- #ISTAT MENUS DAEMON BERKELEY PACKET FILTER UPDATE#
- #ISTAT MENUS DAEMON BERKELEY PACKET FILTER DRIVER#
- #ISTAT MENUS DAEMON BERKELEY PACKET FILTER SERIES#
Should a eBPF program require configuration or need to store information, maps are created and accessed via a special file-system. For example, changing addressing information at this point would require that the eBPF program execute a fib lookup to correctly populate address fields, fortunately there is a helper for that. At this point, an eBPF program could change the skb and those changes would be reflected in the packet on the wire, potentially resulting in an invalid packet as Linux has already completed its checks. The TC egress hook is at the end of Linux processing and the skb has been updated to send the packet. Linux forwarding has a number of checks to ensure that the packet came from a valid source, modifying addressing information incorrectly will result in those tests failing and Linux discarding the packet, silently unless martian notification is enabled. In the case of the ingress TC, the next step is Linux forwarding where a forwarding table (fib) lookup is done.
The Linux stack will expect to receive a correctly formatted packet or metadata to continue to move the packet through the system. Of course updating fields in the packet will change how Linux processes the packet.Īt the XDP or TC ingress hook, if the action is set to OK, the packet will be forwarded through the Linux stack. The action at the end of the program or programs can either forward to the next part of the Linux stack as if nothing happened or discard it.
#ISTAT MENUS DAEMON BERKELEY PACKET FILTER UPDATE#
Conceptually, at a tc hook a helper is used to copy the skb fields that are needed by the program from the packet, the execution logic runs, a helper is used to update the skb, and the skb then continues on its way. The loaded eBPF program is triggered by the receipt of a packet, and that packet is processed by the program.
#ISTAT MENUS DAEMON BERKELEY PACKET FILTER SERIES#
eBPF has a series of helper functions that are used to interact with the data and the linux networking stack. The egress hook is at the end of Linux networking before the packet is constructed and sent to the driver. The tcpdump tool attaches at the same place. The traffic control ingress hook is immediately after Linux has created the “skb” metadata. The Linux stack has not yet processed the packet, XDP programs operate directly on the packet data.
#ISTAT MENUS DAEMON BERKELEY PACKET FILTER DRIVER#
The eXpress Data Path hook is the earliest possible point in software, where the network driver receives the packet. Linux networking has three hooks where eBPF programs can be attached: If the packet is destined to be forwarded, the metadata contains the packet header information at the egress interface where the packet is constructed by retrieving the payload from memory and combined with the metadata.
When a packet arrives, the payload data is put into memory and metadata (referred to as “skb”) is created from the packet headers and then manipulated to achieve the forwarding desired. Linux provides routing functionality and works in a similar manner to a router. Although you may not know it, you are already familiar with these hooks, because functions such as IPtables and tcpdump use them. Using eBPF a small program running in a protected manner can be inserted at each of those hooks. At each of these hooks, information related to that hook is available. The Linux Kernel has “hooks” where functionality can be added. We will focus on eBPF for networking, however the technology has many other uses. Here we will try to split the difference and provide a high level view in an effort to assemble the jigsaw. There is lots of marketing material from companies using it to offer many different solutions and a lesser amount of terse technical material. Confused by Enhanced Berkeley Packet Filters, understandably so.
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