| .. SPDX-License-Identifier: GPL-2.0 |
| |
| ============ |
| Devlink Trap |
| ============ |
| |
| Background |
| ========== |
| |
| Devices capable of offloading the kernel's datapath and perform functions such |
| as bridging and routing must also be able to send specific packets to the |
| kernel (i.e., the CPU) for processing. |
| |
| For example, a device acting as a multicast-aware bridge must be able to send |
| IGMP membership reports to the kernel for processing by the bridge module. |
| Without processing such packets, the bridge module could never populate its |
| MDB. |
| |
| As another example, consider a device acting as router which has received an IP |
| packet with a TTL of 1. Upon routing the packet the device must send it to the |
| kernel so that it will route it as well and generate an ICMP Time Exceeded |
| error datagram. Without letting the kernel route such packets itself, utilities |
| such as ``traceroute`` could never work. |
| |
| The fundamental ability of sending certain packets to the kernel for processing |
| is called "packet trapping". |
| |
| Overview |
| ======== |
| |
| The ``devlink-trap`` mechanism allows capable device drivers to register their |
| supported packet traps with ``devlink`` and report trapped packets to |
| ``devlink`` for further analysis. |
| |
| Upon receiving trapped packets, ``devlink`` will perform a per-trap packets and |
| bytes accounting and potentially report the packet to user space via a netlink |
| event along with all the provided metadata (e.g., trap reason, timestamp, input |
| port). This is especially useful for drop traps (see :ref:`Trap-Types`) |
| as it allows users to obtain further visibility into packet drops that would |
| otherwise be invisible. |
| |
| The following diagram provides a general overview of ``devlink-trap``:: |
| |
| Netlink event: Packet w/ metadata |
| Or a summary of recent drops |
| ^ |
| | |
| Userspace | |
| +---------------------------------------------------+ |
| Kernel | |
| | |
| +-------+--------+ |
| | | |
| | drop_monitor | |
| | | |
| +-------^--------+ |
| | |
| | Non-control traps |
| | |
| +----+----+ |
| | | Kernel's Rx path |
| | devlink | (non-drop traps) |
| | | |
| +----^----+ ^ |
| | | |
| +-----------+ |
| | |
| +-------+-------+ |
| | | |
| | Device driver | |
| | | |
| +-------^-------+ |
| Kernel | |
| +---------------------------------------------------+ |
| Hardware | |
| | Trapped packet |
| | |
| +--+---+ |
| | | |
| | ASIC | |
| | | |
| +------+ |
| |
| .. _Trap-Types: |
| |
| Trap Types |
| ========== |
| |
| The ``devlink-trap`` mechanism supports the following packet trap types: |
| |
| * ``drop``: Trapped packets were dropped by the underlying device. Packets |
| are only processed by ``devlink`` and not injected to the kernel's Rx path. |
| The trap action (see :ref:`Trap-Actions`) can be changed. |
| * ``exception``: Trapped packets were not forwarded as intended by the |
| underlying device due to an exception (e.g., TTL error, missing neighbour |
| entry) and trapped to the control plane for resolution. Packets are |
| processed by ``devlink`` and injected to the kernel's Rx path. Changing the |
| action of such traps is not allowed, as it can easily break the control |
| plane. |
| * ``control``: Trapped packets were trapped by the device because these are |
| control packets required for the correct functioning of the control plane. |
| For example, ARP request and IGMP query packets. Packets are injected to |
| the kernel's Rx path, but not reported to the kernel's drop monitor. |
| Changing the action of such traps is not allowed, as it can easily break |
| the control plane. |
| |
| .. _Trap-Actions: |
| |
| Trap Actions |
| ============ |
| |
| The ``devlink-trap`` mechanism supports the following packet trap actions: |
| |
| * ``trap``: The sole copy of the packet is sent to the CPU. |
| * ``drop``: The packet is dropped by the underlying device and a copy is not |
| sent to the CPU. |
| * ``mirror``: The packet is forwarded by the underlying device and a copy is |
| sent to the CPU. |
| |
| Generic Packet Traps |
| ==================== |
| |
