Legs¶
A leg is an individual Internet connection at the customer’s site.
Tip
Currently (6.4 RC), only Ethernet connections are supported in the form of “Interface Legs”.
Interface legs have replaced DHCP, Static, and PPPoE legs. Continued support for mobile broadband USB connections is planned for the full 6.4 release.
Legs can be configured to pass traffic in only one direction, such as having a leg that only contributes to the upload of a bond, not the download. This can be achieved by configuring the speed for the desired direction to 0.
Legs must be dedicated to the bonder. They must not be shared with other devices or networks, because this results in frequent changes in the amount of bandwidth available on the leg (see challenging environments for bonding).
Satellite legs are not supported in any configuration due to their very high latency. The techniques that satellite modems use to accelerate TCP flows cannot be used with SD-WAN because bonded traffic is encapsulated in UDP packets between the bonder and aggregator. This results in very low throughput—for example, less than 100 Kbps on a satellite link with 1.0 Mbps of bandwidth available.
Adding, editing, & deleting legs¶
Legs are displayed in a table on the bond details page.
To add a leg, click the 
button to the upper-left of the legs table. This will open the “add leg” modal.
To edit a leg, click the 
button. This will open the “edit leg” modal.
To delete a leg, click the 
button. This will ask for confirmation, and is permanent.
Leg actions¶
To perform an action on a leg, click the more options icon on the leg action toolbar, and then select the action you want to perform.
Detect MTUs¶
Executes PMTUD to discover the current true path MTU for the leg.
Detect Speeds¶
Begins an automatic speed tuning process for the leg. See the documentation on automatic leg tuning for details.
Renew DHCP Lease¶
Renews the DHCP lease. This action is only available to interface legs with a DHCP address scheme.
Leg status & address information¶
To get comprehensive details on a particular leg’s running state, click the caret 
beside its ID.
This will open the status information dropdown. Here, leg details detected by the bonder at runtime can be found (e.g., the detected path MTU, or a DHCP lease’s length).
Configuring Legs¶
Leg configuration options are accessed through the leg add and edit modals. They are grouped by functionality into the following tabs:
Addresses (Interface Legs Only)
Mobile Broadband (Mobile Broadband Legs Only)
Leg Options¶
Type¶
Currently there are two types of legs:
Interface
Mobile broadband
Type can only be set when creating a new leg.
Link Mode¶
Link mode defines how the leg is used on the bonder and aggregator. This can be one of:
Offline: The leg is not used for anything. The bonder will not bring up this interface at all.
Idle: The leg is configured but not used for bonded traffic. This can be useful if you need to remove a poorly-performing leg from the bond but still want to run ping and throughput tests on it. The bonder may use this leg to connect to the management server.
Active: The leg is configured and used for bonded traffic.
Warning
If all legs are set to offline, your bonder will not be able to contact the management server. For this reason, idle legs are preferred and are not counted for billing.
Provider Profile (Mobile Broadband Legs Only)¶
The provider profile that this leg uses.
Failover¶
If a leg is marked as failover, it will only be used when all the non-failover legs have lost connectivity. At most one leg can be for failover. A typical use case for a failover leg is a wireless connection with high usage-based charges that should only be used as a backup, not as a normal part of the bond.
Download speed¶
The tested download speed that the leg is able to achieve, in Mbps. This field can be set to 0 if this leg is not to be used for download traffic.
Upload speed¶
The tested upload speed that the leg is able to achieve, in Mbps. This field can be set to 0 if this leg is not to be used for upload traffic.
Minimum path MTU¶
If MTU detection is enabled, this value represents the lower bound of the possible MTU values that are checked when detecting the true MTU. This can be increased to speed up the detection process, as long as the value is equal to or lower than any possible MTU for the link. It may also be reduced to accommodate lower MTUs.
Note
The minimum MTU for IPv4 is 576. The minimum MTU for IPv6 is 1280.
Note¶
A free-form field for any relevant information.
Addresses¶
See leg address schemes.
Mobile Broadband¶
IMEI¶
The IMEI (International Mobile Equipment Identity) is a 15-digit unique identifier for a mobile network device, and can be found listed on the device itself and often on the device’s packaging. If the IMEI field is provided, the leg will only use the modem with the given IMEI; if no modem with the given IMEI is attached, the leg will not be started. If the field is not provided, the leg will use any available modem. In general, the IMEI field may be left blank if using a single modem or multiple modems with the same make/model and provider.
Roaming¶
Enabled by default, the roaming option configures whether the leg will be constrained to its home network or not.
SIM PIN¶
The PIN required to access the SIM card, if necessary.
Access modes¶
The list of access modes (2G, 3G, or 4G/LTE) that the modem can use to connect to the mobile network.
Radio bands¶
The list of radio bands (for example, CDMA BC8 1800, DCS, or EUTRAN I) that the modem can use to connect to the mobile network.
Optimization¶
See the leg configuration options for the bandwidth adaptation feature.
Tunnel Bypass¶
See the leg configuration options for the tunnel bypass feature.