Link Aggregation · Topic 2 of 2

Bonding Compatibility with Static Link Aggregation

Match RouterOS bonding modes to other vendor port groups, such as static EtherChannel and LACP, and learn how to verify and troubleshoot a bond.

4 min

In a nutshell

802.3ad pairs with LACP, and static modes pair with a static group.
balance-xor is the usual match for EtherChannel in on mode.
PAgP is Cisco only and does not work with RouterOS bonding.

What it is

A bond only works when both ends use a compatible method, so you must match the RouterOS mode to the other device.

Different vendors use different names for the same ideas. A static group, a port channel in on mode and a manual trunk all mean the same thing: links are bundled without any negotiation.

This page shows which pairs work, and how to check them.

How it works

Static modes need a static group on the other side, and dynamic mode needs LACP.

Static link aggregation

A static group has no protocol. The ports are simply forced together.

The switch hashes outgoing traffic over the member ports and accepts incoming traffic on any member. Nothing checks that the other end agrees. This is fast to set up but easy to get wrong, because a mistake at one end causes loops or loss, with no warning.

Matching table

Use this table to choose the pair.

RouterOS mode	Other device	Works
`802.3ad`	LACP group, active or passive	Yes
`balance-xor`	Static group, such as EtherChannel in `on` mode	Yes
`balance-rr`	Static group	Yes, but packets may be reordered
`broadcast`	Static group	Yes, rarely used
`active-backup`	Plain ports with no group	Yes
`balance-tlb`, `balance-alb`	Plain ports with no group	Yes
`802.3ad`	Static group with no LACP	No
Static modes	LACP group	No

Cisco style groups

Cisco calls a bundle an EtherChannel, with three ways to build it.

LACP, modes active and passive: matches RouterOS 802.3ad.
Static, mode on: matches RouterOS balance-xor, or balance-rr.
PAgP: a Cisco only protocol, and it does not interoperate with RouterOS bonding.

If the other side uses PAgP, you must change that side to LACP or to static, or use a bond mode that needs no group.

Hash alignment

Each end decides the spread of its own outgoing traffic.

The two directions can use different hash methods. A bond that sends with layer-3-and-4 can talk to a switch that hashes on MAC addresses. Pick the hash that gives a good spread for your traffic on each device separately.

Bonding with bridges and VLANs

A bond can be a bridge port, and VLANs can run over it.

/interface bridge port add bridge=bridge1 interface=bond1
/interface bridge vlan add bridge=bridge1 vlan-ids=10,20 tagged=bond1

The bond is then one logical port for spanning tree, and for VLAN filtering. The member interfaces should not be bridge ports themselves. Put the bond in the bridge, not its slaves.

On some switch chips a bond in a bridge can be hardware offloaded, but only for certain modes. Check the offload flag on the bridge port after configuring it.

Verifying a bond

/interface bonding print
/interface bonding monitor bond1
/interface bridge port print

The monitor shows which slaves are active and which are not. For 802.3ad, it also shows information from the partner. If a slave is inactive, check the cable, the mode on the other side, and the speed and duplex of each member.

Typical faults

A mode mismatch, such as 802.3ad against a static group.
A slave left as a separate bridge port.
Different speeds on the slaves.
A static group on one side only, which causes a loop or flapping MAC addresses.

Watch out

A static group configured on one end only can create a loop, because the other end sees separate links.

What to remember for the exam

Seven facts cover most questions on this topic.

802.3ad pairs with LACP, and static modes pair with a static group.
balance-xor is the usual match for EtherChannel in on mode.
PAgP is Cisco only and does not work with RouterOS bonding.
active-backup, balance-tlb and balance-alb need no group on the other side.
Each side chooses its own transmit hash.
Put the bond in the bridge, and not its slave interfaces.
/interface bonding monitor shows the active and inactive slaves.

Exam tip

Configure both ends before you connect all cables. Connecting first can create a short loop.

Common mistakes

These four mistakes appear often.

Mixing LACP and static. One end waits for LACP messages, and the other never sends them.

Choosing PAgP. RouterOS cannot speak it, so use LACP or static.

Leaving slaves in the bridge. A slave in the bridge and in the bond breaks forwarding.

Mismatched speed. One slow member limits the group, or is left out.

Check yourself

Work through these three questions.

Which RouterOS mode matches an EtherChannel in on mode?
balance-xor, because both ends use a static group.
Can RouterOS bonding form a bundle with PAgP?
No, because PAgP is Cisco only and RouterOS does not support it.
Which command shows active and inactive slaves?
/interface bonding monitor bond1.

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