0
votes
0answers
8 views

A question in ip_append_data [migrated]

I am confused with ip_append_data in linux network protocol stack when I see those codes: if (!(rt->u.dst.dev->features&NETIF_F_SG)) { unsigned int off; off = ...
1
vote
1answer
31 views

Binding to not existing interface

I've just noticed the very weird situation I don't have a good explanation for. The machine (debian) has one interface with one IP address assigned: # ifconfig vmbr0 |grep inet inet ...
9
votes
4answers
142 views

Why does *BSD uses driver specific names for network interfaces? Does it imply limitations?

I notice that depending on the brand of the network card, interface names differ (driver dependent I suppose). Why does *BSD uses driver specific names for network interfaces? Does it mean there is ...
0
votes
0answers
615 views

Ping IP works, nslookup fails. New Kernel

I am compiling my own 3.14 kernel. I fear I may have left out some important networking feature to get DNS working. I can't resolve domain names. I can ping my DNS server. I can resolve using that ...
1
vote
1answer
78 views

Kernel optimiziations for ioctl AF_INET operations

Our server solution handles many tunnel operation requests (add/update/delete) using the ioctl interface, and the AF_INET address family socket. Aprox. numbers are 100 operations/minute with over 8k ...
1
vote
1answer
184 views

Does an in-kernel firewall sit between the network access layer and Internet layer?

This question is a follow-up to my previous question. Logic for me to says that an in-kernel firewall sits between the network access layer and the Internet layer, because it needs to have access to ...
3
votes
1answer
95 views

How security programs like firewall, IPS and IDS have access to network data?

It is said that kernel responsible for the transport, internet and network access layers for a network data. Then, the network data is passed on the appropriate process based on port number. How ...
6
votes
3answers
413 views

How does one capture traffic on virtual interfaces?

I would like to capture traffic on Linux virtual interfaces, for debugging purposes. I have been experimenting with veth, tun and dummy interface types; on all three, I am having trouble getting ...
2
votes
1answer
60 views

How does the kernel know which file descriptor to write data to after fork() in a concurrent server?

Basic concurrent client/server architecture: There's a main loop listening for requests on a port (for example 3000), after accepting the connection the server spawns a child process that ends up ...
0
votes
1answer
77 views

How do I verify that the Linux kernel is not freezing when uploading or downloading large data over the ethernet interface?

How to verify if the Linux kernel is doing what it's saying for network interfaces? I have one network interface eth0 which has hardware support to do 1GB full-duplex. I have prepared 2 box. Now ...
2
votes
1answer
93 views

Server pinning one core

I'm working on a server using Vert.x in Java and I'm noticing some performance problems when running on a dedicated server running Ubuntu 12.04. The server picks up the incoming HTTP requests, does ...
6
votes
1answer
351 views

Is “zero-copy networking” implemented by default on Linux?

I saw this article: http://lwn.net/2001/0419/kernel.php3 Zero-copy networking will be in 2.4.4. This patch, by David Miller, Alexey Kuznetsov, and others, has been in development and testing ...
1
vote
1answer
291 views

ixgbe: increase rx performance

I have an Intel 82598EB 10GBE NIC. I need to receive traffic without packet loss. Data rate is 4-5 Gbps, packet size is 1500-9600 bytes. I had already configured smb and irq affinity. I also tried ...
1
vote
1answer
533 views

Enable kernel module for VPN

I'm trying to turn on modules for VPN so I followed this tutorial to compile new ubuntu kernel 3.8.6 . But the features I've turned on using make menuconfig seem not to be enabled. (the features I ...
0
votes
2answers
39 views

can't update with this error messg

I got this message: not enough free disk space.... The upgrade needs a total of 31.8 M free space on disk '/boot'. Please free at least an additional 31.8 M of disk space on '/boot'. Empty ...
0
votes
1answer
284 views

How to troubleshoot high kernel time (high network usage; high interrupts)

I've noticed that I have high kernel time when doing a lot of network traffic in Linux. I also noticed that 45% of my CPU is spent doing interrupts. How can I further troubleshoot this?
2
votes
0answers
292 views

Failed to execute shell script from “network” udev rule to change the MAC-address

I am trying to execute a shell script from udev rule, when a network interface is added, as follows: SUBSYSTEM=="net", ACTION=="add", KERNEL=="eth*", PROGRAM="/usr/local/bin/changemac.sh", ...
2
votes
1answer
390 views

What does “kernel-resident” mean?

