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 _______________________________________________ pfSense mailing list https://lists.pfsense.org/mailman/listinfo/list Support the project with Gold! https://pfsense.org/gold