Cumulus Networks recommends you use a VLAN-aware bridge on your switch. You use traditional mode bridges only if you need to run more than one bridge on the switch or if you need to use PVSTP+.

Contents

 This topic describes ...

Create a Traditional Mode Bridge

You can configure a traditional mode bridge either using NCLU or manually editing the /etc/network/interfaces file.

Configure a Traditional Bridge with NCLU

NCLU has limited support for configuring bridges in traditional mode.  

The traditional bridge must be named something other than bridge, as that name is reserved for the single VLAN-aware bridge that you can configure on the switch. 

The following example shows how to create a simple traditional mode bridge configuration on the switch, including adding the switch ports that are members of the bridge. You can choose to add one or more of the following elements to the configuration:

  • You can add an IP address to provide IP access to the bridge interface. 
  • You can use glob syntax to specify a range of interfaces.
  • You can set two STP attributes on the bridge ports: portautoedge and portrestrole.

    The portautoedge attribute defaults to yes; to use a setting other than the default, you must set this attribute to no

    The portrestrrole attribute defaults to no, but to use a setting other than the default, you must specify this attribute without setting an option. 

    The defaults for these attributes do not appear in the NCLU configuration.

To configure a traditional mode bridge using NCLU, do the following:

cumulus@switch:~$ net add bridge my_bridge_A ports swp1-4
cumulus@switch:~$ net add bridge my_bridge_A ip address 10.10.10.10/24
cumulus@switch:~$ net add interface swp1 stp portautoedge no
cumulus@switch:~$ net add interface swp2 stp portrestrrole
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

These commands create the following configuration snippet in the /etc/network/interfaces file:

cumulus@switch:~$ cat /etc/network/interfaces
 
...

auto swp1
iface swp1
    mstpctl-portautoedge no

auto swp2
iface swp2
    mstpctl-portrestrrole yes

auto swp3
iface swp3

auto swp4
iface swp4

...
auto my_bridge_A 
iface my_bridge_A 
    address 10.10.10.10/24 
    bridge-ports swp1 swp2 swp3 swp4 
    bridge-vlan-aware no

Verify the configuration by running net show config commands:

cumulus@switch:~$ net show config commands
...
net add bridge my_bridge_A ip address 10.10.10.10/24
net add bridge my_bridge_A ports swp1,swp2,swp3,swp4
...
net add interface swp1 stp portautoedge no
net add interface swp2 stp portrestrrole
...

Manually Configure a Traditional Mode Bridge

To create a traditional mode bridge manually, you need to hand edit the /etc/network/interfaces file:

  1. Open the /etc/network/interfaces file in a text editor.
  2. Add a new stanza to create the bridge, and save the file. The example below creates a bridge with STP enabled and the MAC address ageing timer configured to a lower value than the default:

    auto my_bridge
    iface my_bridge
        bridge-ports bond0 swp5 swp6
        bridge-ageing 150
        bridge-stp on
    Configuration OptionDescriptionDefault Value
    bridge-portsList of logical and physical ports belonging to the logical bridge.N/A
    bridge-ageingMaximum amount of time before a MAC addresses learned on the bridge expires from the bridge MAC cache.1800 seconds
    bridge-stp

    Enables spanning tree protocol on this bridge. The default spanning tree mode is Per VLAN Rapid Spanning Tree Protocol (PVRST).

    For more information on spanning-tree configurations see the configuration section: Spanning Tree and Rapid Spanning Tree.

    off

    The name of the bridge must be:

    • Compliant with Linux interface naming conventions.
    • Unique within the switch.
    Do not try to bridge the management port, eth0, with any switch ports (like swp0, swp1, and so forth). For example, if you created a bridge with eth0 and swp1, it will not work.
  3. Reload the network configuration using the ifreload command:

    cumulus@switch:~$ sudo ifreload -a

You can configure multiple bridges, in order to logically divide a switch into multiple layer 2 domains. This allows for hosts to communicate with other hosts in the same domain, while separating them fro hosts in other domains. 

You can create only one VLAN-aware bridge on a switch.

The diagram below shows a multiple bridge configuration, where host-1 and host-2 are connected to bridge-A, while host-3 and host-4 are connected to bridge-B. This means that:

  • host-1 and host-2 can communicate with each other.
  • host-3 and host-4 can communicate with each other.
  • host-1 and host-2 cannot communicate with host-3 and host-4.

This example configuration looks like this in the /etc/network/interfaces file:

auto bridge-A
iface bridge-A
    bridge-ports swp1 swp2
    bridge-stp on

auto bridge-B
iface bridge-B
    bridge-ports swp3 swp4
    bridge-stp on

Trunks in Traditional Bridge Mode

The IEEE standard for trunking is 802.1Q. The 802.1Q specification adds a 4 byte header within the Ethernet frame that identifies the VLAN of which the frame is a member.

802.1Q also identifies an  untagged frame as belonging to the native VLAN (most network devices default their native VLAN to 1). The concept of native, non-native, tagged or untagged has generated confusion due to mixed terminology and vendor-specific implementations. Some clarification is in order:

  • A  trunk port is a switch port configured to send and receive 802.1Q tagged frames.
  • A switch sending an untagged (bare Ethernet) frame on a trunk port is sending from the native VLAN defined on the trunk port.
  • A switch sending a tagged frame on a trunk port is sending to the VLAN identified by the 802.1Q tag.
  • A switch receiving an untagged (bare Ethernet) frame on a trunk port places that frame in the native VLAN defined on the trunk port.
  • A switch receiving a tagged frame on a trunk port places that frame in the VLAN identified by the 802.1Q tag.

A bridge in traditional mode has no concept of trunks, just tagged or untagged frames. With a trunk of 200 VLANs, there would need to be 199 bridges, each containing a tagged physical interface, and one bridge containing the native untagged VLAN. See the examples below for more information.

The interaction of tagged and un-tagged frames on the same trunk often leads to undesired and unexpected behavior. A switch that uses VLAN 1 for the native VLAN may send frames to a switch that uses VLAN 2 for the native VLAN, thus merging those two VLANs and their spanning tree state.

Trunk Example

To create the above example, add the following configuration to the /etc/network/interfaces file:

auto br-VLAN100
iface br-VLAN100
 bridge-ports swp1.100 swp2.100
 bridge-stp on


auto br-VLAN200
iface br-VLAN200
 bridge-ports swp1.200 swp2.200
 bridge-stp on

VLAN Tagging Examples

You can find more examples of VLAN tagging in this chapter.

Configure ARP Timers

Cumulus Linux does not often interact directly with end systems as much as end systems interact with one another. Thus, after a successful address resolution protocol (ARP) places a neighbor into a reachable state, Cumulus Linux may not interact with the client again for a long enough period of time for the neighbor to move into a stale state. To keep neighbors in the reachable state, Cumulus Linux includes a background process (/usr/bin/neighmgrd) that tracks neighbors that move into a stale, delay or probe state, and attempts to refresh their state ahead of any removal from the Linux kernel, and thus before it would be removed from the hardware forwarding.

The ARP refresh timer defaults to 1080 seconds (18 minutes). You can change this setting by following the procedures outlined in this knowledge base article.

Caveats

On Broadcom switches, when two VLAN subinterfaces are bridged to each other in a traditional mode bridge, switchd does not assign an internal resource ID to the subinterface, which is expected for each VLAN subinterface.
To work around this issue, add a VXLAN on the bridge so that it does not require a real tunnel IP address.