Am 04.03.2015 um 16:17 schrieb Jim Thompson:
> LRO works by aggregating multiple incoming packets from a single
> stream into a larger buffer before they are passed higher up the
> networking stack, thus reducing the number of packets that have to be
> processed.
> 
> LRO should not be used on machines acting as routers, (and it is
> quite likely that you’re using pfSense as a router or, equivalently,
> a router), as it breaks the end-to-end principle and can
> significantly impact performance.
> 
> TSO is similar, but for sending.  It works by queuing up large
> buffers and letting the network interface card (NIC) split them into
> separate packets just before transmit.
> 
> Both LRO and TSO can help if you are an endpoint, *not a router*.
> If you were using pfSense an an appliance (say, for DNS), they would
> possibly help performance.
> 
> Now onto “hardware checksum offload”:
> 
> First, let’s briefly discuss where checksumming is used.
> 
> The Ethernet hardware calculates the Ethernet CRC32 checksum and the
> receive engine validates this checksum. If the received checksum is
> wrong pfSense won’t even see the packet, as the Ethernet hardware
> internally throws away the packet.  (There are exceptions, such as if
> the interface is in promiscuous mode.)
> 
> Higher level checksums are “traditionally” calculated by the protocol
> implementation and the completed packet is then handed over to the
> hardware.  Recent network hardware can perform the IP checksum
> calculation, also known as checksum offloading. The network driver
> won’t calculate the checksum itself but will simply hand over an
> empty (zero or garbage filled) checksum field to the hardware.
> 
> Some cards will additionally process TCP and UDP checksums, as above,
> this isn’t going to be of any value on a router.
> 
> It’s possible, if everything else is right, then IP checksum offload
> can provide a modest performance improvement, but this is unlikely to
> be more than “noticeable” at the speeds where most individuals run
> pfSense.   However, at 10Gbps (or above), these engines become quite
> useful.   Support for these is an important component of our “3.0”
> effort.
> 
> In case it’s not clear by now, these settings are all *disabled* by
> default in pfSense.

This good explanation should find a way into the wiki!

Jens
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