![]() ( src is the preferred source address, which will be used as the source address for non-replying traffics with the corresponding destination when you are not specifying one, e.g. Local 127.0.0.1 dev lo proto kernel scope host src 127.0.0.1 It appears to cause a difference for certain broadcast destination though, like 255.255.255.255, probably because it is used to determine the broadcasting link/domain in such case.) $ ip r show table local type local In the unicast case the specified interface of a local route does not seem to matter. Those routes determine what addresses you can bind/use as source address and what traffics will be "trapped" in the host itself (instead of actually being sent / forwarded out to another host). We can do so using NAT (Network Address Translation) table of the firewall.All of the combiantions could be used for a loopback test, at least in Linux, since in what cases will loopback occur pretty much entirely depends on the type local routes in the route table local (ID 255). destination machine can directly find this out if it try to trace the incoming packets using tshark/ wireshark like tools. ![]() What this means is, we will indeed be using valid IP address of our machine to communicate with destination, but this all will happen under the hood! P.S. Having said that, in the case above to work ping -I (lookback) (destination) we can configure the firewall to transfer the requests generated by the lookback IP to be masqurade so as to change the source IP with the valid eth0 IP. as Lister maintained lookback IP is used by the device to talk to itself for self-diagnostics and trouble shooting. related discriptionĬan we actually use lookback IP to connect with other network machine? ![]() It is used mainly for diagnostics and troubleshooting, and to connect to servers running on the local machine. The loopback device is a special, virtual network interface that your computer uses to communicate with itself. We can not use lookback IP to communicate with the outside network! BUT. If you do send a packet from that ip, it will be ignored by other devices. If you have no gateway, or the gateway does not know where the network is, then the message is not sent.ġ27.0.0.1 is always on a different subnet to your network, routing devices will never route traffic from it, and your host machines will not try to send messages from it. A message will be sent to the gateway and the devices rely on the gateway to send over the message. However, if I have 192.168.0.1 ping 192.168.1.1, they will again look at the network portion and see it is different. If I try and ping 192.168.0.1 from 192.168.0.2 They will look at their subnet and identify their network portion of the ip address (192.168.0) They both see they are on the same subnet, and communicate. ![]() Lets assume your network is on the 192.168.0.0 subnet with the subnet mask of 255.255.255.0. If they are, they will talk, if not, they will attempt to use a gateway (router etc) to try and get there. When computers talk, they check to see if they are on the same subnet as the device they are talking to. If you ping 127.3.3.3 for example your device will ping itself. Local loopback uses the ip range 127.0.0.1-127.255.255.254Ī loopback device is generally assigned that entire range. I thought I would give a full answer to follow up on the comments.
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