| Generic packet traps are used to describe traps that trap well-defined packets |
| or packets that are trapped due to well-defined conditions (e.g., TTL error). |
| Such traps can be shared by multiple device drivers and their description must |
| be added to the following table: |
| |
| .. list-table:: List of Generic Packet Traps |
| :widths: 5 5 90 |
| |
| * - Name |
| - Type |
| - Description |
| * - ``source_mac_is_multicast`` |
| - ``drop`` |
| - Traps incoming packets that the device decided to drop because of a |
| multicast source MAC |
| * - ``vlan_tag_mismatch`` |
| - ``drop`` |
| - Traps incoming packets that the device decided to drop in case of VLAN |
| tag mismatch: The ingress bridge port is not configured with a PVID and |
| the packet is untagged or prio-tagged |
| * - ``ingress_vlan_filter`` |
| - ``drop`` |
| - Traps incoming packets that the device decided to drop in case they are |
| tagged with a VLAN that is not configured on the ingress bridge port |
| * - ``ingress_spanning_tree_filter`` |
| - ``drop`` |
| - Traps incoming packets that the device decided to drop in case the STP |
| state of the ingress bridge port is not "forwarding" |
| * - ``port_list_is_empty`` |
| - ``drop`` |
| - Traps packets that the device decided to drop in case they need to be |
| flooded (e.g., unknown unicast, unregistered multicast) and there are |
| no ports the packets should be flooded to |
| * - ``port_loopback_filter`` |
| - ``drop`` |
| - Traps packets that the device decided to drop in case after layer 2 |
| forwarding the only port from which they should be transmitted through |
| is the port from which they were received |
| * - ``blackhole_route`` |
| - ``drop`` |
| - Traps packets that the device decided to drop in case they hit a |
| blackhole route |
| * - ``ttl_value_is_too_small`` |
| - ``exception`` |
| - Traps unicast packets that should be forwarded by the device whose TTL |
| was decremented to 0 or less |
| * - ``tail_drop`` |
| - ``drop`` |
| - Traps packets that the device decided to drop because they could not be |
| enqueued to a transmission queue which is full |
| * - ``non_ip`` |
| - ``drop`` |
| - Traps packets that the device decided to drop because they need to |
| undergo a layer 3 lookup, but are not IP or MPLS packets |
| * - ``uc_dip_over_mc_dmac`` |
| - ``drop`` |
| - Traps packets that the device decided to drop because they need to be |
| routed and they have a unicast destination IP and a multicast destination |
| MAC |
| * - ``dip_is_loopback_address`` |
| - ``drop`` |
| - Traps packets that the device decided to drop because they need to be |
| routed and their destination IP is the loopback address (i.e., 127.0.0.0/8 |
| and ::1/128) |
| * - ``sip_is_mc`` |
| - ``drop`` |
| - Traps packets that the device decided to drop because they need to be |
| routed and their source IP is multicast (i.e., 224.0.0.0/8 and ff::/8) |
| * - ``sip_is_loopback_address`` |
| - ``drop`` |
| - Traps packets that the device decided to drop because they need to be |
| routed and their source IP is the loopback address (i.e., 127.0.0.0/8 and ::1/128) |
| * - ``ip_header_corrupted`` |
| - ``drop`` |
| - Traps packets that the device decided to drop because they need to be |
| routed and their IP header is corrupted: wrong checksum, wrong IP version |
| or too short Internet Header Length (IHL) |
| * - ``ipv4_sip_is_limited_bc`` |
| - ``drop`` |
| - Traps packets that the device decided to drop because they need to be |
| routed and their source IP is limited broadcast (i.e., 255.255.255.255/32) |
| * - ``ipv6_mc_dip_reserved_scope`` |
| - ``drop`` |
| - Traps IPv6 packets that the device decided to drop because they need to |
| be routed and their IPv6 multicast destination IP has a reserved scope |
| (i.e., ffx0::/16) |
| * - ``ipv6_mc_dip_interface_local_scope`` |
| - ``drop`` |
| - Traps IPv6 packets that the device decided to drop because they need to |
| be routed and their IPv6 multicast destination IP has an interface-local scope |
| (i.e., ffx1::/16) |
| * - ``mtu_value_is_too_small`` |
| - ``exception`` |
| - Traps packets that should have been routed by the device, but were bigger |
