Recently, I focus on OpenStack things where an interesting network question comes out: If a host machine has multiple network interfaces, is it possible to ping all of them from another host?
To be clearer, we assume that Host A has a unique network interface
192.168.11.0/24, Host B has 2 interfaces:
Meanwhile, the 3 interfaces are connected by a router, as the graph illustrated.
If we look at the routing table of Host B, we’ll find something like
If we ping from Host B to Host A, Host B looks up its routing table and find
no specific rools for destination
192.168.11.0/24, so it will go via gateway
And if we ping from Host A to Host B of interface
192.168.125.0/24, it goes
well. However, if we ping to Host B‘s another interface, it will fail.
The reason is obvious, Host A send a packet to
192.168.126.92 and expect a
response from that destination. Unfortunately, Host B receives the packet but
can only response through
192.168.125.1, which will never match for Host A.
So in this case, the answer is NO. But if Host A‘s network interface is
192.168.126.0/24, it can ping the 2 interfaces of Host B, or if Host A
also has multiple network interfaces, with proper routing table setting, it can
ping both 2 interfaces of Host B as well.