Quoting from the ifconfig man page: ifconfig is used to configure the kernel-resident network interfaces. It is used at boot time to set up interfaces as necessary. After that, it is ...
2
votes
1answer
1k views

SCTP support for Linux kernel 3.3.4-5.fc17.x86_64

I'm using Fedora 17 64-bit version, with Linux kernel version 3.3.4-5.fc17.x86_64. I installed lksctp using yum. sudo yum install lksctp-tools.x86_64 When I try to run sctp_status -H 127.0.0.1 ...
2
votes
2answers
645 views

SIOCSIFADDR: File exists after upgrading kernel

Since upgrading my (Gentoo) kernel from 2.6.38 to 3.3.8 (via oldconfig), I can't get the network on eth0 up anymore. It reports "SIOCSIFADDR: File exists" with a number of other SIOCSIF* errors that ...
4
votes
1answer
1k views

How can I use netconsole to help solve a kernel panic?

When I try to use a raid as root, my system panics. I want to read the kernel output right before the panic, but can't scroll up. After Googling a bit, I wanted to try netconsole. but I get no output ...
4
votes
2answers
2k views

How to know if a network interface is tap, tun, bridge or physical?

As far as i know, there are 4 main types of network interfaces in linux: tun, tap, bridge and physical. When i'm doing sys admin on machines running KVM, i usually come accross tap, bridge and ...
1
vote
1answer
548 views

Wireless not showing a network in the scan results

I have a weird problem of connecting to a wireless network. I am connecting to a network named "C-202" with WPA-Personal. This network shows up in the scan results some time and won't show some time. ...
3
votes
1answer
2k views

Debian 6.0 system with 2.6.39 kernel dropping packets, sandy bridge hardware

I recently migrated an existing Debian system to new hardware, a core i3 chip running on an intel sandy bridge motherboard. I’m experiencing a very strange problem; when I ping my router, about 50% of ...
2
votes
2answers
323 views

UDP multicasting broken after kernel update

I've got an embedded system which is running a stripped down Gentoo userland with a manually build kernel. The system acquires data from a PCI card and sends it out to an UDP multicast group. All ...
9
votes
1answer
6k views

Buffer size for capturing packets in kernel space?

Going through the man page of tcpdump, it seems kernel can drop the packets if the buffer is full. I was wondering if: that size is configurable and/or where can I see the size for my distro? From ...
18
votes
2answers
12k views

how to check rx ring, max_backlog, and max_syn_backlog size

Quite often in the course of troubleshooting and tuning things I find myself thinking about the following Linux kernel settings: net.core.netdev_max_backlog net.ipv4.tcp_max_syn_backlog ...
4
votes
1answer
308 views

NetBSD 5.1 NDIS Kernel Compile Error

I have an old Toshiba Satellite 4015CDT, with Pentium II MMX, 32MB RAM, 4GB HDD. It also has one USB 1.0 port, parallel and serial ports, a 3.5" floppy drive and a CD-ROM drive (almost dead). I've ...
2
votes
2answers
908 views

no network device found after Kernel update

So I managed to install Debian 5 on an eBox 3300MX (an embedded type computer). I added a custom kernel after getting a basic install done. That was to get the network card to work. After that, I ...
7
votes
1answer
4k views

What is the loopback interface

What is the loopback interface and how does it differ from the eth0 interface? And why do I need to use it when mounting an ISO or running a service on localhost?