| than the MTU of the egress interface |
| * - ``unresolved_neigh`` |
| - ``exception`` |
| - Traps packets that did not have a matching IP neighbour after routing |
| * - ``mc_reverse_path_forwarding`` |
| - ``exception`` |
| - Traps multicast IP packets that failed reverse-path forwarding (RPF) |
| check during multicast routing |
| * - ``reject_route`` |
| - ``exception`` |
| - Traps packets that hit reject routes (i.e., "unreachable", "prohibit") |
| * - ``ipv4_lpm_miss`` |
| - ``exception`` |
| - Traps unicast IPv4 packets that did not match any route |
| * - ``ipv6_lpm_miss`` |
| - ``exception`` |
| - Traps unicast IPv6 packets that did not match any route |
| * - ``non_routable_packet`` |
| - ``drop`` |
| - Traps packets that the device decided to drop because they are not |
| supposed to be routed. For example, IGMP queries can be flooded by the |
| device in layer 2 and reach the router. Such packets should not be |
| routed and instead dropped |
| * - ``decap_error`` |
| - ``exception`` |
| - Traps NVE and IPinIP packets that the device decided to drop because of |
| failure during decapsulation (e.g., packet being too short, reserved |
| bits set in VXLAN header) |
| * - ``overlay_smac_is_mc`` |
| - ``drop`` |
| - Traps NVE packets that the device decided to drop because their overlay |
| source MAC is multicast |
| * - ``ingress_flow_action_drop`` |
| - ``drop`` |
| - Traps packets dropped during processing of ingress flow action drop |
| * - ``egress_flow_action_drop`` |
| - ``drop`` |
| - Traps packets dropped during processing of egress flow action drop |
| * - ``stp`` |
| - ``control`` |
| - Traps STP packets |
| * - ``lacp`` |
| - ``control`` |
| - Traps LACP packets |
| * - ``lldp`` |
| - ``control`` |
| - Traps LLDP packets |
| * - ``igmp_query`` |
| - ``control`` |
| - Traps IGMP Membership Query packets |
| * - ``igmp_v1_report`` |
| - ``control`` |
| - Traps IGMP Version 1 Membership Report packets |
| * - ``igmp_v2_report`` |
| - ``control`` |
| - Traps IGMP Version 2 Membership Report packets |
| * - ``igmp_v3_report`` |
| - ``control`` |
| - Traps IGMP Version 3 Membership Report packets |
| * - ``igmp_v2_leave`` |
| - ``control`` |
| - Traps IGMP Version 2 Leave Group packets |
| * - ``mld_query`` |
| - ``control`` |
| - Traps MLD Multicast Listener Query packets |
| * - ``mld_v1_report`` |
| - ``control`` |
| - Traps MLD Version 1 Multicast Listener Report packets |
| * - ``mld_v2_report`` |
| - ``control`` |
| - Traps MLD Version 2 Multicast Listener Report packets |
| * - ``mld_v1_done`` |
| - ``control`` |
| - Traps MLD Version 1 Multicast Listener Done packets |
| * - ``ipv4_dhcp`` |
| - ``control`` |
| - Traps IPv4 DHCP packets |
| * - ``ipv6_dhcp`` |
| - ``control`` |
| - Traps IPv6 DHCP packets |
| * - ``arp_request`` |
| - ``control`` |
| - Traps ARP request packets |
| * - ``arp_response`` |
| - ``control`` |
| - Traps ARP response packets |
| * - ``arp_overlay`` |
| - ``control`` |
| - Traps NVE-decapsulated ARP packets that reached the overlay network. |
| This is required, for example, when the address that needs to be |
| resolved is a local address |
| * - ``ipv6_neigh_solicit`` |
| - ``control`` |
| - Traps IPv6 Neighbour Solicitation packets |
| * - ``ipv6_neigh_advert`` |
| - ``control`` |
| - Traps IPv6 Neighbour Advertisement packets |
| * - ``ipv4_bfd`` |
| - ``control`` |
| - Traps IPv4 BFD packets |
| * - ``ipv6_bfd`` |
| - ``control`` |
| - Traps IPv6 BFD packets |
| * - ``ipv4_ospf`` |
| - ``control`` |
| - Traps IPv4 OSPF packets |
| * - ``ipv6_ospf`` |
| - ``control`` |
| - Traps IPv6 OSPF packets |
| * - ``ipv4_bgp`` |
| - ``control`` |
| - Traps IPv4 BGP packets |
| * - ``ipv6_bgp`` |
| - ``control`` |
| - Traps IPv6 BGP packets |
| * - ``ipv4_vrrp`` |
| - ``control`` |
| - Traps IPv4 VRRP packets |
| * - ``ipv6_vrrp`` |
| - ``control`` |
| - Traps IPv6 VRRP packets |
| * - ``ipv4_pim`` |
| - ``control`` |
| - Traps IPv4 PIM packets |
| * - ``ipv6_pim`` |
| - ``control`` |
| - Traps IPv6 PIM packets |
| * - ``uc_loopback`` |
| - ``control`` |
| - Traps unicast packets that need to be routed through the same layer 3 |
