Hello,

I have a Linux LPAR which is supposed to be a router. It has 2 VIOS l-lans assigned which are actually 2 physical ports of a 4 port NIC. One is connected to the LAN and one to the WAN. Both are working fine if used on their own.

The troubles start when I use this LPAR for NAT. If I set it as the gateway on another box in the LAN I get 100kb/s tops. I tried lots of Linux settings but none helped.

At some point, just in case, I removed the l-lans from the LPAR and instead gave it its own, full, real NIC. And surprise, NAT speeds were fine instantly. So the VIOS NICs are the problem.

Is that a known limitation? Is it too much routing i.e. virtual NICs doing NAT?

Any insight would be welcome!

I figuered it out:

The network bridges need to have the large send option enabled which is off by default. After doing so the speed is fine instantly.