Member Avatar for SteveMunin

Hi... had a problem boggling the mind over the past few days and I'm about ready to pull my hair out, so I figured I would offer it up here to see if anyone had suggestions...

The Scenario:

Base server is running CentOS 3 with 4 different VMware machines configured on it. We use an IP tunneling solution through our ISP that allows us to lease small machines elsewhere and use the IP addresses on our local machines. Each VM is configured with a different set of IP addresses via bridged networking.

VM's 1, 2, and 3 are in perfect working order, however, VM 4 seems to be having a connection issue. When trying to bring up the IP range on this machine, the OS is reporting that they are up, however, the VM can't be pinged anywhere besides the host machine. I thought this may have been an issue with the tunnel, but found out that wasn't the case. I took the VM offline and tried binding the IP range to our main server, where they work fine. I unconfigured them again from the server, did a reset, and started the VM again to have no luck.

The server can ping the VM, but not the other way around (this gives me a "Destination Host Unreachable" error). Traceroute on the VM to any network gives me errors (the good ol' 3000 ms !H) ... netstat -rn looks normal to me.

I thought this may have been a gateway issue, but I'm sure that it's not, as I've been over the configuration files 100 times.

So with that... does anyone have any thoughts on this? Any help would be greatly appreciated!


Regards,
Steve

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  • Latest Post Latest Post by buzzburnz

Dani AI

Generated

Quick diagnostic checklist and likely causes based on the symptoms described by and the comments from and .

Start by capturing where the packet dies (run these on the VM and on the host while reproducing a ping/traceroute):

# on the VM: confirm address and route, then watch outgoing frames
ifconfig -a
route -n
tcpdump -n -i eth0 icmp or arp

# on the host: watch the VM bridge and the physical NIC
tcpdump -n -i vmnet0 icmp or arp
tcpdump -n -i eth0 icmp or arp
arp -an | grep <vm-ip>

What to look for and what it usually means

  • If you see the ICMP/ARP on the VM but not on the host physical NIC, the bridge/VMware side is not forwarding (bridge mapping, vmnet config or duplicate MAC is likely).
  • If you see the frames on the host NIC but get no replies, upstream (ISP tunnel or router) is dropping or has a stale ARP for that IP.
  • If the host can reach the VM but the VM cannot reach outside, check kernel filtering/routing on the host and edge behavior (reverse-path filter or FORWARD rules can drop replies).

Checks and quick fixes

  • Verify no MAC duplication across guests: check ifconfig -a on each VM and the host; cloned VMs often keep the same MAC.
  • Check kernel reverse-path filtering (common with tunneled IPs):
    cat /proc/sys/net/ipv4/conf/*/rp_filter
sysctl -w net.ipv4.conf.all.rp_filter=0
sysctl -w net.ipv4.conf.default.rp_filter=0
  • Ensure host firewall allows forwarding for that address range (inspect FORWARD chain and any bridge-nf settings).
  • If the ISP uses ARP/MAC binding for the leased addresses, ask them to clear the old entry or wait for the ARP to age; alternatively use proxy ARP on the host or route the block to the VM instead of bridging.

If those checks are inconclusive, create a minimal test VM with a fresh MAC and a single IP from the same block. If the test works, the problem is specific to VM4 (MAC, config, or firewall). If it fails, the issue is upstream or in the host bridging layer.

Recommended Answers

All 3 Replies

Member Avatar for jbennet

have you made sure that the virtual network adapter and VMWare network service are installed on the physical pc?

Member Avatar for SteveMunin

Everything is installed properly, yes. I have 3 other VM's on the same machine that are in perfect working order. I did think that maybe it was a problem with the bridged networking only allowing so many connections from the VM's, so I tried creating a second bridged adapter. This didn't work either.

-Steve

have you made sure that the virtual network adapter and VMWare network service are installed on the physical pc?

Member Avatar for buzzburnz

Did the CentOS firewall somehow mess you up in VM #4? Do an iptables -L and check to make sure that it didn't stick in something you didn't want.

Buzz

Hi... had a problem boggling the mind over the past few days and I'm about ready to pull my hair out, so I figured I would offer it up here to see if anyone had suggestions...

The Scenario:

Base server is running CentOS 3 with 4 different VMware machines configured on it. We use an IP tunneling solution through our ISP that allows us to lease small machines elsewhere and use the IP addresses on our local machines. Each VM is configured with a different set of IP addresses via bridged networking.

VM's 1, 2, and 3 are in perfect working order, however, VM 4 seems to be having a connection issue. When trying to bring up the IP range on this machine, the OS is reporting that they are up, however, the VM can't be pinged anywhere besides the host machine. I thought this may have been an issue with the tunnel, but found out that wasn't the case. I took the VM offline and tried binding the IP range to our main server, where they work fine. I unconfigured them again from the server, did a reset, and started the VM again to have no luck.

The server can ping the VM, but not the other way around (this gives me a "Destination Host Unreachable" error). Traceroute on the VM to any network gives me errors (the good ol' 3000 ms !H) ... netstat -rn looks normal to me.

I thought this may have been a gateway issue, but I'm sure that it's not, as I've been over the configuration files 100 times.

So with that... does anyone have any thoughts on this? Any help would be greatly appreciated!


Regards,
Steve

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