Filtering

Alveo X3522 User Guide (UG1523)

Document ID
UG1523
Release Date
2023-08-25
Revision
1.4 English

The X3522 adapter has simpler hardware receive queue selection (filtering) than its predecessors. This simplification together with the shared receive queue architecture means applications need to perform a level of filtering when inspecting received packets. Note the Onload and TCPDirect libraries handle this application level filtering on behalf of any software they accelerate, and therefore the user software does not need to change.

The hardware filtering supports matching on local IP address/port/protocol, or on MAC address+VLAN at a lower precedence. It can direct matched packets to a particular receive queue or drop them. The hardware supports up to 512 filters per port, implemented using a high performance hardware CAM.

The hardware only actions a single filter, even if subsequent filters would also match the packet. There is no hardware replication of packets to deliver to multiple queues. The software stack has mechanisms so that applications wanting the same packets can discover and share a filter and its associated traffic.

Multicast Filtering

The X3522 should identify multicast packets by their IP address, whereas its predecessors typically did so by MAC address. The X3522 adapter supports a multicast-mismatch filter to redirect or drop multicast traffic that does not match a more specific filter. This is the lowest precedence filter.

If an accelerated application installs a multicast-mismatch filter with drop rule, the net driver will then not receive intended multicast traffic. The application can avoid this issue by installing filters to direct all desired multicast traffic to its receive queue. These filters will always have a higher precedence than any multicast-mismatch drop filter.