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Let me start off with a network diagram to help everyone out:



Basically I am trying to get 172.16.0.0/24 to talk to 192.168.168.0/24 (but not the reverse). In order to do this I have set up the VM shown as Ubuntu 12.04 in the diagram as a router. It has two virtual NICs (each bound to a single physical NIC). One has an address for the 192.168.168.0/24 subnet and the other has an address for the 172.16.0.0/24 subnet. This automatically adds routes into the routing table for those destinations. I set my PXE clients to use a default gateway of 172.16.0.1 (the VM router), however I cannot ping or reach any of the 192.168.168.0/24 machines...

A traceroute reveals that the packet is reaching the gateway of 172.16.0.1 but then... nothing. Here's the bazaar thing: I enabled iptables and turned on masquerading for packets leaving eth0 (the 192.168.168.0/24 interface) AND THEN I was able to talk to 192.168.168.0/24... Why is this? I have never needed to enable that before - I thought the routing table should take care of it all...

I've set up many networks this way with a Linux box running in a VM doing the routing between the subnets...This one got me baffled.

Thanks in advance...

Edit: Doh. The 192.168.168.0/24 clients use a gateway that can't route back to 172.16.0.0/24. This is obviously the problem. And masquerading fixes this because the source address would then appear to be from 192.168.168.0/24...right?
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Ol' Sandy
(28 items)
 
"Zeus"
(12 items)
 
Elite Preview
(6 items)
 
CPUMotherboardGraphicsRAM
Intel Xeon E3-1230v3 Gigabyte GA-Z97X-UD5H-BK MSI Gaming GTX 980 Kingston 32GB (4x8) 
Hard DriveHard DriveHard DriveHard Drive
Plextor PX-256M5S 256GB Samsung EVO 1TB Hitachi HDS721010CLA332 Hitachi HDS723020BLA642 
Hard DriveHard DriveHard DriveOptical Drive
Hitachi HDS723020BLA642 Hitachi HUA722010CLA330 WDC WD10EARS-00Z5B1 TSSTcorp CDDVDW SH-S223B 
CoolingCoolingOSMonitor
Phanteks PH-TC14PE with TY-140's Lamptron FCv5 (x2) Windows 8 Pro 64-bit Dell U2412M 
MonitorMonitorMonitorKeyboard
Dell U2412M Dell U2212HM Dell U2713HM Topre Realforce 87UB | Ducky DK9087 G2 Pro 
PowerCaseMouseMouse Pad
Corsair AX-750 Corsair Obsidian 650D Logitech G700 XTRAC Ripper XXL 
AudioAudioAudioAudio
Beyerdynamic DT-770 Pro 250ohm Schiit Bifrost DAC Schiit Asgard 2 HiVi Swan M50W 2.1 
CPUMotherboardRAMHard Drive
Intel Xeon E5-2620 Super Micro X9SRL-F-B 128GB 1333MHz LSI 9271-8i 
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VMware ESXi 5.5 SeaSonic SS-400FL2 Fractal Define R3 
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