Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

There are two hosts, A and B, in different locations, and they are connected to the internet; for the following cases, is it possible that:

  1. B can receive packets from A, but A can't receive packets from B
  2. A and B can't reach each other, but both can receive or send packets to some other nodes successfully
share|improve this question

closed as not a real question by Breakthrough, Ƭᴇcʜιᴇ007, soandos, Journeyman Geek, mpy Jun 24 '13 at 17:53

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

2 Answers 2

up vote 3 down vote accepted

Yes, it's possible in various ways, mostly routing errors or deliberately setting routes on the hosts to send traffic for the other host to somewhere that doesn't exist.

It can also be forcibly achieved by putting firewalls in the way and configuring them to block some of the traffic.

1) Could happen accidentally with routing mistakes - outgoing and return traffic can have different paths, so it's possible A has a route to B that works, and B has a route to A that goes into a faulty or misconfigured device somewhere along the way and the traffic is lost. I saw this happen at work this week.

2) This could happen accidentally if the next-hop devices have poor configuration, but it's a bit of a contrived situation. e.g.

A is on 1.0.0.2/24, gateway: 1.0.0.1

B is on 1.0.2.2/24, gateway: 1.0.2.1

but the gateways are set as 1.0.0.1/16 and 1.0.2.1/16. So each host is configured fine, but each gateway won't send traffic destined for the other host out to the internet, because it thinks the host should be local. But both A and B can access most of the rest of the internet - just losing access to 1.0.x.x sites.

Edit: this appears to be about the same as your other question here: for a pair of hosts on Internet, are the routes the same in two directions?

share|improve this answer

Just add an appropiately configured firewall in between. Can even add C that can reach both even though they don't reach each other.

share|improve this answer

Not the answer you're looking for? Browse other questions tagged or ask your own question.