| interface from which they were received. Such packets are routed by the |
| kernel, but also cause it to potentially generate ICMP redirect packets |
| * - ``local_route`` |
| - ``control`` |
| - Traps unicast packets that hit a local route and need to be locally |
| delivered |
| * - ``external_route`` |
| - ``control`` |
| - Traps packets that should be routed through an external interface (e.g., |
| management interface) that does not belong to the same device (e.g., |
| switch ASIC) as the ingress interface |
| * - ``ipv6_uc_dip_link_local_scope`` |
| - ``control`` |
| - Traps unicast IPv6 packets that need to be routed and have a destination |
| IP address with a link-local scope (i.e., fe80::/10). The trap allows |
| device drivers to avoid programming link-local routes, but still receive |
| packets for local delivery |
| * - ``ipv6_dip_all_nodes`` |
| - ``control`` |
| - Traps IPv6 packets that their destination IP address is the "All Nodes |
| Address" (i.e., ff02::1) |
| * - ``ipv6_dip_all_routers`` |
| - ``control`` |
| - Traps IPv6 packets that their destination IP address is the "All Routers |
| Address" (i.e., ff02::2) |
| * - ``ipv6_router_solicit`` |
| - ``control`` |
| - Traps IPv6 Router Solicitation packets |
| * - ``ipv6_router_advert`` |
| - ``control`` |
| - Traps IPv6 Router Advertisement packets |
| * - ``ipv6_redirect`` |
| - ``control`` |
| - Traps IPv6 Redirect Message packets |
| * - ``ipv4_router_alert`` |
| - ``control`` |
| - Traps IPv4 packets that need to be routed and include the Router Alert |
| option. Such packets need to be locally delivered to raw sockets that |
| have the IP_ROUTER_ALERT socket option set |
| * - ``ipv6_router_alert`` |
| - ``control`` |
| - Traps IPv6 packets that need to be routed and include the Router Alert |
| option in their Hop-by-Hop extension header. Such packets need to be |
| locally delivered to raw sockets that have the IPV6_ROUTER_ALERT socket |
| option set |
| * - ``ptp_event`` |
| - ``control`` |
| - Traps PTP time-critical event messages (Sync, Delay_req, Pdelay_Req and |
| Pdelay_Resp) |
| * - ``ptp_general`` |
| - ``control`` |
| - Traps PTP general messages (Announce, Follow_Up, Delay_Resp, |
| Pdelay_Resp_Follow_Up, management and signaling) |
| * - ``flow_action_sample`` |
| - ``control`` |
| - Traps packets sampled during processing of flow action sample (e.g., via |
| tc's sample action) |
| * - ``flow_action_trap`` |
| - ``control`` |
| - Traps packets logged during processing of flow action trap (e.g., via |
| tc's trap action) |
| |
| Driver-specific Packet Traps |
| ============================ |
| |
| Device drivers can register driver-specific packet traps, but these must be |
| clearly documented. Such traps can correspond to device-specific exceptions and |
| help debug packet drops caused by these exceptions. The following list includes |
| links to the description of driver-specific traps registered by various device |
| drivers: |
| |
| * :doc:`netdevsim` |
| * :doc:`mlxsw` |
| |
| .. _Generic-Packet-Trap-Groups: |
| |
| Generic Packet Trap Groups |
| ========================== |
| |
| Generic packet trap groups are used to aggregate logically related packet |
| traps. These groups allow the user to batch operations such as setting the trap |
| action of all member traps. In addition, ``devlink-trap`` can report aggregated |
| per-group packets and bytes statistics, in case per-trap statistics are too |
| narrow. The description of these groups must be added to the following table: |
| |
| .. list-table:: List of Generic Packet Trap Groups |
| :widths: 10 90 |
| |
| * - Name |
| - Description |
| * - ``l2_drops`` |
| - Contains packet traps for packets that were dropped by the device during |
| layer 2 forwarding (i.e., bridge) |
| * - ``l3_drops`` |
| - Contains packet traps for packets that were dropped by the device during |
| layer 3 forwarding |
| * - ``l3_exceptions`` |
| - Contains packet traps for packets that hit an exception (e.g., TTL |
| error) during layer 3 forwarding |
| * - ``buffer_drops`` |
| - Contains packet traps for packets that were dropped by the device due to |
| an enqueue decision |
| * - ``tunnel_drops`` |
