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Cumulus Linux

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If you are using the current version of Cumulus Linux, the content on this page may not be up to date. The current version of the documentation is available here. If you are redirected to the main page of the user guide, then this page may have been renamed; please search for it there.

Bonding - Link Aggregation

Linux bonding provides a method for aggregating multiple network interfaces (slaves) into a single logical bonded interface (bond). Link aggregation is useful for linear scaling of bandwidth, load balancing, and failover protection.

Cumulus Linux supports two bonding modes:

  • IEEE 802.3ad link aggregation mode that allows one or more links to be aggregated together to form a link aggregation group (LAG) so that a media access control (MAC) client can treat the group as if it were a single link. IEEE 802.3ad link aggregation is the default mode.
  • Balance-xor mode, where the bonding of slave interfaces are static and all slave interfaces are active for load balancing and fault tolerance purposes. This is useful for MLAG deployments.

Cumulus Linux uses version 1 of the LAG control protocol (LACP).

To temporarily bring up a bond even when there is no LACP partner, use LACP Bypass.

Hash Distribution

Egress traffic through a bond is distributed to a slave based on a packet hash calculation, providing load balancing over the slaves; many conversation flows are distributed over all available slaves to load balance the total traffic. Traffic for a single conversation flow always hashes to the same slave.

The hash calculation uses packet header data to choose to which slave to transmit the packet:

  • For IP traffic, IP header source and destination fields are used in the calculation.
  • For IP + TCP/UDP traffic, source and destination ports are included in the hash calculation.

In a failover event, the hash calculation is adjusted to steer traffic over available slaves.

LAG Custom Hashing

On Mellanox switches, you can configure which fields are used in the LAG hash calculation. For example, if you do not want to use source or destination port numbers in the hash calculation, you can disable the source port and destination port fields.

You can configure the following fields:

  • Source MAC
  • Destination
  • Source IP
  • Destination IP
  • Ether type
  • VLAN ID
  • Source port
  • Destination port
  • Layer 3 protocol

To configure custom hash, edit the /usr/lib/python2.7/dist-packages/cumulus/__chip_config/mlx/datapath.conf file:

  1. To enable custom hashing, uncomment the lag_hash_config.enable = true line.
  2. To enable a field, set the field to true. To disable a field, set the field to false.
  3. Restart the switchd service:
cumulus@switch:~$ sudo systemctl restart switchd.service

The following shows an example datapath.conf file:

cumulus@switch:~$ sudo nano /usr/lib/python2.7/dist-packages/cumulus/__chip_config/mlx/datapath.conf
...
#LAG HASH config
#HASH config for LACP to enable custom fields
#Fields will be applicable for LAG hash
#calculation
#Uncomment to enable custom fields configured below
lag_hash_config.enable = true

lag_hash_config.smac = true
lag_hash_config.dmac = true
lag_hash_config.sip  = true
lag_hash_config.dip  = true
lag_hash_config.ether_type = true
lag_hash_config.vlan_id = true
lag_hash_config.sport = false
lag_hash_config.dport = false
lag_hash_config.ip_prot = true
...

Symmetric hashing is enabled by default on Mellanox switches. Make sure that the settings for the source IP (lag_hash_config.sip) and destination IP (lag_hash_config.dip) fields match, and that the settings for the source port (lag_hash_config.sport) and destination port (lag_hash_config.dport) fields match; otherwise symmetric hashing is disabled automatically. You can disable symmetric hashing manually in the /etc/cumulus/datapath/traffic.conf file by setting symmetric_hash_enable = FALSE.

You can set a unique hash seed for each switch to help avoid hash polarization. See Configure a Hash Seed to Avoid Hash Polarization.

Create a Bond

In the example below, the front panel port interfaces swp1 thru swp4 are slaves in bond0, while swp5 and swp6 are not part of bond0.

