Tools for Resolving Compute Node Boot Issues

A number of tools can be used to analyze and debug issues encountered during the compute node boot process. The underlying issue and symptoms dictate the type of tool required.

nmap

Use nmap to send out DHCP discover requests to test DHCP. nmap can be installed using the following command:

zypper install nmap

To reach the DHCP server, the request generally needs to be sent over the Node Management network (NMN) from a non-compute node (NCN).

In the following example, nmap is used to send a broadcast request over the eth1 interface:

nmap --script broadcast-dhcp-discover -e eth1

Wireshark

Use Wireshark to display network traffic. It has powerful display filters that help find information that can be used for debugging. To learn more, visit the Wireshark home page.

tcpdump

Use tcpdump to capture network traffic, such as DHCP or TFTP requests. It can be installed using the following mechanisms:

  • Install tcpdump inside an Alpine-based pod:

    apk add --no-cache tcpdump

  • Install tcpdump on an NCN or some other node that is running SUSE:

    zypper install tcpdump

Invoking tcpdump without any arguments will write all of its output to stdout. This is reasonable for some tasks, but the volume of traffic that tcpdump can capture is large, so it is often better to write the output to a file.

Use the following command to send tcpdump output to stdout:

tcpdump

Use the following command to send tcpdump output to a file (/tmp/tcpdump.output in the following example):

tcpdump -w /tmp/tcpdump.output

Use either tcpdump or Wireshark to read from the tcpdump file. Here is how to read the file using tcpdump:

tcpdump -r /tmp/tcpdump.output

Filtering the traffic using tcpdump filters is not recommended because when a TFTP server answers a client, it will usually use an ephemeral port that the user may not be able to identify and will not be captured by tcpdump. It is better to capture everything with tcpdump and then filter with Wireshark when looking at the resulting output. Filtering on DHCP traffic can be performed because that uses ports 67 and 68 specifically.

TFTP client

Use a TFTP client to send TFTP requests to the TFTP server. This will test that the server is functional. TFTP requests can be sent from the NCN, remote node, or laptop, as long as it targets the NMN.

Install the TFTP client using the following command:

zypper install atftp

The atftp TFTP client can be used to request files from the TFTP server. The TFTP server is on the NMN and listens on port 69. The TFTP server sends the ipxe.efi file as the response in this example.

Request the files:

atftp
tftp> connect 10.100.160.2 69
tftp> get ipxe.efi test-ipxe.efi
tftp> quit

List the files:

ls -l test-ipxe.efi

Example output:

-rw-r--r-- 1 root root 951904 Sep 11 10:44 test-ipxe.efi

Serial Over LAN (SOL) sessions

There are two tools that can be used to access a BMC’s console via SOL:

  • ipmitool

    ipmitool is a utility for controlling IPMI-enabled devices.

    Use the following command to access a node’s SOL via ipmitool:

    read -s is used to prevent the password from being written to the screen or the shell history.

    USERNAME=root
read -r -s -p "BMC ${USERNAME} password: " IPMI_PASSWORD

    export IPMI_PASSWORD
ipmitool -I lanplus -U "${USERNAME}" -E -H <node_management_network_IP_address_of_node> sol activate

    Example:

    ipmitool -I lanplus -U "${USERNAME}" -E -H  10.100.165.2 sol activate

  • ConMan

    The ConMan tool is used to collect logs from nodes. It is also used to attach to the node’s SOL console. For more information, refer to ConMan and Access Compute Node Logs.