| - Contains packet traps for packets that were dropped by the device during |
| tunnel encapsulation / decapsulation |
| * - ``acl_drops`` |
| - Contains packet traps for packets that were dropped by the device during |
| ACL processing |
| * - ``stp`` |
| - Contains packet traps for STP packets |
| * - ``lacp`` |
| - Contains packet traps for LACP packets |
| * - ``lldp`` |
| - Contains packet traps for LLDP packets |
| * - ``mc_snooping`` |
| - Contains packet traps for IGMP and MLD packets required for multicast |
| snooping |
| * - ``dhcp`` |
| - Contains packet traps for DHCP packets |
| * - ``neigh_discovery`` |
| - Contains packet traps for neighbour discovery packets (e.g., ARP, IPv6 |
| ND) |
| * - ``bfd`` |
| - Contains packet traps for BFD packets |
| * - ``ospf`` |
| - Contains packet traps for OSPF packets |
| * - ``bgp`` |
| - Contains packet traps for BGP packets |
| * - ``vrrp`` |
| - Contains packet traps for VRRP packets |
| * - ``pim`` |
| - Contains packet traps for PIM packets |
| * - ``uc_loopback`` |
| - Contains a packet trap for unicast loopback packets (i.e., |
| ``uc_loopback``). This trap is singled-out because in cases such as |
| one-armed router it will be constantly triggered. To limit the impact on |
| the CPU usage, a packet trap policer with a low rate can be bound to the |
| group without affecting other traps |
| * - ``local_delivery`` |
| - Contains packet traps for packets that should be locally delivered after |
| routing, but do not match more specific packet traps (e.g., |
| ``ipv4_bgp``) |
| * - ``external_delivery`` |
| - Contains packet traps for packets that should be routed through an |
| external interface (e.g., management interface) that does not belong to |
| the same device (e.g., switch ASIC) as the ingress interface |
| * - ``ipv6`` |
| - Contains packet traps for various IPv6 control packets (e.g., Router |
| Advertisements) |
| * - ``ptp_event`` |
| - Contains packet traps for PTP time-critical event messages (Sync, |
| Delay_req, Pdelay_Req and Pdelay_Resp) |
| * - ``ptp_general`` |
| - Contains packet traps for PTP general messages (Announce, Follow_Up, |
| Delay_Resp, Pdelay_Resp_Follow_Up, management and signaling) |
| * - ``acl_sample`` |
| - Contains packet traps for packets that were sampled by the device during |
| ACL processing |
| * - ``acl_trap`` |
| - Contains packet traps for packets that were trapped (logged) by the |
| device during ACL processing |
| |
| Packet Trap Policers |
| ==================== |
| |
| As previously explained, the underlying device can trap certain packets to the |
| CPU for processing. In most cases, the underlying device is capable of handling |
| packet rates that are several orders of magnitude higher compared to those that |
| can be handled by the CPU. |
| |
| Therefore, in order to prevent the underlying device from overwhelming the CPU, |
| devices usually include packet trap policers that are able to police the |
| trapped packets to rates that can be handled by the CPU. |
| |
| The ``devlink-trap`` mechanism allows capable device drivers to register their |
| supported packet trap policers with ``devlink``. The device driver can choose |
| to associate these policers with supported packet trap groups (see |
| :ref:`Generic-Packet-Trap-Groups`) during its initialization, thereby exposing |
| its default control plane policy to user space. |
| |
| Device drivers should allow user space to change the parameters of the policers |
| (e.g., rate, burst size) as well as the association between the policers and |
| trap groups by implementing the relevant callbacks. |
| |
| If possible, device drivers should implement a callback that allows user space |
| to retrieve the number of packets that were dropped by the policer because its |
| configured policy was violated. |
| |
| Testing |
| ======= |
| |
| See ``tools/testing/selftests/drivers/net/netdevsim/devlink_trap.sh`` for a |
| test covering the core infrastructure. Test cases should be added for any new |
| functionality. |
| |
| Device drivers should focus their tests on device-specific functionality, such |
| as the triggering of supported packet traps. |
