CentOS 5 Networking :: Multiple NICs On The Same Subnet?
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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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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Jan 8, 2010
I have 2 x PCs and a NAS. Both PCs have 2x NICS. PC connectivity to Internet is via an ADSL router. Current config: Thus far (by choice) I've used static IPs in the 192.168.168.x range for my internal network, connecting all PCs and NAS via a jumbo frame enabled gigabit switch. This has facilitated moving data between the PCs and the NAS at high-speed. As both PCs also required Internet access from time to time, both are also connected to the ADSL router using the 2nd NIC and using subnet 192.168.1.x. I'm sure some of you are shaking your heads by now, but it works well and has been entirely hassle free.
However, I've an app running on the NAS that I'm keen to get Internet connected also. As my existing network devices are not using DHCP I figured the simplest method would be to change my ADSL router configuration such that it is in the same 192.168.168.x subnet, change its DHCP server settings to serve IPs in the same subnet (but in a restricted range I know won't cause any conflicts with the static IPs) and problem solved. On changing the ADSL router confiruration with all machines already booted up and configured as described above, everything worked. All devices could see one another, and access the Internet. On later rebooting the system this no longer works
- Internet access is fine but PCs don't see one another or the NAS. If I disconnect the ADSL Router from the PCs then all devices see one another again.
- Does having 2x NICS on a single device each assigned unique IPs in the same subnet create an issue and can it be overcome? I'd like to overcome it because making one of my PCs the gateway forces me to have it on anytime another device needs access.
- If I'm forced to use Internet connection sharing with one PC on the network connected to the router, how do I best configure this?
- One of the things I need to retain is gigabit connectivity between the PCs and PCs and the NAS (currently achieved by 192.168.168.x subnet being linked via gigabit switch).
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Aug 2, 2010
I'm trying to work out how to route all traffic destined for the internet from all devices connected to eth0 to a wireless router access point via wlan0 on my Slackware box. I also have dhcpd providing ip addresses on the same subnet to any device connected to both eth0 and wlan0.
Diagram:
Code:
____________ ____________
[ ]=============> (wifi) ==============>[ Router / ]
|Workstations| __________ |Access Point| 192.168.2.1
[____________]==>(eth0)==>[ ]<==(wlan0)==>[____________]
192.168.2.253| Server |192.168.2.254
[__________]
If I connect to the router/access point via wireless or directly to the Server via a crossover cable I can obtain an ip address from dhcpd, so that works. As far as I can see I just need to how to route between eth0 and wlan0 then I can provide internet access to those devices!
ifconfig:
Code:
eth0 Link encap:Ethernet HWaddr **:**:**:**:**:**
inet addr:192.168.2.253 Bcast:192.168.2.255 Mask:255.255.255.0
inet6 addr: fe80::201:2eff:fe27:aea3/64 Scope:Link
UP BROADCAST MULTICAST MTU:1500 Metric:1
[code].....
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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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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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Jun 21, 2010
I have a network with multiple subnets from 10.12.056.0 to 10.12.060.0 using net-mask 255.255.248.0 and one gateway 10.12.056.1. I want to setup a dhcp server and wonder how should I config it? All the hosts in the network using the same net-mask and gateway.
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May 6, 2011
I have a 6to4 tunnel running on Ethernet (subnet 2002:ad4c:16cc:1) without problem. It runs radvd and announces a default route back to the Internet like this: "default via fe80::6a7f:74ff:fe0a:fbec dev br0"
On this same Ethernet I have a Linux plugbox (fe80::225:31ff:fe01:cc) which is a gateway to a network of IPv6 enabled sensors. I've assigned this second subnet 2002:ad4c:16cc:2. How do I get the plugbox to announce "2002:ad4c:16cc:2 via fe80::225:31ff:fe01:cc" so that the hosts on the Ethernet (2002:ad4c:16cc:1) will automatically pick up the route? The route works if I add it to the boxes manually. I've tried getting radvd on the plugbox to do this but I've had no success.
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Jul 16, 2010
I am trying to configure dhcpd to provide two different pools of IPs- one for dynamically named hosts specific to MAC addresses, and another for everyone else.So, a machine with X MAC address connects, gets an IP from e pool, and the server updates DNS with the address under a specific hostname.For the other pool, it just assigns the IP, no DNS updates.The "class" function doesn't appear to allow anything but pattern matching, and I can't find anything that specifies what "allow" and "deny" options therere for the pool command.Here's my config so far - will this do what I want?
Code:
key dhcpd {
algorithm hmac-md5;
[code]...
