What Just Happened (WJH)
What Just Happened (WJH) provides real time visibility into network problems and has two components:
-
The WJH agent enables you to stream detailed and contextual telemetry for off-switch analysis with tools, such as NVIDIA NetQ.
-
The WJH service (
what-just-happened) enables you to diagnose network problems by looking at dropped packets. WJH monitors forwarding (layer 2, layer 3, and tunnel) related issues. Cumulus Linux enables the WJH service by default.When you enable the NVIDIA NetQ agent on the switch, the WJH service stops and does not run. If you disable the NVIDIA NetQ service and want to use WJH, run the following commands to enable and start the WJH service:
cumulus@switch:~$ sudo systemctl enable what-just-happened cumulus@switch:~$ sudo systemctl start what-just-happened
Run WJH Commands
You can run the following commands from the command line.
Command |
Description |
|---|---|
what-just-happened poll |
Shows information about dropped packets due to forwarding-related issues (layer 2, layer 3, and tunnel only). The output includes the reason for the drop and the recommended action to take. The what-just-happened poll forwarding command shows the same information. |
what-just-happened poll --aggregate |
Shows information about dropped packets due to forwarding-related issues aggregated by the reason for the drop. This command also shows the number of times the dropped packet occurs. The what-just-happened poll forwarding --aggregate command shows the same information. |
what-just-happened poll --export |
Saves information about dropped packets due to forwarding-related issues into a file in PCAP format. The what-just-happened poll forwarding --export command shows the same information. |
what-just-happened poll --export --no_metadata |
Saves information about dropped packets due to forwarding-related issues into a file in PCAP format without metadata. The what-just-happened poll forwarding --export --no_metadata command shows the same information. |
what-just-happened dump |
Displays all diagnostic information on the command line. |
Run the what-just-happened -h command to see all the WJH command options. (WJH only supports the forwarding channel.)
Command Examples
The following example shows all dropped packets and the reason for the drop:
root@switch:~# what-just-happened poll
# Timestamp sPort dPort VLAN sMAC dMAC EthType Src IP:Port Dst IP:Port IP Proto Drop Severity Drop reason - Recommended action
Group
---- ---------------------- ------ ------ ----- ------------------ ------------------ -------- ------------ ------------ --------- ------ --------- -----------------------------------------------
1 21/06/16 12:02:42.052 swp1 N/A N/A 44:38:39:00:a4:84 44:38:39:00:a4:84 IPv4 N/A N/A N/A L2 Error Source MAC equals destination MAC - Bad packet was received from peer
2 21/06/16 12:02:42.052 swp1 N/A N/A 44:38:39:00:a4:84 44:38:39:00:a4:84 IPv4 N/A N/A N/A L2 Error Source MAC equals destination MAC - Bad packet was received from peer
3 21/06/16 12:02:42.052 swp1 N/A N/A 44:38:39:00:a4:84 44:38:39:00:a4:84 IPv4 N/A N/A N/A L2 Error Source MAC equals destination MAC - Bad packet was received from peer
4 21/06/16 12:02:42.069 swp1 N/A N/A 44:38:39:00:a4:84 44:38:39:00:a4:84 IPv4 N/A N/A N/A L2 Error Source MAC equals destination MAC - Bad packet was received from peer
The following example shows that packets drop five times because the source MAC address equals the destination MAC address:
root@switch:~# what-just-happened poll --aggregate
Sample Window : 2021/06/16 12:57:23.046 - 2021/06/16 14:46:17.701
# sPort VLAN sMAC dMAC EthType Src IP:Port Dst IP:Port IP Proto Count Severity Drop reason - Recommended action
-- ------ ----- ------------------ ------------------ -------- ------------ ------------ --------- ------ --------- -----------------------------------------------
1 swp4 N/A 44:38:39:00:a4:87 44:38:39:00:a4:87 IPv4 0.0.0.0:0 0.0.0.0:0 ip 100 Error Source MAC equals destination MAC - Bad packet was received from peer
2 swp1 N/A 44:38:39:00:a4:80 44:38:39:00:a4:80 IPv4 0.0.0.0:0 0.0.0.0:0 ip 100 Error Source MAC equals destination MAC - Bad packet was received from peer
The following command saves dropped packets to a file in PCAP format
root@switch:~# what-just-happened poll --export
PCAP file path : /var/log/mellanox/wjh/wjh_user_2021_06_16_12_03_15.pcap
# Timestamp sPort dPort VLAN sMAC dMAC EthType Src IP:Port Dst IP:Port IP Proto Drop Severity Drop reason - Recommended action
Group
---- ---------------------- ------ ------ ----- ------------------ ------------------ -------- ------------ ------------ --------- ------ --------- -----------------------------------------------
1 21/06/16 12:03:12.728 swp1 N/A N/A 44:38:39:00:a4:84 44:38:39:00:a4:84 IPv4 N/A N/A N/A L2 Error Source MAC equals destination MAC - Bad packet as received from peer
2 21/06/16 12:03:12.728 swp1 N/A N/A 44:38:39:00:a4:84 44:38:39:00:a4:84 IPv4 N/A N/A N/A L2 Error Source MAC equals destination MAC - Bad packet was received from peer
3 21/06/16 12:03:12.745 swp1 N/A N/A 44:38:39:00:a4:84 44:38:39:00:a4:84 IPv4 N/A N/A N/A L2 Error Source MAC equals destination MAC - Bad packet was received from peer
4 21/06/16 12:03:12.745 swp1 N/A N/A 44:38:39:00:a4:84 44:38:39:00:a4:84 IPv4 N/A N/A N/A L2 Error Source MAC equals destination MAC - Bad packet was received from peer
Considerations
WJH runs in a Docker container. By default, when Docker starts, it creates a bridge called docker0. However, for compatibility reasons Cumulus Linux disables the docker0 bridge in the /etc/docker/daemon.json file with the attribute "bridge: none".