The Crucial Blog - Archive
How to install dig on Ubuntu or Debian
To install the dig command on Ubuntu or Debian run the following:
apt-get install dnsutils
Tags: debian, networking, server-administration, ubuntuNo Comments
Filed under: Uncategorized by — aaron @ 8:24 pm
ip_conntrack: table full, dropping packet.
If you see something like the following in your log files:
ip_conntrack: table full, dropping packet.
printk: 73 messages suppressed.
ip_conntrack: table full, dropping packet.
printk: 84 messages suppressed.
ip_conntrack: table full, dropping packet.
printk: 157 messages suppressed.
ip_conntrack: table full, dropping packet.
printk: 145 messages suppressed.
ip_conntrack: table full, dropping packet.
printk: 118 messages suppressed.
ip_conntrack: table full, dropping packet.
printk: 121 messages suppressed.
ip_conntrack: table full, dropping packet.
printk: 93 messages suppressed.
ip_conntrack: table full, dropping packet.
printk: 128 messages suppressed.
ip_conntrack: table full, dropping packet.
It will probably look like you are experiencing a network issue with a lot of packet loss, but in fact it isn’t one at all!
This error has to do with the value in /proc/sys/net/ipv4/ip_conntrack_max set to low, and letting the system only handle a few connections at once. This value is usually imposed when APF is installed, and the following should be done to correct it:
echo “138304″ > /proc/sys/net/ipv4/ip_conntrack_max
add the following to /etc/sysctl.conf:
sys.net.ipv4.ip_conntrack_max = 138304
If you are running APF modify the following line to:
SYSCTL_CONNTRACK=”138304″
To check what the current value is you can use:
cat /proc/sys/net/ipv4/ip_conntrack_max
Tags: linux, networking, server-administration(4) Comments
Filed under: Uncategorized by — aaron @ 2:22 pm
Setup default route/gateway on Linux using the route command
Sometimes Linux does not properly create the default gateway, so you may need to add it manually. You can add a default gateway using the route command:
View Routing Table:
route -n
Add default route:
Tags: linux, networking, server-administrationroute add default gw 192.168.0.1 eth0
No Comments
Filed under: Uncategorized by — aaron @ 5:54 pm
Xen: Dom0 and DomU can ping, but no other network connectivity – checksum problems
This appears to be a long standing bug with Xen which has not yet been fixed, it has shown its face in a few of our servers recently – but not all. Basically once Xen is installed on Dom0 you are able to ping it, however anything other network services do not work, such as SSH. From what I have read this is due to checksums being done in numerous places, and seems that there is a bug somewhere while this is being done which results in the checksums not matching, and the packets being dropped. The solution to this is to run the following:
ethtool -K eth0 tx off
This same issue arises in the DomUs (Guest) , and the same fix can be used. Its probably a good idea to place in /etc/rc.local on Redhat/Centos/Fedora systems.
Tags: networking, server-administration, vps, xen(3) Comments
Filed under: Uncategorized by — aaron @ 11:20 pm
Where did netconfig go? (CentOS/RHEL)
I recently noticed that netconfig had recently disappeared from CentOS 5/RHEL 5 so did a bit of research and found that netconfig has been replaced by system-config-network.