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Jul 22, 2011
I have TWO L3 + router switch (say switch1 and switch2). I created VLAN100 with VLAN ID 100 in both the switches. I created router 192.168.1.1/24 in Switch1. I created router 192.168.2.1/24 in Switch2. Switch1 is connected with 1.x/24 PCs. PCs are configured with 1.1 gateway. Switch2 is connected with 2.x/24 PCs. PCs are configured with 2.1 gateway. Both Switch1 and switch2 are connected by a trunk to carry VLAN100 data.
1)I have few PCs of 1.x connected to say Switch1 Is it possible for PC with IP 192.168.1.100(x) to ping PC with IP 192.168.2.100(y)?What are the configuration required in both switches to make them communicate ? All the device in both the subnets should ping/communicate with each other.
2)Move PC (192.168.1.100) to switch2. Move PC (192.168.2.100)to switch1.What will happen when PC(1.100) ping (2.100) and vice versa?What will happen when PC(say 1.80 in switch1) pings PC (say 1.100 in switch2) and vice versa? What will happen when PC(say 1.80 in switch1) pings PC (say 2.100 in switch1) and vice versa?
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Jan 12, 2011
My company hosts five Servers with CentOS 5 installed in a Data Center. The Data Center assigns a VLAN to each customer so that they can organize customers and also count traffic. The VLAN assigned to my company is in the form 62.103.X.X with a subnet mask 255.255.255.240 so the IPs that we can use in our Servers are 13. The first IP in the VLAN (for example 62.103.1.1) is the Gateway and the rest, that are calculated from the subnet mask, are assigned to servers(62.103.1.2 up to 62.103.1.14).
The problem I have is that we have run out of IPs in our VLAN. We have used all IPs and we want some more. The Data Center can assign new IPs but not grow our VLAN IPs by expanding the subnet mask. So they gave us a new VLAN with some IPs (for example 62.104.X.X with a subnet mask 255.255.255.192) They told me that I had to use as gateway the gateway of the first VLAN 62.103.1.1 and assign the new IPs as usual. So I assigned to one of the CentOS 5 servers the IP 62.104.1.2 and set the gateway to 62.103.1.1. Unfortunately this did not work and we could not establish connectivity to the Internet.Is it possible to assign a gateway outside of the IPs that are in the subnet? Could it be a problem with the VLAN setup by the Data Center?
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Jul 4, 2011
I installed Redhat Enterprise linux server5. it has two LAN card and two subnet connected to these two LAN card. i can browse network from these two network easily. But i created VLAN on one network card.Now i cant browse network from these VLAN subnet.
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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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Jul 26, 2011
I am using centOS 5.0. After I change from DHCP to static IP address, I cannot ping hosts on the same subnet. The error message says destination host unreachable. Before I made the changes I was able to ping and now even I change it back to DHCP I still cannot ping with the same destination host unreachable message. The centOS is running on VMware on a Windows host.
ifconfig shows
eth0 Link encap:Ethernet HWaddr 00:0C29:A1:9A:10
inet addr: 192.168.0.202 Bcast:192.168.0.255 Mask: 255.255.255.0
inet6 addr ......
After pinging 192.168.0.106 (106 is on and other host can ping it), arp -a shows ? (192.168.0.106) at <incomplete> on eth0 I tried different ways by disabling the firewall and and disabling SE protection. No Luck.
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Aug 6, 2010
I will try to explain a bit first about my network typology: I have one cent os 5.5 machine with 2 nics - external one 86.x.x.122 and internal one with 2 IPs: 192.168.1.1 and 89.x.x.121. The ideea is that I have a public subnet (86.x.x.120/29) of IPs which are routable only through 86.x.x.122 so I have a webserver hosted on a different machine with the IP of 89.x.x.122 and GW 89.x.x.121 - everything works perfectly fine, except that I cannot access from the internal network 192.168.1.0 / 24 the so called DMZ (roughly) - the 89.x.x.122.
What really makes me crazy is that I setup the IPtables rules correctly because I can access the webserver from the outside world but I cannot accessit from the internal network...
what I'm missing - why the 192.168.1.0/24 cannot see the 89.x.x.122 machine... What IPtables rules should I add?
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Oct 24, 2010
I've got a bit of a question. My network is laid out like this:
The role assignments are thus:
Firewall - sorts out the passing through to the 3 different networks, and acts as the traffic proxy.
Windows 2003 server - Does Active Directory and DNS
CentOS server - FTP and DHCP
Now, my problem is I need the CentOS server to be able to assign IP address to both networks, however, the CentOS server can *ONLY* be connected via the one interface to the firewall. It needs to assign the Windows 2003 server and the eth0 of the firewall an IP address via static DHCP, but it also needs to able to assign the clients dynamically via any address in the 10.23.1.0/24 range. I was thinking that I would be able to create static only assignments for the servers via their MAC addresses, and only have 1 dynamically assignable entry for the clients, and then get the firewall to allow ports 67 and 68 to flow freely between eth0 and eth1, but I wasn't entirely sure of the best way to do all this.