To create and configure a bond:

Run the net add bond command. The example command below creates a bond called bond0 with slaves swp1, swp2, swp3, and swp4:

cumulus@switch:~$ net add bond bond0 bond slaves swp1-4
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

Edit the /etc/network/interfaces file and add a stanza for the bond. The example below creates a bond called bond0 with slaves swp1, swp2, swp3, and swp4:

cumulus@switch:~$ sudo nanno /etc/network/interfaces
...
auto bond0
iface bond0
    bond-slaves swp1 swp2 swp3 swp4
...

Run the ifreload -a command to load the new configuration:

cumulus@switch:~$ ifreload -a

  • The bond is configured by default in IEEE 802.3ad link aggregation mode. To configure the bond in balance-xor mode, see Configuration Parameters below.
  • If the bond is not going to become part of a bridge, you need to specify an IP address.
  • The name of the bond must be compliant with Linux interface naming conventions and unique within the switch.
  • Do not use a dash (-) in the bond name.
  • Cumulus Linux does not support bond members at 200G or greater.

When networking is started on the switch, bond0 is created as MASTER and interfaces swp1 thru swp4 come up in SLAVE mode, as seen in the ip link show command:

cumulus@switch:~$ ip link show
...

3: swp1: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT qlen 500
    link/ether 44:38:39:00:03:c1 brd ff:ff:ff:ff:ff:ff
4: swp2: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT qlen 500
    link/ether 44:38:39:00:03:c1 brd ff:ff:ff:ff:ff:ff
5: swp3: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT qlen 500
    link/ether 44:38:39:00:03:c1 brd ff:ff:ff:ff:ff:ff
6: swp4: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT qlen 500
    link/ether 44:38:39:00:03:c1 brd ff:ff:ff:ff:ff:ff
...

55: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT
    link/ether 44:38:39:00:03:c1 brd ff:ff:ff:ff:ff:ff

All slave interfaces within a bond have the same MAC address as the bond. Typically, the first slave added to the bond donates its MAC address as the bond MAC address, whereas the MAC addresses of the other slaves are set to the bond MAC address. The bond MAC address is used as the source MAC address for all traffic leaving the bond and provides a single destination MAC address to address traffic to the bond.

Configure Bond Options

The configuration options for a bond are are described in the table below. To configure a bond:

Run net add bond <bond-name> bond <option>. The following example sets the bond mode for bond01 to balance-xor:

cumulus@switch:~$ net add bond bond1 bond mode balance-xor
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

Edit the /etc/network/interfaces file and add the parameter to the bond stanza, then load the new configuration. The following example sets the bond mode for bond01 to balance-xor:

cumulus@switch:~$ sudo nanno /etc/network/interfaces
...
auto bond1
iface bond1
    bond-mode balance-xor
    bond-slaves swp1 swp2 swp3 swp4
...

Run the ifreload -a command to load the new configuration:

cumulus@switch:~$ ifreload -a

Each bond configuration option, except for bond slaves, is set to the recommended value by default in Cumulus Linux. Only configure an option if a different setting is needed. For more information on configuration values, refer to the Related Information section below.

Parameter Description
bond-mode 802.3ad|balance-xor Cumulus Linux supports IEEE 802.3ad link aggregation mode (802.3ad) and balance-xor mode.
The default mode is 802.3ad.

Note: When you enable balance-xor mode, the bonding of slave interfaces are static and all slave interfaces are active for load balancing and fault tolerance purposes. Packet transmission on the bond is based on the hash policy specified by xmit-hash-policy.

When using balance-xor mode to dual-connect host-facing bonds in an MLAG environment, you must configure the clag-id parameter on the MLAG bonds and it must be the same on both MLAG switches. Otherwise, the bonds are treated by the MLAG switch pair as single-connected.

