... say for CentOS?
From what I understand a virtul IP can let you abstract the address from the physical interface(s) the traffic actually goes through. If your server has two network cards it can have a single virtual IP and have the traffic go through either network physical interface. If hardware failure occurs on one of the two network cards, the traffic can keep going with the second one as a backup. I assume that this is more relevant on servers where such parts can be hotswapped.
A Virtual IP address is a secondary IP set on a host, it's just another IP bound to an adapter (adapters if bonded). This IP is useful for many things but most commonly used for webservers to run multiple SSL certificates for multiple sites.
In CentOS you pretty much copy the /etc/sysconfig/network-scripts/ifcfg-eth0 (whichever for the adapter you want) to /etc/sysconfig/network-scripts/ifcfg-eth0:1, In there change the devicename=eth0 to devicename=eth0:1 and change the IP for the new "virtual IP" you want.
Check out this article on Virtual IP address. As indicated it usually floats between machines, and is sometimes used to fail-over a service from one device to another. Are you thinking of a virtual interface instead perhaps?
/Allan
Related
I have an embedded webserver running on a device. Now I want a smartphone app to connect to the webserver. They are on the same wifi network but they don't know each others IP addresses.
I understand that this problem is often solved by implementing the mDNS protocol on the server. But are there any alternatives? Can the server maybe ask for specific IP address or similar?
If it has to be entirely automated, such that the embedded webserver is discoverable, perhaps scan the entire netblock looking for the correct response "http://[IP_address]/yes-im-the-one" from your embedded webserver?
Although beware, some network monitors may then consider the IP of your smartphone/device that does that scan "dangerous" and cut it off from the network - this is probably only a "big enterprise" problem.
...after you "find" your server, perhaps the application should cache/remember this, so it doesn't have to scan next time.
Other things you could do: give your embedded webserver a static IP on the LAN, either by setting this on the device itself, or via a DHCP reservation from whatever is the local DHCP server on the LAN.
What allot of emended devices do is come delivered with a static LAN IP already set on it, then it's up to the sysadmin to change their computer's IP temporarily to be in the same range, then they can visit the webserver or telnet into the default IP, and change it to what they want (to match their network's IP range)
If I run socket.gethostbyaddr(ip) in Python for example, I can get back the host name of the device with the specified IP address.
I understand that large networks have internal DNS servers to keep track of the IP host pairings, but how is this task accomplished on small home networks without an internal DNS server?
If you are trying to resolve names for hosts on your LAN, you may choose to populate your hosts file (/etc/hosts on typical *nix systems) with static entries for your local hosts. Generally, by default, the resolver consults the hosts file before going out to the DNS servers provided by your ISP.
If the hosts on your LAN are themselves using dynamic addressing through DHCP for address assignment, then you are facing a more dicey solution. I tend to stick with static addressing on my house LAN for just this reason.
I have two applications (diy container type) which have to be connected via TCP. Let's take as example application clusternode1 and clusternode2.
Each one has TCP listener set up for $OPENSHIFT_DIY_IP:$OPENSHIFT_DIY_PORT.
For some reason clusternode1 fails to connect to any of the following options for clusternode2:
$OPENSHIFT_DIY_IP:$OPENSHIFT_DIY_PORT
$OPENSHIFT_APP_DNS
Can you please help in understanding what should be url for external TCP connection?
You might check the logs to see if the OPENSHIFT_DIY_IP for both apps are within the same subnet. If one, say, is...
1.2.3.4
...and the other is...
1.5.6.7
...for example, then you might not expect Amazon's firewalls to just arbitrarily allow TCP traffic from one subnet to another. If this were allowed by default then one person's app might try to hack another's.
I know that when you're dealing directly with Amazon AWS and you spin up multiple virtual servers you have to create virtual zones to allow traffic between them. This might be something that's necessary.
Proxy Ports I don't know if this is useful but it's possible that a private IP address is being bound to your application(s) and then a NAT server is translating that into a public IP address.
can one location have more than 1 IP address? I have 2 IP addresses and need to know if they originate from the same source. Thanks
You're missing clear definitions of "location" and "source" in your question but lets go with the assumption that you mean "physical machine" for both (as it's obvious that multiple machines will have different addresses and that a single machine can change its IP address over time).
In that case, the answer is yes. The operating system may bind as many IP addresses to a physical network port (and a single MAC -- the physical addressing used by Ethernet) as it wishes.
Binding multiple IP addresses was the standard way of doing "virtual web hosting" before HTTP/1.1 arrived with the "Host" header. The provider would use DNS to map different host names to different IPs on the same network (usually the same subnet as well) and then assign all of them to the same interface. The webserver would get address information from an incoming connection and based on the local IP address would know which virtual host was being accessed.
This led to a higher-than-typical use of public IP addresses but the practice is now gone with the proliferation of HTTP/1.1.
I'm not sure how Windows presents it, but Linux will present a physical interface with multiple IP addresses as multiple logical interfaces such as "eth0", "eth0:1", "eth0:2", etc. Each logical interface has a unique IP address even though they share the same physical interface.
This is hard to tell. Especially it is hard to tell if these IP addresses are from different times. Today I may have a different IP address than tomorrow.
Even they are from the same time, a load balancer im my internal equipment might send my packets over the fail-over line if the 1st one is overloaded or broken down.
One network adapter normally has only one IP address at once and a typical end user only has one network connection active, but even then the IP address can change. The user could switch from wireless to wired and back or a power outage might reset the ISP's DHCP server (assigning everyone a new IP address).
If you want to identify the user even if his IP address changes, you need to identify the user by his session id, stored in cookies. As two users can have the same IP address (a whole company could be behind a NAT), you should never rely on IP addresses for identification.
So, my work has several networks and small business locations all with an internet blocking server. The managers all rotate and want freedom from the server, AKA static IP addresses outside the range of DHCP.
my problem is that they all need access to each others network, so setting up an alternate configuration is not that useful. How would I create an application that will change my users IP Address so that it will match their static IP at the location they changed it too?
This is just their internal IP address on their local machine, and each location's network has a static ip waiting for them. Just have to change their IP Address.
Is there a batch file command that can help achieve this? if not maybe writing a script or going into a larger application?
Doing this on the machine itself will be difficult. It needs to be able to recognise each network, and what will it do when connecting to an unknown network like a home network or a hotspot?
I think it would be better to let the DHCP server hand out static addresses from outside the normal dynamic address pool. That way everything keeps working automatically while also giving static addresses to the machines.
I know this is not a real answer to your question, but I hope this gives you an alternative.