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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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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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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 28, 2009
I am trying to install CentOS 5.4 64-bit on a server with two NICs, one of which allows for iSCSI boot. I want the NIC that allows for iSCSI boot to connect to the iSCSI target on my 169.254 subnet. I want the other NIC to be connected to my 192.168.1 subnet so that it can reach the Internet for the CentOS Network Install.
Anaconda only configures one NIC, leaving me with an iSCSI target and no Internet or with Internet and no iSCSI target. Is it possible to configure both NICs in Anaconda?
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Jan 7, 2011
I have two NICs and both having different IPs and Default Gateways. Now CentOS by default picks only one default gateway and puts entry in routing table (route -n). I want to keep both default gateway in active mode to achieve redundancy. For example if traffic enters through eth0 then it goes out using default gateway of eth0 and if traffic enters from eth1 then it goes out using default gateway of eth1. I use command route add default gw 192.168.0.1 netmask 0.0.0.0 dev eth2 then both default gateways becomes active. Now I want to make sure that when server reboots both default gateways are setup. For this I wrote shell script/sbin/route add default gw 192.168.0.1 netmask 0.0.0.0 dev eth0/sbin/route add default gw 192.168.0.10 netmask 0.0.0.0 dev eth1I am calling this script via /etc/rc.local but it doesn't work on boot time however once server is booted and I execute script (sh script.sh) then it works fine.
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Jun 14, 2011
I just installed CentOS 5.2 on a mini Atom server and it wont recognize the nics. Not sure what kind they are, think they are Intel. (built in)It's the first time this has happened to me. Where do I start to get it to recognize the nics? Normally it works out of the box.
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Apr 1, 2011
I had a server that I use for Radius DNS and Trying to put DHCP on it I have My pool in it seems right. I have 2 adresses aliased one being a helper IP that the router will send the request to. When I try to start the dhcp server I get the following.
Mar 31 14:33:11 rad2 dhcpd: No subnet declaration for eth0 (76.164.173.2).
Mar 31 14:33:11 rad2 dhcpd: ** Ignoring requests on eth0. If this is not what
Mar 31 14:33:11 rad2 dhcpd: you want, please write a subnet declaration
Mar 31 14:33:11 rad2 dhcpd: in your dhcpd.conf file for the network segment
Mar 31 14:33:11 rad2 dhcpd: to which interface eth0 is attached. **
[Code]...
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Apr 4, 2010
I have a whitebox server with three network adapters, two gigabit adapters using the intel 82573V chips, and an intel pro/100 adapter based on the 82562 chip. These are embedded on an MSI motherboard. None are passing traffic.I initially booted the box using a Knoppix 5.0.1 CD, and the NICs worked fine. When I installed CentOS 5.4, no joy.Interestingly, Intel recommends the e1000e driver (which I am using), but the Knoppix CD used the e1000 driver. Anyway, I pulled an updated e1000e driver from elrepo,installed it, and verified that it was in use with 'ethtool --driver eth2', and the correct driver/version was displayed.
Symptoms are no traffic passes, rx/tx packet counts in ifconfig are both 0 (no errors, either). Routing table looks fine; three routes: one for 169.x.x.x, 172.16.x.x (my subnet), and one for 0.0.0.0, all destined for eth2, and all up. When I ping 127.0.0.1, and the local adapter address, I get good replies. As soon as I ping a remote host on my subnet, I get 'Destination host unreachable'. Now, at one point, I actually got it to work. I applied a small patch from Intel to change a value in the EEPROM, rebooted as instructed, and the adapter came up and passed traffic. I did a 'yum update' to update my packages, and shortly thereafter, everything stopped working again.
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Jan 7, 2010
Running CentOS 5.4 x64. Have successfully bridged eth2 with br2 by following the instructions here: [URL]../Networking (under the RHEL section) Have been running several KVM VMs successfully via this bridge.
I am now trying to bridge additional interfaces by using the same routine. Each bridge is named to correspond with the ethX device its bridged with.
Example of ifcfg-eth0 script:
DEVICE=eth0
HWADDR=00:16:76:D6:C9:45
ONBOOT=yes
BRIDGE=br0
[Code]...
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Dec 22, 2010
I have a virtual machine with two network interfaces. Now I wanted that both are part of different domains and tried to configure that with system-config-network. But there I only could change the the domain for the entire system. Is it possbile to edit the Domain for each network interface. If yes how?
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