CentOS 5 Networking :: Multiple NICS In Same Machine Connected To The Same Switch?
Dec 8, 2009
I have a program that attaches to an interface. I can run two copies of the program on two systems (each running one instance), connect it to a switch, say 1.1.1.1 & 1.1.2.1. In this configuration two instances of the program can communicate and everything is fine.
Now, to reduce cost, it want to use only one system with two nics connected to the same switch, running two instances of the above program, each instance attached to two interfaces respectively on the system. I have the following settings:
eth1 Link encap:Ethernet HWaddr XXXXXXXXXXXXXXX
inet addr:1.1.1.1 Bcast:1.1.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
eth2 Link encap:Ethernet HWaddr XXXXXXXXXXXXXXX
inet addr:1.1.2.1 Bcast:1.1.2.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
[Code]...
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Dec 7, 2009
I have a program that attaches to an interface. I can run two copies of the program on two systems (each running one instance), connect it to a switch, say 1.1.1.1 & 1.1.2.1. In this configuration two instances of the program can communicate and everything is fine.Now, to reduce cost, it want to use only one system with two nics connected to the same switch, running two instances of the above program, each instance attached to two interfaces respectively on the system. I have the following settings:
eth1 Link encap:Ethernet HWaddr XXXXXXXXXXXXXXX
inet addr:1.1.1.1 Bcast:1.1.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
[code]....
However I cannot ping one from the other.
Neither "ping -I eth1 1.1.2.1" nor "ping -I eth2 1.1.1.1" works.
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Jun 16, 2009
I have a CentOS 5.3 box with three network interfaces in it. Each interface is attached to a separate VLAN and I want traffic to stay on each network segment.What I can�t figure out is why I cannot get each interface to have its own gateway and everything gets sent through the default gateway.The basically takes my possible 3Gb total bandwidth and throws it down a single 1Gb pipe.Then on top of that, if I take down the interface (ifdown) that has the current default gateway,I loose contact to the other two interfaces.When I look at the routes, each one of the interfaces shows the gw as 0.0.0.0 and defers to the default route. So I delete the route and try to add a new route with:
[root@testsan ~]# ip route add 10.1.15.0/24 via 10.1.15.1 dev eth2
but end up with the error:
RTNETLINK answers: Network is unreachable
[root@testsan sysconfig]# cat network
NETWORKING=yes
NETWORKING_IPV6=no[code].....
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Mar 30, 2009
I have a motherboard which has 4 x 1Gbps Ethernet controllers. I would like to use it as a Gateway for my home network. I have a static IP from my ISP which I can use to configure eth0 (I haven't done it yet as the LE-565 is currently sitting behind my Netgear router until I've got DHCP working). I would like to use eth1, eth2 and eth3 for my LAN. How do I set things up so that DHCP is handing out IP addresses on the same subnet (192.168.0.0/24) on all three interfaces?
P.S. I think what I'm asking is: how do I combine all 3 interfaces to behave like a switch (ie. just like my Netgear router)?
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May 20, 2010
I have an old pentium 3 computer that has ~7 NICs installed. These NICs are attached to modems and other networking equipment. According to the linux ping page on computerhope.com, it seems that one could send a ping from a certain specified NIC. How would one go about this?
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Jan 25, 2011
We have two recently installed centos machines, each running 5.5, and hosting an elastix pabx distro as well as a Virtual PC instance. On both machines, the network adaptor fails completely every week or so. As they are remote machines, the only option we have when this happens is a manual reboot.
I might be barking up the wrong tree here, but the only significant difference on these machines to others we have deployed is the Virtual PC instance. The machines have dual ethernet ports, with one assigned to the virtual PC. When the network failure occurs, it does not effect the virtual machine, which continues along merrily.
My expert colleague does not think so, but can anyone think of any way that our configuration could be causing the problem? If not, does anyone have any ideas on what the problem could be, or where I would start looking for information on the machine to debug the issue?