Use balance-xor mode only if you cannot use LACP; LACP can detect mismatched link attributes between bond members and can even detect misconnections.
bond-slaves <interface-list> The list of slaves in the bond.
bond miimon <value> Defines how often the link state of each slave is inspected for failures. You can specify a value between 0 and 255. The default value is 100.
bond-use-carrier no Determines the link state.
bond-lacp-bypass-allow Enables LACP bypass.
bond-lacp-rate slow Sets the rate to ask the link partner to transmit LACP control packets. slow is the only option.
bond-min-links Defines the minimum number of links (between 0 and 255) that must be active before the bond is put into service. The default value is 1.

A value greater than 1 is useful if higher level services need to ensure a minimum aggregate bandwidth level before activating a bond. Keeping bond-min-links set to 1 indicates the bond must have at least one active member. If the number of active members drops below the bond-min-links setting, the bond appears to upper-level protocols as link-down. When the number of active links returns to greater than or equal to bond-min-links, the bond becomes link-up.

Show Bond Information

To show information for a bond:

Run the net show interface <bond> command:

cumulus@switch:~$ net show interface bond1
    Name    MAC                Speed    MTU    Mode
--  ------  -----------------  -------  -----  ------
UP  bond1   00:02:00:00:00:12  20G      1500   Bond


Bond Details
---------------  -------------
Bond Mode:       Balance-XOR
Load Balancing:  Layer3+4
Minimum Links:   1
In CLAG:         CLAG Inactive


    Port     Speed      TX    RX    Err    Link Failures
--  -------  -------  ----  ----  -----  ---------------
UP  swp3(P)  10G         0     0      0                0
UP  swp4(P)  10G         0     0      0                0


LLDP
-------  ----  ------------
swp3(P)  ====  swp1(p1c1h1)
swp4(P)  ====  swp2(p1c1h1)Routing
-------
  Interface bond1 is up, line protocol is up
  Link ups:       3    last: 2017/04/26 21:00:38.26
  Link downs:     2    last: 2017/04/26 20:59:56.78
  PTM status: disabled
  vrf: Default-IP-Routing-Table
  index 31 metric 0 mtu 1500
  flags: <UP,BROADCAST,RUNNING,MULTICAST>
  Type: Ethernet
  HWaddr: 00:02:00:00:00:12
  inet6 fe80::202:ff:fe00:12/64
  Interface Type Other

Run the sudo cat /proc/net/bonding/<bond> command:

cumulus@switch:~$ sudo cat /proc/net/bonding/bond01

Ethernet Channel Bonding Driver: v3.7.1 (April 27, 2011)
Bonding Mode: load balancing (xor)
Transmit Hash Policy: layer3+4 (1)
MII Status: up
MII Polling Interval (ms): 100
Up Delay (ms): 0
Down Delay (ms): 0


Slave Interface: swp1
MII Status: up
Speed: 1000 Mbps
Duplex: full
Link Failure Count: 0
Permanent HW addr: 44:38:39:00:00:03
Slave queue ID: 0

The detailed output in /proc/net/bonding/<filename> includes the actor/partner LACP information. This information is not necessary and requires you to use sudo to view the file.

Caveats and Errata

  • An interface cannot belong to multiple bonds.
  • A bond can have subinterfaces, but subinterfaces cannot have a bond.
  • A bond cannot enslave VLAN subinterfaces.
  • Set all slave ports within a bond to the same speed/duplex and make sure they match the link partner’s slave ports.
  • On a Cumulus RMP switch, if you create a bond with multiple 10G member ports, traffic gets dropped when the bond uses members of the same unit listed in the /var/lib/cumulus/porttab file. For example, traffic gets dropped if both swp49 and swp52 are in the bond because they both are in xe0 (or if both swp50 and swp51 are in the same bond because they are both in xe1):
swp49 xe0 0 0 -1 0
swp50 xe1 0 0 -1 0
swp51 xe1 1 0 -1 0
swp52 xe0 1 0 -1 0

Single port member bonds, bonds with different units (xe0 or xe1, as above), or layer 3 bonds do not have this issue.

On Cumulus RMP switches, which are built with two Hurricane2 ASICs, you cannot form an LACP bond on links that terminate on different Hurricane2 ASICs.

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