Linux server (VM) networking confusion

[shannonadams]

itadmin is a current physical server and it can ping everything on our 10.x.x.x network.

itadmin2

is a virtual machine that is setup like just itadmin except for different IP

addresses and hostname. itadmin2 can ping 10.9.xx.xxx (such as 10.9.10.203),

but cannot ping 10.9.xxx.xxx (such as 10.9.110.200), or anything

outside 10.9. (10.10.10.205), or Internet sites ([www.cnn.com|http://www.cnn.com/]).

Both

are running Linux FC4. Furthermore, you can ping 10.9.10.251 from

10.9.xx.xxx (such as 10.9.10.203), but cannot ping it from 10.9.xxx.xxx

(such as 10.9.110.200).

My plan is to migrate off itadmin onto itadmin2, but I think this is the last obstacle keeping me from doing that.

10.9.10.202 (itadmin)

eth0 inet addr:10.9.10.202 Bcast:10.9.10.255 Mask:255.255.255.0

eth1 inet addr:10.9.112.202 Bcast:10.9.112.255 Mask:255.255.255.0

10.9.10.251 (itadmin2)

eth0 inet addr:10.9.10.251 Bcast:10.9.10.255 Mask:255.255.255.0

eth1 inet addr:10.9.112.251 Bcast:10.9.112.255 Mask:255.255.255.0

Regarding DNS setup - our inside DNS server address is 10.9.10.190 and outside is 10.9.10.191

itadmin's resolv.conf is:

search bigrocksports.com

nameserver 10.9.10.193

nameserver 10.9.10.191

itadmin2's resolv.conf is:

search bigrocksports.com

nameserver 10.9.10.190

nameserver 10.9.10.191

Any

ideas on what is going on? Why can't itadmin2 be reachable from all

devices on the 10.x.x.x network and be able to ping everything itadmin

can?

Thanks,

Shannon

[Chris_Howard]

Can you confirm that you can ping your dns servers and default gateway from itadmin2.

Also - if you run nslookup, are you able to query the dns servers?

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[shannonadams]

Thanks for the reply, Chris.

From itadmin2, I can ping both DNS servers (10.9.10.190 and .191) and the default gateway (10.9.10.1). I figured out a big problem. I could ping the gateway of eth0 (10.9.10.251); which is 10.9.10.1. However, I had the gateway set to 10.9.112.1 for eth1 (10.9.112.251) and could not ping that. Once I changed eth1 gateway address to 10.9.10.1, I could ping everything on our network and www.google.com, etc.

However, I am down to another strange issue (and hopefully the last). itadmin2 can ping our main production server - 10.9.110.200. But, 10.9.110.200 cannot ping itadmin2 (10.9.10.251 or 10.9.112.251). Any ideas?

Thanks,

Shannon

[adolopo]

What does "netstat -nr" spit out on each VM?

[shannonadams]

itadmin2 (VM - replica of itadmin physical)

# netstat -pr

Kernel IP routing table

Destination Gateway Genmask Flags MSS Window irtt Iface

10.9.10.0 * 255.255.255.0 U 0 0 0 eth0

10.9.112.0 * 255.255.255.0 U 0 0 0 eth1

169.254.0.0 * 255.255.0.0 U 0 0 0 eth1

default 10.9.10.1 0.0.0.0 UG 0 0 0 eth0

itadmin (physical server that is "reachable/pingable" from all servers:

# netstat -pr

Kernel IP routing table

Destination Gateway Genmask Flags MSS Window irtt Iface

10.9.10.0 * 255.255.255.0 U 0 0 0 eth0

10.9.112.0 * 255.255.255.0 U 0 0 0 eth1

169.254.0.0 * 255.255.0.0 U 0 0 0 eth1

default 10.9.10.1 0.0.0.0 UG 0 0 0 eth0

[Chris_Howard · Accepted solution]

From the information you have posted, 10.9.10.1 is not in the same subnet as eth1.

I assume there is no gateway/ router attached to subnet to which eth1 is connected.

..if so I would leave the default gateway blank for eth1.

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[kjb007]

Agreed. You can not have more than 1 default gateway. Set the default to be one of your interfaces, preferrably the one that is already set. Any other interface should not have any gateway assigned.

-KjB

[shannonadams]

Ok, that was it. I needed to leave the default gateway blank for eth1. Now, I can ping everything from itadmin2 and all network devices can ping itadmin2; except for consistently.. Any ideas? 10.9.110.200 has to be able to reach itadmin2 before I can turn the physical server off and have the VM/itadmin2 takeover.

Thanks for all the help,

Shannon

[Chris_Howard]

That's probably a question you need to ask your network guys.

The Solaris servers (10.9.110.200/ 10.9.110.220) are not on either of the 2 subnets your network cards are attached to - i.e. 10.9.10.x or 10.9.112.x

You may have a routing problem - the traceroute command may help to resolve this.

Can you confirm did your source server, itadmin, have a default gateway address set for the card with address 10.9.112.202?

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[shannonadams]

Chris, what command do I run to see the default gateway (if any) for the card with address 10.9.112.202? I ran ifconfig, but that doesn't list it.

[adolopo]

"netstat -nr"......the interface is listed on the far right, and the Destination IP you're going to want to zero in on is "10.9.112.0" <--the subnet.

I know...i'm not Chris. Sorry. 😃

[shannonadams]

Okay, here is

itadmin:

netstat -nr

Kernel IP routing table

Destination Gateway Genmask Flags MSS Window irtt Iface

10.9.10.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

10.9.112.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1

169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1

0.0.0.0 10.9.10.1 0.0.0.0 UG 0 0 0 eth0

itadmin2:

netstat -nr

Kernel IP routing table

Destination Gateway Genmask Flags MSS Window irtt Iface

10.9.10.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

10.9.112.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1

169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1

0.0.0.0 10.9.10.1 0.0.0.0 UG 0 0 0 eth0

[shannonadams]

This is getting strange. I haven't changed anything since blanking out the gateway address on eth1 on itadmin2. But now, I have been able to ping itadmin2 from the Solaris servers just fine for the past ten minutes. I will keep you posted...

[Chris_Howard]

Maybe a routing or arp cache update has happened on your router/ switch in the meantime.

Give it a couple of hours, and if it's still OK, you're probably sorted.

If you found this helpful please consider the use of the Helpful /Correct buttons to award points. Thanks !!

[shannonadams]

Thanks for all the help. I successfully migrated itadmin over to VM last night and it is running flawlessly today - finally!

Shannon