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Aug 21, 2010
I currently have a command line Ubuntu 9.10 installation.
I wish to be able to have either both wireless and wired connection working
For example: when LAN is connection the wireless is switched off, when LAN is disconnected the wireless comes up (WPA2)
I know that the Network Manager in Gnome does this auto switching for you but I need to know how to do this in command line only.
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Jan 18, 2010
I have a Proliant DL 120 G5 with CentOS 5.4 and I have installed a Brodcom Corporation Netxtrem BCM 5722 Gigabit Ethernet PCI. So I have two interfaces: eth0 broadcom eth1 Intel The eth1 works, instead eth0 don't work. I can ping itself and 127.0.0.1 but I can't ping the gateway. The results of netstat -nr is:
[code]....
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Feb 23, 2010
My setup is as follows:
eth0 - lan ip
eth1 - WAN ip
I have installed a sip server on the box. From the box I would like to access machines on wan and lan. First of all, is it possible? If yes, I have setup up the nics with default wan gateway. However, when I try to ping wan url, no response. Are there other things I need to do to accomplish this?
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Mar 31, 2011
configuring DHCP server with two NICs. I need DHCP server with 2 NICs:
eth1 - 192.168.103.11
eth2 - 192.168.123.11
The client also has two NICs and suppose to receive ip addresses eth1 from 192.168.103.0 and eth2 from 192.168.123.0 Here is the dhcpd.conf from dhcp server:
ddns-update-style interim;
authoritative;
ignore client-updates;
[code]....
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Nov 9, 2009
I have configured CentOS 5.4 as a router/firewall (iptables) as such, and it is working fine:
eth0 - Public IP/Intenet, DHCP
eth1 - 192.168.0.0 internal "net1"
eth2 -10.0.0.0 internal "net2"
I want to add a fourth NIC, eth3, which will be assigned its own Public IP/Internet address (thru DHCP; my ISP provides two). The purpose it to route all net1's internet-bound traffic through eth0, and all of net2's internet traffic to eth3. This allows me to use one router/firewall machine instead of two separate ones. I anticipate that without some specific routing instructions, the default route will be eth0 for all net1 and net2 internet traffic (eth3 will be ignored).
I thought of using just one NIC (eth0) but create an alias (eth0:0), but IPtables (and possible DHCP) can't differentiate between the two (besides, nics are inexpensive). Is there a way to do this through routing commands, or even use iptables prerouting/forward functions (or is using iptables problematic)?
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Dec 23, 2010
I got a Ubuntu machine running a local web server. It is connected to an archaic 10mbit hub, and I'd like a little bit faster network. I got a new 100/1000mbit switch connected to my router. I have 3 other PC's running off it, no problems at all. No configuration was necessary, and all existing cables worked fine.
Since the router and hub are located at the opposite end of the house, and the switch is in my PC room, I made up a new cable to connect it to my Ubuntu machine. It's just a straight-through cable, just like the other cables connecting the switch to other PC's. Okay so, when I plug the cable in to the machine I get no ethernet lights on either the machine nor the switch. But here's the kicker: I plug the cable into my laptop (running Windows 7), and it works perfectly. I restart the machine with the cable in, and get a green light. As soon as Ubuntu loads up, no lights, no connectivity. It shouldn't matter, but I'm running a static IP on the machine. I also have static IP's on the other PC's connected to the switch and nothing had to be changed.
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Jul 9, 2011
I am trying to ping my Windows machine connected to an open network (I'm at a internet caf) from my linux VM (also connected to the same network with a usb adapter), but I'm obtaining this output:
# ping 10.23.47.12
PING 10.23.47.12 (10.23.47.12) 56(84) bytes of data.
