mappings of ethernet interfaces to MAC addresses; that file is initially ...
5
votes
1answer
11k views

How GRO (generic receive offload) works on more advanced NICs?

I am interested in particular answers: Does the NIC with GRO edits/creates TCP ACK or any other packets (or is this feature transparent to receiver/sender TCP stacks)? There should be a ...
5
votes
3answers
330 views

Multiple ethernet interfaces

I have a two network cards, configured like this: eth0 Link encap:Ethernet HWaddr 00:19:d1:31:08:e8 inet addr:192.168.5.104 Bcast:192.168.5.255 Mask:255.255.255.0 inet6 ...
5
votes
1answer
3k views

Is it possible to close a socket with a shell command?

Is it possible to close a socket by using some sort of shell command/program? I've seen plenty of examples of manipulating sockets using C and other languages but have been unable to find a program ...
5
votes
1answer
376 views

IPv6 and NAT, routing to multiple ISPs

Currently I have a nice setup using private IPv4 address space and uplinks from two ISPs to the Internet. Thanks to NAT I can just take down one of the interfaces and the Internet access is still ...
5
votes
2answers
1k views

dynamic routing between openvpn tunnels

i'm thinking about using dynamic routing [ OSPF or RIP ] via OpenVPN tunnels. right now i have few offices connected in full mesh, but this is not scalable solution as we add more locations. i would ...
5
votes
3answers
2k views

Terminating MPLS vpn on Linux

Is it possible to terminate MPLS vpn connection on Linux and how? On my side Linux box has fiber ethernet interface and has fiber plugged in. We do not have any other router etc.
5
votes
2answers
3k views

I need a reverse proxy solution for SSH

Hi here is a situation I have a server in a corporate data center for a project. I have an SSH access to this machine at port 22.There are some virtual machines running on this server and then at the ...
5
votes
1answer
90 views

Load balancing network traffic using iptables

I am trying to load balance traffic from internal LAN on a linux router having two gateways. Initially I went for the iproute implementation which didnt balance the load as expected, reason being that ...
5
votes
1answer
4k views

Too many TCP connections causes disconnections

I have a game server which runs with TCP connections. Server disconnects users randomly. I think its related with TCP settings of server. In local development environment written code can handle ...
5
votes
1answer
10k views

RTNETLINK answers: File exists when executing 'service network restart'

Executing either command: sudo service network restart sudo ifup bond0 Results in the following error (and this is the only error): Bringing up interface eth0: RTNETLINK answers: File exists ...
5
votes
3answers
1k views

Broadcom BCM5716 Hangs on CentOS 6 Boot

I have a fresh CentOS 6 installation on a Dell R310 server with a Broadcom BCM5716. The onboard NIC is causing the boot to hang for some reason. Welcome to CentOS Linux Starting udev: udev: starting ...
5
votes
2answers
4k views

What do “Unknown SSAP” and “Unknown DSAP” mean in tcpdump?

While trying to fix a problem with intermittently losing internet connection on a machine with a wireless connection to a router, I ran tcpdump and noticed packets with "Unknown SSAP" and "Unknown ...
4
votes
2answers
3k views

Unable to ping, although can download packages

I've installed Debian Squeeze on a Dell PowerEdge server. However, I'm facing some problem with configuring the network. Although I can ping machines inside my network, I'm unable to d0 so outside the ...
4
votes
1answer
673 views

Listing the routing table takes long time to complete

When I print routes defined on my computer using route, it takes about 5 to 20 seconds to complete. Why does it take so much time? With VPN enabled: $ time sudo route Kernel IP routing table (...) ...
4
votes
4answers
7k views

Is it dangerous to change the value of /proc/sys/net/ipv4/tcp_tw_reuse?

We have a couple of production systems that were recently converted into virtual machines. There is an application of ours that frequently accesses a MySQL database, and for each query it creates a ...
4
votes
5answers
428 views

Arbitrary VLAN interface name

Is there a way to name a VLAN interface arbitrarily like eth72 or ext19 instead of the four standard nameing schemes eth0.72, vlan19 (and the padded variations)? Don't have no clue. Perhaps udev?
4
votes
5answers
6k views

Override DHCP hostname on RHEL5/CentOS/Amazon Linux

I'm running Amazon Linux (based on RHEL5) on EC2. I have my own domain name pointing to the instance's elastic IP. Amazon auto-assigns the instance a generic (and not visible on the Internet) ...
4
votes
3answers
13k views

How to “restart” particular network interface on RHEL?

In RHEL, instead of using service network restart command, how can i restart a particular network interface, lets say "eth1", with only one command. "Only one command" because that is the only ...
4
votes
1answer
7k views

How to troubleshoot latency between 2 linux hosts

The latency between 2 linux hosts is about .23ms. They are connected by one switch. Ping & Wireshark confirm the latency number. But, i dont have any visibility into what is causing this latency. ...
4
votes
1answer
8k views

NAPI vs Adaptive Interrupts

Could anyone please explain how two following technologies are used to mitigate interrupt overhead under high networking load? Adaptive-rx/Adaptive-tx, and NAPI; I would appreciate an answer that ...