Table of Contents
Summary
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Bonding is a technology that allows aggregation of multiple ethernet-like interfaces into a single virtual link, thus getting higher data rates and providing failover.
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Interface bonding does not create an interface with a larger link speed. Interface bonding creates a virtual interface that can load balance traffic over multiple interfaces. More details can be found in the LAG interfaces and load balancing page. |
| Info |
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CRS3xx, CRS5xx series switches, CCR2116, CCR2216 routers and 88E6393X, 88E6191X, 88E6190 switch chips support bridge hardware offloading with bonding interfaces. Only |
Quick Setup Guide
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Let us assume that we have two Ethernet interfaces on each router (Router1 and Router2) and want to get the maximum data rate between these two routers. To make this possible, follow these steps:
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ARP monitoring sends ARP queries and uses the response as an indication that the link is operational. The ARP replies are not validated, so any received packet by the slave interface will result in the slave interface considered as active. This gives assurance that traffic is actually flowing over the links. If balance-rr and balance-xor modes are set, then the switch should be configured to evenly distribute packets across all links. Otherwise, all replies from the ARP targets will be received on the same link which could cause other links to fail. ARP monitoring is enabled by setting three properties - link-monitoring, arp-ip-targets and arp-interval. The meaning of each option is described later in this article. It is possible to specify multiple ARP targets that can be useful in High Availability setups. If only one target is set, the target itself may go down. Having additional targets increases the reliability of the ARP monitoring.
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No additional configuration is required for the switch. The image above illustrates how balance-tlb mode works. As you can see router can communicate to all the clients connected to the switch with a total bandwidth of both links (15Mbps). But as you already know, balance-tlb is not balancing incoming traffic. In our example, clients can communicate to the router with a total bandwidth of primary link which is 10Mbps in our configuration.
balance-alb
The mode is basically the same as balance-tlb but incoming IPv4 traffic is also balancedis basically the same as balance-tlb but incoming IPv4 traffic is also balanced. The receive load balancing is achieved by ARP negotiation. The bonding driver intercepts locally generated ARP messages on their way out and overwrites the source hardware address with the unique address of one of the slaves in the bond such that different peers use different hardware addresses. Only MII link monitoring is supported (ARP link monitoring is ignored when configured), the additional downside downside of this mode is that it requires device driver capability to change MAC address. The mode is not compatible with local-proxy-arp setting.
The image above illustrates how balance-alb mode works. Compared to balance-tlb mode, traffic from clients can also use the secondary link to communicate with the router.
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| Property | Description |
|---|---|
| port (interface) | Used bonding port |
| key (integer) | Shows the local LACP aggregation key, a unique key is generated and used by all bonding ports that are configured on the same LACP group |
| port | |
| key (integer) | Shows the local LACP aggregation key. The lower 6 bits are automatically assigned based on individual port link speed and duplex. The upper 10 bits can be manually specified using the lacp-user-key setting (available only since RouterOS v7.3). |
| flags (string) | Shows the local LACP flags: A - activity (link is active, otherwise passive) |
| partner-sys-id (MAC address) | Shows the partner LACP system ID |
| partner-sys-priority (integer) | Shows the partner LACP priority |
| partner-key (integer)key (integer) | Shows the partner LACP aggregation keyShows the partner LACP aggregation key, a unique key is generated and used by all bonding ports that are configured on the same LACP group |
| partner-flags (string) | Shows the partner LACP flags |
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| Property | Description |
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| arp (disabled | enabled | proxy-arp | reply-only; Default: enabled) | Address Resolution Protocol for the interface.
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| arp-interval (time; Default: 00:00:00.100) | Time in milliseconds defines how often to monitor ARP requests |
| arp-ip-targets (IP address; Default: ) | IP target address which will be monitored if link-monitoring is set to arp. You can specify multiple IP addresses, separated by a comma |
| comment (string; Default: ) | Short description of the interface |
| disabled (yes | no; Default: no) | Changes whether the bonding interface is disabled |
| down-delay (time; Default: 00:00:00) | If a link failure has been detected, the bonding interface is disabled for a down-delay time. The value should be a multiple of mii-interval, otherwise, it will be rounded down to the nearest value. This property only has an effect when link-monitoring is set to mii. |
| forced-mac-address (MAC address; Default: none) | By default, the bonding interface will use the MAC address of the first selected slave interface. This property allows to configure static MAC address for the bond interface (all zeros, broadcast or multicast addresses will not apply). RouterOS will automatically change the MAC address for slave interfaces and it will be visible in /interface ethernet configuration export |
| lacp-rate (1sec | 30secs; Default: 30secs) | Link Aggregation Control Protocol rate specifies how often to exchange with LACPDUs between bonding peers. Used to determine whether a link is up or other changes have occurred in the network. LACP tries to adapt to these changes providing failover. |
| lacp-user-key (integer: 0..1023; Default: 0) | Specifies the upper 10 bits of the port key. The lower 6 bits are automatically assigned based on individual port link speed and duplex. The setting is available only since RouterOS v7.3. |
| link-monitoring (arp | mii | none; Default: mii) | Method to use for monitoring the link (whether it is up or down)
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| min-links (integer: 0..4294967295; Default: 0) | How many active slave links needed for bonding to become active |
| mii-interval (time; Default: 00:00:00.100) | How often to monitor the link for failures (the parameter used only if link-monitoring is mii) |
| mlag-id (integer: 0..4294967295; Default:) | Changes MLAG ID for bonding interface. The same MLAG ID should be used on both peer devices to successfully create a single MLAG. See more details on MLAG. |
| mode (802.3ad | active-backup | balance-alb | balance-rr | balance-tlb | balance-xor | broadcast; Default: balance-rr) | Specifies one of the bonding policies
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| mtu (integer; Default: 1500) | Maximum Transmit Unit in bytes. Must be smaller or equal to the smallest L2MTU value of a bonding slave. L2MTU of a bonding interface is determined by the lowest L2MTU value among its slave interfaces |
| name (string; Default: ) | Name of the bonding interface |
| primary (string; Default: none) | Controls the primary interface between active slave ports, works only for active-backup, balance-tlb and balance-alb modes. For active-backup mode, it controls which running interface is supposed to send and receive the traffic. For balance-tlb mode, it controls which running interface is supposed to receive all the traffic, but for balance-alb mode, it controls which interface is supposed to receive the unbalanced traffic (the non-IPv4 traffic). When none of the interfaces are selected as primary, device will automatically select the interface that is configured as the first one. |
| slaves (string; Default: none) | At least two ethernet-like interfaces separated by a comma, which will be used for bonding |
| up-delay (time; Default: 00:00:00) | If a link has been brought up, the bonding interface is disabled for up-delay time and after this time it is enabled. The value should be a multiple of mii-interval, otherwise, it will be rounded down to the nearest value. This property only has an effect when link-monitoring is set to mii. |
| transmit-hash-policy (layer-2 | layer-2-and-3 | layer-3-and-4; Default: layer-2) | Selects the transmit hash policy to use for slave selection in balance-xor and 802.3ad modes
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