From 10.128.128.1 icmp_seq=1 Packet filtered
From 10.128.128.1 icmp_seq=2 Packet filtered
With high probability host 10.128.128.1 is a firewall or some router with packet filtering mechanism; but I don't understand how it can be possible to implement this kind of solution, with what kind of software or hardware? I also tried a nmap scan to my Windows machine but it returns me scan results from another host(the firewall or the router I suppose):
nmap -sS -O -P0 10.23.47.12
Starting Nmap 5.51 ( http://nmap.org ) at 2011-07-09 15:46 CDT
Nmap scan report for 10.23.47.12
Host is up (0.097s latency).
All 1000 scanned ports on 10.23.47.12 are filtered
[Code]...
So my questions is, how is technically possible to implement this kind of restriction within hosts connected on the same network? It's the first time I see this kind of configuration.
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Oct 15, 2010
configure a server with two network interfaces? This system is physically moved from one network to another every few days (different buildings but connected by a VPN). I'd like to be able to control the IP address of the system depending on which port I plug the network cable into with a static setting. Right now the system will connect to the local network, but any requests to go beyond the subnet get lost. The only way I can get the system to talk outside of its subnet is to comment out the second interface.
/etc/network/interfaces:
auto lo
iface lo inet loopback
auto eth0
[code]....
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Oct 15, 2010
I can connect to my school's wireless network using the standard network manager, but often (not always) it repeatedly disconnects and reconnects every few minutes. Occasionally it also prompts me for the security information again (even after it previously connected successfully).
By running iwconfig when it's on the fritz, I can see that it's often switching access points for the network - which is what I think is causing the problem. It disconnects and reconnects even when the signal strength for the current AP is fine, and it will often switch to an AP with a weaker signal strength.
$sudo lshw -C network
Code:
description: Wireless interface
product: Realtek Semiconductor Co., Ltd.
vendor: Realtek Semiconductor Co., Ltd.
physical id: 0
bus info: pci@0000:05:00.0
logical name: wlan0
[Code]...
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Nov 20, 2010
I have an Asus R1F laptop with a build in wireless card. I also have 2 USB dongles that we used to use old desktop machines. All of the cards work fine in Ubuntu. I'm running Ubuntu 10.10, 2.6.35-22-generic-pae.
The problem is that I have really bad signal on my side of the house and the connection is dropped quite often. I've tried just connecting on the devices at the same time, they all connect fine but nothing actually works. I read about bonding interface cards on this blog and that would solve all my problems - if a usb dongle could act as a backup for when the normal connection is dropped and while it is reconnecting.
I tried what was written and also did some Googling, but every way that I try seems to work fine until 2 wireless devices are bonded. When that happens they both disconnect and reconnect like crazy. This happens both with and without network manager running.
Build in card[wlan0]: Intel PRO/Wireless 3945ABG
USB[wlan1]: Cisco LinkSys Compact Wireless-G USB Adapter
USB[wlan2]: Realtek RTL 818713 WLAN Adapter
I load the module:
Code:
modprobe bonding mode=1 miimon=100 downdelay=200 updelay=200
[Code]...
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Apr 22, 2011
I have an Ubuntu server box with multiple NICs. I'd like to specify that all traffic bound for a certain IP range goes through one NIC, and everything else goes through the other. Does anyone know how to do that? I'm not a total newbie, but I'm also not a linux guru (but usually can google my way to a solution...usually).
ETA: Source and destination IP for routing.We have 1 NIC with a public IP, all public IP's should talk to it.Another NIC with a private IP, all private traffic should talk to this.In practice, I have some devices on a different subnet of the public IP range we have that will only talk to the private IP.
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Oct 31, 2009
I have two machines, one has XP service pack2, second one has CentOS 5.3 (Linux), they are connected through crossover cable. I have configured everything fine but don't know why till now can't ping!
A. Windows machine settings as follows:
IP Address: 192.168.1.3
Subnet Mask: 255.255.255.0
Default Gatway: 192.168.1.1
+ Firewall is turned OFF.
