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Forum Discussion
Enable Jumbo Frames Causes External Hostname Problem
I use my ReadyNAS to host my web page. If I enable jumbo frames on my NAS and my PC then I can no longer access my web page using my external hostname (dyndns.org address) while on the LAN. I have to ...
When you are sending a jumbo packet via the external address, the ethernet packet is addressed to the router (having the router's mac address as the destination). So any pure layer-2 devices cannot tell that it is really for the NAS, and they will direct it to the router. This includes the built-in switch in the router itself. As far as that hardware is concerned, the destination is the router itself. So the packet is delivered to the router software, which then re-sends it back downstream to the NAS.
Not only does the router hardware need to support JF, the router software does as well.
This only applies to packets that are actually bigger than 1500 bytes, other packets should be delivered normally.
If you have a managed ethernet switch in between, you might be able to set it up to fragment JF packets on the switch-router link.
While I think I understand why jumbo frames can't be delivered, I am a bit puzzled as to why the PC and NAS IP stacks are trying to send them off-net in the first place (that is to the external IP). From their point of view the connection is being made over the internet, and as far as I can see, they shouldn't be attempting to use JF on that path. You might ask your friends about that.
What happens if you are really off-net (trying to access the NAS over the internet)?
Not only does the router hardware need to support JF, the router software does as well.
This only applies to packets that are actually bigger than 1500 bytes, other packets should be delivered normally.
If you have a managed ethernet switch in between, you might be able to set it up to fragment JF packets on the switch-router link.
While I think I understand why jumbo frames can't be delivered, I am a bit puzzled as to why the PC and NAS IP stacks are trying to send them off-net in the first place (that is to the external IP). From their point of view the connection is being made over the internet, and as far as I can see, they shouldn't be attempting to use JF on that path. You might ask your friends about that.
What happens if you are really off-net (trying to access the NAS over the internet)?
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