Simple Queues, Target, Limits and Bursting

What it is

A simple queue limits the bandwidth of a host, a network or an interface.

Without a queue, hosts on a LAN compete for the Internet link, and one busy host can slow all the others. A queue sets a ceiling for a target, and it can also promise a minimum.

The simple queue is the easiest queue type on RouterOS. One entry holds the target, the limits and the burst options in one place.

How it works

The queue matches traffic by target, applies the limits for each direction, and can allow short bursts.

Creating a simple queue

/queue simple add name=lan-limit target=192.168.88.0/24 max-limit=10M/20M
/queue simple print

The name is only a label. The target says whose traffic the queue controls. The max-limit sets the ceiling.

Speeds can use suffixes such as k for kilobits and M for megabits per second.

Target

The target is the address, the network or the interface that the queue applies to. It can be a single host, a subnet, or a list of them.

A queue with a target of one subnet treats the whole subnet as one group. All hosts in the group share the limit. A queue with a single host address limits only that host.

The target is seen from the point of view of the LAN host. Traffic that the target sends is upload, and traffic that the target receives is download.

Destinations

By default a queue matches traffic between the target and any destination. The dst setting narrows this to traffic towards a chosen destination.

/queue simple add name=to-internet target=192.168.88.0/24 dst=ether1 max-limit=10M/20M

With dst=ether1, only traffic that goes out through the WAN interface is limited. Traffic between LAN hosts is not touched. This is often what you want, because a LAN should not be throttled to the speed of the Internet link.

The destination can also be an address or a network. Use it to give different limits to different directions, such as one limit for a local server and another for the Internet.

Max-limit and limit-at

Two settings give the queue its shape. Each takes two values, written as upload/download.

/queue simple add name=office target=192.168.88.0/24 limit-at=2M/2M max-limit=10M/10M

In this example the office is guaranteed 2 Mbit/s each way and may use up to 10 Mbit/s when the link has room. A guarantee only makes sense when the link is busy. If the link is idle, the target can take as much as the ceiling allows.

If you set only max-limit, the target has a ceiling and no guarantee. When several queues compete, the ones with a guarantee are served first.

Bursting

Bursting lets a target go above its normal limit for a short time. It helps web browsing, where pages load in short spurts.

/queue simple add name=user1 target=192.168.88.10 max-limit=2M/2M burst-limit=4M/4M burst-threshold=1500k/1500k burst-time=20s/20s

The router measures the average rate over burst-time. While that average stays below burst-threshold, the target may burst up to burst-limit. When the average reaches the threshold, the rate falls back to max-limit.

Note that burst-time is the averaging period and not the length of the burst. A burst ends when the average catches up with the threshold.

The burst threshold should sit below max-limit, and the burst limit above it.

Order of queues

Simple queues are checked from the top of the list. A packet is handled by the first queue that matches, so the order of entries matters.

Place specific queues for single hosts above general queues for whole subnets. Otherwise the subnet queue catches the packet first, and the host queue never sees it.