B. For Linux machine, I will list everything stored in network files, logged as [root@localhost ~]# :
1. /etc/sysconfig/network:
ifconfig eth0 192.168.1.4 netmask 255.255.255.0 up
route add -net 192.168.1.0 netmask 255.255.255.0 eth0
route add default gw 192.168.1.1 eth0
NETWORKING = yes
NETWORKING_IPV6=no
HOSTNAME=localhost.localdomain
2. /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE="eth0"
IPADDR="192.168.1.4"
NETMASK="255.255.255.0"
ONBOOT="yes"
BOOTPROTO="yes"
3. /etc/resolv.conf
nameserver 192.168.1.4
search locadomain
4. I restarted network service using this command:
/etc/init.d/network start
everything is fine. When checking using ifconfig command. I get the following:
eth0 Link encap: Ethernet HWaddr 00:08:0D:EE:19:66
inet addr:192.168.1.4 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr:........
[code]....
I mean I assigned the IP: 192.168.1.4 to Linux machine (Eth0). I did everything above and can't ping till now, when pinging from windows or Linux I get a message "destination host unreachable" restarted Linux many times but same result. NETWORK CABLE is working fine I tested it.
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Mar 15, 2011
I am trying to get preseed working on a bunch of machines with multiple NICs but it doesn't pick the right interface and/or gets "no link" on all interfaces. My PXE kernel line looks like so (I have auto=true priority=critical and interface=auto)
label squeeze
kernel debian-installer/squeeze/i386/linux
append vga=788 initrd=debian-installer/squeeze/i386/initrd.gz auto=true priority=critical ramdisk_size=10800 root=/dev/rd/0 rw url=example.com/d-i/squeeze/preseed.cfg interface=auto netcfg/dhcp_timeout=60
[Code]...
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Dec 13, 2010
I am find myself in need of building what amounts to 3 ip networks on 1 physical lan.
first LAN is another companies network on the 10.0.0.0 network a mix of pc's and equipment
second is LAN new company network 192.168.168.0/24
third network is an ip phone system for both i would like to use 192.168.200.0/24
i am hoping to use the same dhcp server to do this, assigning address to the old company's 10. network via mac address reservation.
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Dec 10, 2009
I am using centos 5.4, recently i come to know that people are'nt able to connect to my system using ssh.1. but i can easily connect to them. 2. I checked the firewall settings also, it seems ok to me.3. I tried restarting sshd also. " /etc/init.d/sshd restart " but to no avail.4. Before when i was using 5.3, it was not a problem..!!5. I tried the following command on other system. It shows the following output.
# ssh -v -l niks 43.88.101.99
OpenSSH_4.3p2, OpenSSL 0.9.8e-fips-rhel5 01 Jul 2008
debug1: Reading configuration data /etc/ssh/ssh_config
[code]....
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Apr 14, 2010
Basically the situation is that the boot hangs if my USB KVM switch is connected. The keyboard works fine through the KVM switch to access the BIOS menu and in the grub2 menu, but as soon as it starts to boot, I get a black screen with a white cursor on top which never goes anywhere.The weird part is that if I disconnect the KVM and reboot, it gets past this point and I can reconnect the KVM and both the mouse and keyboard work normally.However, even if I plug the keyboard in directly but leave the KVM plugged in, the boot hangs. Something about the fact that the KVM is connected (rather than not detecting keyboard) is causing the boot to stall.
The even weirder part is that this worked fine on my previous build, which was 8.04 upgraded sequentially to 9.10. But my system drive died so I rebuilt directly from 9.10 ISO and now this does work. I have tried downgraded to grub .97, I have tried switching between server and generic kernels.This seems to be the same issue reported in[URL]
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Aug 4, 2010
We are working on a project to create a display wall of 8 monitors arranged as 2 high by 4 wide. Each monitor is connected to a single machine and all machines are networked with a master machine with its own, seperate monitor.
Our goal is to get the 8 machines to share a single desktop, with the master machine acting as the server. We have looked at using Xinerama or NMM, but we are unsure about how to get started configuring the multi-machine, multi-head display.
