Hello,
I have 2 subnets,
A and
B and a router connected to both
A and
B and the WAN.
I have 4 servers dual homed on subnets
A and B, 2 of them are Mac OS and 2 of them are Centos 7 (1503). They are all configured to reply on the same interface that requests were received and the gateway on the
B subnet is their default gateway. This
diagram shows the network.
The 2 Mac OS servers and one of the CentOS servers,
Bob, work fine in that each can ping and ssh into the others via their subnet
A or
B addresses.
Additionally, clients on subnet
A can also access the Mac OS servers and the CentOS server,
Bob via their subnet
A or
B addresses; and the three servers can access any of the clients on subnet A.
The second CentOS server,
Alice, is the problem.
None of the other dual-homed servers or clients on subnet
A can ping or ssh into
Alice using
Alice's subnet
A address. Pings and ssh simply hang and I see no evidence of traffic at
Alice via tcpdump. The arp tables on the other servers and clients all show that
Alice's IP addresses on subnets
A and
B are mapped to the appropriate MAC addresses.
None of the other dual-homed servers can ping or ssh into
Alice using
Alice's subnet
B address.
However, clients on subnet
A are able to ping and ssh into
Alice by using
Alice's address on subnet B.
Further,
Alice can ping and ssh into all servers and clients via subnet A; and can ping the other three servers on subnet B, but when
Alice attempts to ssh into any of the servers via their subnet
B addresses,
Alice receives "Connection refused"?!
The servers
Bob and
Alice are intended to be configured the same except of course for addresses.
I've compared the various
/etc/sysconfig/network-scripts/{ifcfg-, route-, rule-}{eno1, eno2} on
Bob and
Alice and they appear to be identical except for the addresses assigned to each interface.
I've compared "ip addr", "ip route", "ip rule" between
Bob and
Alice and all look identical save for address assignments.
I have disabled SELinux and disabled the firewall on
Alice to remove these from consideration.
I'm befuddled regarding where the misconfiguration on
Alice is.
It seems to me from the evidence that there is not
A hardware problem with either of
Alice's interfaces since I can reach each interface from the router via the subnet
A and
B addresses for
Alice and clients on subnet
A can reach
Alice via the subnet
B address.
It doesn't seem to be
A problem in the router since all other combinations of communication are working.
Further, the connection refused doesn't seem to be
A configuration issue with the other three servers via subnet
B since they are all able to connect to each other on subnet B. From looking at tcpdump when
Alice tries to connect to the other three servers on subnet B, I don't see any packets arriving at the
B interfaces on the other three servers.
I would really appreciate any ideas about where to probe to try and resolve this issue.
Thank you,
Chris
