I have recently run into a discussion on this topic, and I think there is a need for some more detailed technical answer.

I want to ask this simple and basic question:

When I configure a service on an IP network host (http, ftp, dns, etc.), e.g. and I access the service from the same host with the IP address of one network interface (not with - loopback, but, is there any chance that the IP packets with the sourceIP=destinationIP= get anywhere beyond the local network interface?

(So when there is a problem with the switch or router it could cause my service (dns ...) to become unavailable from a browser running on


There might arise a challenge not from the packet itself -- as you ask in your question -- but from additional requests that the webserver starts in order to start-up (see this Apache page) or even worse to deliver each single response. The problem is based on a reverse DNS lookup. So, when your host is disconnected this might lead to a bad or no service ... caused by the webserver waiting for a DNS timeout or rejecting replies when the lookup cannot be done.

  • Thanks, but I am not interested about what a particular service does internally, so assume, that the question is about a service, that works per response/request only, like DNS for locally defined zone. – Vojtěch Dohnal Jun 6 '16 at 16:40

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