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Jan 25, 2009
Assume I installed originally CentOS Desktop with IP receiving from DHCP server.Later I decided to assign a fixed IP to the local CentOS installation.How do I switch (permanently) the dynamic DHCP IP assignment to a fixed IP?
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Jan 5, 2011
Anyone knows a way to switch automaticaly the ouput device to bluetooth headset when is connected?I'm using Fedora 14.
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Jul 27, 2011
I have router based on CentOS system with DHCP server. In one eth I have fiber converter attached in second one I have Cisco Catalyst switch connected. From the switch rest of ports are used to provide internet traffic to rest of network. I wanted to divide each segment of network (based on switch ports) that they don't see each other (it'll be good for me if someone will connect his wireless router to the network not to WAN by LAN port and start be a second DHCP server). So my network configuration:
CentOS:
DHCP with range 10.0.0.1/8 network
Switch ports
1 - CentOS DHCP
2 - second server
[code]....
Parts of networks I've assigned IPs 10.network_part.subnet_part.client_ip so I have addresses for clients: 10.1.1.2/8, 10.2.1.3/8, 10.3.0.4/8, etc ...
I've decided to give each port it's own VLAN like below:
Port / VLAN
1 / trunk
[code]....
I've configured switch ports by using:
(config)# interface Gi0/Port_Number
(config-if)# switchport access vlan VLAN_NUMBER
[code]....
And after doing that whole network stopped working. I think that cisco part of configuration is OK (at least customer ports, I don't know if there is any additional info needed for trunk port). On CentOS router I didn't setup anything regarding VLANs ...
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Mar 11, 2010
I followed the instructions on this page ([URL]) in order to secure my sshd and prevent anyone form accessing the server directly as root. Therefore I changed the "PermitRootLogin yes" to "PermitRootLogin no" and restarted sshd. After that root access was denied directly but for some reason I am unable to switch to root from any of the normal user accounts with "su -" because I keep getting the "Incorrect password" errors. I am sure that the password is correct but for some, to me unclear, reasons I am unable to access the root account over SSH from a normal user account. I also noticed that after that I lost the ability to access the server as root over SFTP. why I am unable to generally use the root account after doing the named changes to sshd_config/ I am running CentOS 5.4 with the newest update.
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May 11, 2010
I installed the CentOS v5.4 on a virtual machine vmware server v1.0. I put the the vmware ethernet on bridged mode and now I have an ip address, subnet mask and dns from my dhcp server from the the office where I am. I edit the file /etc/sysconfig/network and I put there the gateway ip. Now is okay but not at my home where I have another gateway ip. a script who switch between my gateways ?
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Jan 7, 2011
I had something I think if very odd happen to one of my computers at work today, it appears to have spontaneously switched from having a static address set to getting its address by dhcp.this is a small office with a mix of mostly linux servers and desktops with a few stand alone windows computers, mostly notebooks. Most of the desktop computers get their address by dhcp, they all have NIS /NFS for remote mounted home directories (interchangeable desktops so anyone can log in at any desk). The particular desktop computer in question here has a shared printer on its parallel port, so has a static IP. Yesterday a UPS in the server rack died, after pulling it and plugging things back in and restarting the servers, it was easiest just to reboot all the desktops, everything came up ok including the desktop in question, and the printer did work.
Today I pulled the oversized UPS from this desktop to replace the dead one, and put a more appropriately sized one in its place, shut the servers down again, rebooted, etc,About an hour later someone tells me the printer is not working on the desktop, and after a lot of searching I find this desktop has the wrong IP address, I ran system-config-network and it showed the address was set to dhcp, I changed this back to the correct static IP and things seem to be working ok now.
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Nov 26, 2009
Suppose that it is not convenient to go behind a machine to have a look.So I want to use a command to show whether the cable is plugged into network card. (Media connected or not)Can ifconfig do this? Or another one?
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