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 can monitor layer 1, layer 2, layer 3, tunnel, buffer and ACL related issues. Cumulus Linux enables and runs the WJH service by default.
Configure WJH
You can choose which packet drops you want to monitor by creating channels and setting the packet drop categories (layer 1, layer 2, layer 3, tunnel, buffer and ACL ) you want to monitor.
NVUE does not provide commands to set the buffer and ACL packet drop categories. You must edit the /etc/what-just-happened/what-just-happened.json file. See the Linux Commands tab.
The following example configures two separate channels:
- The
forwardingchannel monitors layer 2, layer 3, and tunnel packet drops. - The
layer-1channel monitors layer 1 packet drops.
cumulus@switch:~$ nv set system wjh channel forwarding trigger l2
cumulus@switch:~$ nv set system wjh channel forwarding trigger l3
cumulus@switch:~$ nv set system wjh channel forwarding trigger tunnel
cumulus@switch:~$ nv set system wjh channel layer-1 trigger l1
cumulus@switch:~$ nv config apply
You can stop monitoring specific packet drops by unsetting a category in the channel list. The following command example stops monitoring layer 2 packet drops that are in the forwarding channel:
cumulus@switch:~$ nv unset system wjh channel forwarding trigger l2
cumulus@switch:~$ nv config apply
To remove a channel, run the nv unset system wjh channel <channel> command. The following command example removes the layer-1 channel:
cumulus@switch:~$ nv unset system wjh channel layer-1
cumulus@switch:~$ nv config apply
Edit the /etc/what-just-happened/what-just-happened.json file:
- For each drop category you want to monitor, include the drop category value inside the square brackets ([]).
- For each drop category you do not want to monitor, remove the drop category value from inside the square brackets.
After you edit the file, you must restart the WJH service with the sudo systemctl restart what-just-happened command.
The following example configures a channel to monitor layer 2, layer 3, and tunnel packet drops and a channel to monitor layer 1 packet drops.
cumulus@switch:~$ sudo nano /etc/what-just-happened/what-just-happened.json
{
"what-just-happened": {
"channels": {
"forwarding": {
"drop_category_list": [
"l2",
"l3",
"tunnel"
]
},
"layer-1": {
"drop_category_list": [
"l1"
]
}
}
}
}
cumulus@switch:~$ sudo systemctl restart what-just-happened
The following example configures a channel to monitor buffer packet drops and a channel to monitor ACL packet drops.
cumulus@switch:~$ sudo nano /etc/what-just-happened/what-just-happened.json
{
"what-just-happened": {
"channels": {
"buffer": {
"drop_category_list": ["buffer"]
},
"acl": {
"drop_category_list": ["acl"]
}
}
}
}
cumulus@switch:~$ sudo systemctl restart what-just-happened
Show Information about Dropped Packets
You can run the following commands to show information about dropped packets and diagnose problems.
To show information about packet drops for all the channels you configure, run the nv show system wjh packet-buffer command. The command output includes the reason for the drop and the recommended action to take.
You can also show the WJH configuration on the switch:
- To show the configuration for a channel, run the
nv show system wjh channel <channel>command. For example,nv show system wjh channel forwarding. - To show the configuration for packet drop categories in a channel, run the
nv show system wjh channel <channel> triggercommand. For example,nv show system wjh channel forwarding trigger.
The following example shows information about layer 1 packet drops:
cumulus@switch:~$ nv show system wjh packet-buffer
# dMAC dPort Dst IP:Port EthType Drop group IP Proto Drop reason - Recommended action Severity sMAC sPort Src IP:Port Timestamp VLAN
-- ---- ----- ----------- ------- ---------- -------- ------------------------------------------------------- -------- ---- ------- ----------- --------------------- ----
1 N/A N/A N/A N/A L1 N/A Generic L1 event - Check layer 1 aggregated information Warn N/A swp17 N/A 22/11/03 01:00:35.458 N/A
2 N/A N/A N/A N/A L1 N/A Generic L1 event - Check layer 1 aggregated information Warn N/A swp18 N/A 22/11/03 01:00:35.458 N/A
3 N/A N/A N/A N/A L1 N/A Generic L1 event - Check layer 1 aggregated information Warn N/A swp19 N/A 22/11/03 01:00:35.458 N/A
4 N/A N/A N/A N/A L1 N/A Generic L1 event - Check layer 1 aggregated information Warn N/A swp20 N/A 22/11/03 01:00:35.458 N/A
You can run the following commands from the command line.
Command |
Description |
|---|---|
what-just-happened poll |
Shows information about packet drops for all the channels you configure. The output includes the reason for the drop and the recommended action to take. The what-just-happened poll <channel> command shows information for the channel you specify. |
what-just-happened poll --aggregate |
Shows information about dropped packets aggregated by the reason for the drop. This command also shows the number of times the dropped packet occurs. The what-just-happened poll <channel> --aggregate command shows information for the channel you specify. |
what-just-happened poll --export |
Saves information about dropped packets to a file in PCAP format. The what-just-happened poll <channel> --export command saves information for the channel you specify. |
what-just-happened poll --export --no_metadata |
Saves information about dropped packets to a file in PCAP format without metadata. The what-just-happened poll <channel> --export --no_metadata command saves information for the channel you specify. |
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.
To show all dropped packets and the reason for the drop, run the NVUE nv show system wjh packet-buffer command or the what-just-happened poll command.
The following example shows that packets drop five times because the source MAC address equals the destination MAC address:
cumulus@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
cumulus@switch:~$ what-just-happened poll --export --no_metadata
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
Buffer Packet Drop Monitoring
- Buffer packet drop monitoring is available on a switch with Spectrum-2 and later.
- Buffer packet drop monitoring uses a SPAN destination. If you configure SPAN, ensure that you do not exceed the total number of SPAN destinations allowed for your switch ASIC type; see SPAN and ERSPAN. If you need to remove the SPAN destination that buffer packet drop monitoring uses, delete the buffer monitoring drop category from the
/etc/what-just-happened/what-just-happened.jsonfile and reload thewhat-just-happenedservice.
Cumulus Linux and Docker
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".
WJH and the NVIDIA NetQ Agent
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:~$ nv set system wjh enable on
cumulus@switch:~$ nv config apply
cumulus@switch:~$ sudo systemctl enable what-just-happened
cumulus@switch:~$ sudo systemctl start what-just-happened