Tags: linux, networking, system administrationNo Comments
Filed under: Uncategorized by — aaron @ 7:40 pm
Configuring Network Interfaces on CentOS, Redhat, Fedora Core, and Debian
CentOS/Red Hat/Fedora Core:
The network configuration files are in the folder:
‘/etc/sysconfig/network-scripts’
The files for the interfaces will be ifcfg-eth0, ifcfg-eth1, ifcfg-eth0:0 (if there are sub-interfaces)
Static IP address configuration:
——————–
[root@sXXX network-scripts]# cat ifcfg-eth0
# Intel Corporation 82573L Gigabit Ethernet Controller
DEVICE=eth0
BOOTPROTO=static
HWADDR=YY:YY:YY:YY:YY
BROADCAST=XXX.XXX.XXX.XXX – specify the broadcast address here
IPADDR=xx.xx.xx.xx – specify the IP address here
NETMASK=255.255.255.0 – specify the netmask here
ONBOOT=yes
TYPE=Ethernet
———————-
Please specify ‘ONBOOT=yes’ which will activate the interface upon system boot
Dynamic IP address configuration: Change BOOTPROTO value to dhcp
——————–
[root@sXXX network-scripts]# cat ifcfg-eth0
# Intel Corporation 82573L Gigabit Ethernet Controller
DEVICE=eth0
BOOTPROTO=dhcp
ONBOOT=yes
TYPE=Ethernet
———————-
To bind a range of IP address, create a file called ifcfg-eth0-range0 (for example eth0:0, eth0:1, etc)
The entries should be:
——————————-
IPADDR_START=192.168.0.10
IPADDR_END=192.168.0.20
CLONENUM_START=0
NETMASK=xxx.xxx.xxx.xxx
——————————–
IPADDR_START: This is the first IP from the address range you want to bind to your ethernet device.
IPADDR_END: This is the last IP from that address range.
CLONENUM_START: This is the number that will be assigned to the first IP alias interface. For instance, if your Internet interface is eth0 and CLONENUM_START is 0, then this config file will create 10 interfaces starting with eth0:0 (eth0:0, eth0:1, eth0:2 etc) and ending with eth0:10.
The gateway for the network can be specified in the file ‘/etc/sysconfig/network’
——————————-
NETWORKING=yes
HOSTNAME=hostname
GATEWAY=”XXX.XXX.XXX.YYY”
———————————
Once you assign the IP addresses and configure the gateway please restart the service network ‘/etc/init.d/network restart’
You may also use ‘/usr/sbin/system-config-network-tui’ to configure the network interfaces
Debian:
In Debian the interface configuration file is ‘/etc/network/interfaces’
The entires are:
———————————
auto lo
iface lo inet loopback
auto eth0
iface eth0 inet static
address xxx.xxx.xxx.xxx
netmask yyy.yyy.yyy.yyy
broadcast xxx.xxx.xxx.xxy
network xxx.xxx.xxx.xxz
gateway xxx.xxx.xxx.xxw
———————————
After you configure the network interfaces restart the network service using ‘/etc/init.d/networking restart’
Tags: centos, debian, fedora core, networking, system administrationNo Comments
Filed under: Uncategorized by — aaron @ 12:01 am
How to view current configuration on a Cisco Pix 520-UR Firewall
First console into the switch, then do the following:
firewall> enable
Password: ************
firewall# configure terminal
firewall(config)# wr term
Building configuration…
: Saved
:
PIX Version 5.0(2)
nameif ethernet0 outside security0
nameif ethernet1 inside security100
nameif ethernet2 pix/intf2 security10
….
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Filed under: Uncategorized by — aaron @ 1:11 am
Accessing a Cisco Switch or Router via Serial Port on Linux Using Minicom
If you need to access a Cisco swith or router on Linux (Redhat, CentOS, Debian, etc) then install minicom, and do the following.
Firstly you can check which serial ports on your computer are available:
dmesg | grep tty
ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
ttyS1 at I/O 0x2f8 (irq = 3) is a 16550A
Then run minicom:
minicom /dev/ttyS0
Type:
Ctrl + A Z
Then type ‘o’ (the letter, not number) and select ‘Serial port setup’ to configure minicom. Here is a sample configuration of what you want your configuration to look like:
A – Serial Device : /dev/ttyS0
B – Lockfile Location : /var/lock
C – Callin Program :
D – Callout Program :
E – Bps/Par/Bits : 9600 8N1
F – Hardware Flow Control : Yes
G – Software Flow Control : No
To get to here, please read the following:
Ensure the correct serial port is being utilized by pressing A, the port you will usually be using is /dev/ttyS0
Press E to configure bit rate, then select E again, and then Q and Enter.
Ensure Hardware Flow Control is on, and Software Flow Control is off.
If you are having issues, try exiting and re-opening minicom, or disconnecting and reconnecting your console cable.
Tags: cisco, linux, networkingNo Comments
Filed under: Uncategorized by — aaron @ 12:25 am