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Fidel
Asked: 2016-07-05 12:51:32 +0800 CST

Traffic is routed via unknown means

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I have 2 machines running CentOS:

Machine A has two NICs: 192.168.150.1/255.255.255.0 and 192.168.1.1/255.255.255.0
Machine B has one NIC:  192.168.150.2/255.255.255.0

Machine B is connected directly to A (NIC to NIC), and has a route defined:

Destination     Gateway           Genmask
192.168.1.0     192.168.150.1     255.255.255.0

On machine A, sshd is bound to 192.168.1.1. However it's possible to ssh into 192.168.1.1 from machine B. Why could that be the case?

TCP forwarding is not enabled on Machine A. Also, machine B does not have an SSH ProxyCommand defined. Is there some other way that traffic received on 192.168.150.1 is being routed to 192.168.1.1?

centos ssh iptables route

1 Answers

  1. Linux uses the strong end system model. IP addresses do not act in a way as if they were different machines. Instead a machine acts like it owns all its IP addresses.

    Since 192.168.150.1 and 192.168.1.1 are the same machine, no forwarding or routing is needed. If you reach one, you've reached the other.

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