The following sections describe various ways you can troubleshoot ifupdown2


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Enabling Logging for Networking

The /etc/default/networking file contains two settings for logging: 

  • To get ifupdown2 logs when the switch boots (stored in syslog)
  • To enable logging when you run systemctl [start|stop|reload] networking.service

This file also contains an option for excluding interfaces when you boot the switch or run systemctl start|stop|reload networking.service . You can exclude any interface specified in /etc/network/interfaces. These interfaces do not come up when you boot the switch or start/stop/reload the networking service. 

cumulus@switch:~$ cat /etc/default/networking
# Parameters for the /etc/init.d/networking script

# Change the below to yes if you want verbose logging to be enabled

# Change the below to yes if you want debug logging to be enabled

# Change the below to yes if you want logging to go to syslog

# Exclude interfaces

Using ifquery to Validate and Debug Interface Configurations

You use  ifquery to print parsed interfaces file entries.

To use ifquery to pretty print iface entries from the interfaces file, run:

cumulus@switch:~$ sudo ifquery bond0
auto bond0
iface bond0
    address 2001:ded:beef:2::1/64
    bond-slaves swp25 swp26

Use ifquery --check to check the current running state of an interface within the interfaces file. It will return exit code 0 or 1 if the configuration does not match. The line bond-xmit-hash-policy layer3+7 below fails because it should read bond-xmit-hash-policy layer3+4.

cumulus@switch:~$ sudo ifquery --check bond0
iface bond0
    bond-xmit-hash-policy layer3+7  [fail]
    bond-slaves swp25 swp26         [pass]
    address             [pass]
    address 2001:ded:beef:2::1/64   [pass]
ifquery --check is an experimental feature.

Use ifquery --running to print the running state of interfaces in the interfaces file format:

cumulus@switch:~$ sudo ifquery --running bond0
auto bond0
iface bond0
    bond-slaves swp25 swp26
    address 2001:ded:beef:2::1/64

ifquery --syntax-help provides help on all possible attributes supported in the interfaces file. For complete syntax on the interfaces file, see man interfaces and man ifupdown-addons-interfaces.

You can use ifquery --print-savedstate to check the ifupdown2 state database. ifdown works only on interfaces present in this state database.

cumulus@leaf1$ sudo ifquery --print-savedstate eth0  
auto eth0
iface eth0 inet dhcp

Debugging Mako Template Errors

An easy way to debug and get details about template errors is to use the mako-render command on your interfaces template file or on /etc/network/interfaces itself. 

cumulus@switch:~$ sudo mako-render /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
auto eth0
iface eth0 inet dhcp
#auto eth1
#iface eth1 inet dhcp
# Include any platform-specific interface configuration
source /etc/network/interfaces.d/*.if
# ssim2 added
auto swp45
iface swp45

auto swp46
iface swp46
cumulus@switch:~$ sudo mako-render /etc/network/interfaces.d/<interfaces_stub_file>

ifdown Cannot Find an Interface that Exists

If you are trying to bring down an interface that you know exists, use ifdown with the --use-current-config option to force ifdown to check the current /etc/network/interfaces file to find the interface. This can solve issues where the ifup command issues for that interface was interrupted before it updated the state database. For example:

cumulus@switch:~$ sudo ifdown br0
error: cannot find interfaces: br0 (interface was probably never up ?)

cumulus@switch:~$ sudo brctl show
bridge name	bridge id		STP enabled	interfaces
br0		8000.44383900279f	yes		downlink

cumulus@switch:~$ sudo ifdown br0 --use-current-config 

Removing All References to a Child Interface

If you have a configuration with a child interface, whether it's a VLAN, bond or another physical interface, and you remove that interface from a running configuration, you must remove every reference to it in the configuration. Otherwise, the interface continues to be used by the parent interface.

For example, consider the following configuration:

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp

auto bond1
iface bond1
    bond-slaves swp2 swp1

auto bond3
iface bond3
    bond-slaves swp8 swp6 swp7

auto br0
iface br0
    bridge-ports swp3 swp5 bond1 swp4 bond3
    bridge-pathcosts  swp3=4 swp5=4 swp4=4
    address 2001::10/64

Notice that bond1 is a member of br0. If bond1 is removed, you must remove the reference to it from the br0 configuration. Otherwise, if you reload the configuration with ifreload -a, bond1 is still part of br0.

MTU Set on a Logical Interface Fails with Error: "Numerical result out of range"

This error occurs when the MTU you are trying to set on an interface is higher than the MTU of the lower interface or dependent interface. Linux expects the upper interface to have an MTU less than or equal to the MTU on the lower interface. 

In the example below, the swp1.100 VLAN interface is an upper interface to physical interface swp1. If you want to change the MTU to 9000 on the VLAN interface, you must include the new MTU on the lower interface swp1 as well.

auto swp1.100 
iface swp1.100 
    mtu 9000 

auto swp1 
iface swp1  
    mtu 9000

Interpreting iproute2 batch Command Failures

ifupdown2 batches iproute2 commands for performance reasons. A batch command contains ip -force -batch - in the error message. The command number that failed is at the end of this line: Command failed -:1.

Below is a sample error for the command 1: link set dev host2 master bridge. There was an error adding the bond host2 to the bridge named bridge because host2 did not have a valid address.

error: failed to execute cmd 'ip -force -batch - [link set dev host2 master bridge
addr flush dev host2
link set dev host1 master bridge
addr flush dev host1
]'(RTNETLINK answers: Invalid argument 
Command failed -:1) 
warning: bridge configuration failed (missing ports) 

Understanding the "RTNETLINK answers: Invalid argument" Error when Adding a Port to a Bridge

This error can occur when the bridge port does not have a valid hardware address.

This can typically occur when the interface being added to the bridge is an incomplete bond; a bond without slaves is incomplete and does not have a valid hardware address.

MLAG Peerlink Interface Drops Many Packets

Losing a large number of packets across an MLAG peerlink interface may not be a problem. Instead this could be occurring in order to prevent looping of BUM (broadcast, unknown unicast and multicast) packets. For more information, and how to detect these drops, read the MLAG chapter.