Opened 13 years ago
Last modified 10 years ago
#9440 closed defect
NAT networking rewrites the DF (dont fragment) flag — at Initial Version
| Reported by: | Oleg | Owned by: | |
|---|---|---|---|
| Component: | network/NAT | Version: | VirtualBox 4.1.0 |
| Keywords: | DF, fragmentation, dont fragment | Cc: | |
| Guest type: | Linux | Host type: | Windows |
Description
I found that NAT network removes, improperly, he IP packet DF flag (dont fragment) when the packet is crossing the boundary of the NAT networking. The bridged network works fine.
Environment:
VirtualBox 4.1.0 Host OS Windows 7 Guest OS Linux 2.6.38
Problem:
When we send a UDP packet (I tested only UDP) with DF flag set (0x02) in the IP header, to the "outside world", it appears on the wire outside of the NAT network as having the IP flags as 0 - the DF flag disappears.
The same is true on the receiving side: when the packet on the wire has 0x02 flag set in the IP header, it is getting delivered to the NAT network with flags 0.
When I am changing the networking settings to "bridged", everything works normally - the DF flag is preserved both ways. So, this is NAT-only problem, but rather annoying for some advanced applications which have to perform PMTU discovery, for example.
