computer science

IEEE 802.1aq

IEEE 802.1aq is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand IEEE 802.1aq rather than just read about it. In short: IEEE 802.1aq is an amendment to the IEEE 802.1Q networking standard which adds support for Shortest Path Bridging (SPB). This technology is intended to simplify the creation and configuration of Ethernet networks while enabling multipath routing.

Key takeaways

IEEE 802.1aq belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect IEEE 802.1aq to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of IEEE 802.1aq from memory before moving on to harder problems.

Reference excerpt

IEEE 802.1aq is an amendment to the IEEE 802.1Q networking standard which adds support for Shortest Path Bridging (SPB). This technology is intended to simplify the creation and configuration of Ethernet networks while enabling multipath routing. SPB is designed to replace the older Spanning Tree Protocols: IEEE 802.1D STP, IEEE 802.1w RSTP, and IEEE 802.1s MSTP. These block any redundant paths that can result in a switching loop, whereas SPB allows all paths to be active with multiple equal-cost paths, provides much larger layer-2 topologies, supports faster convergence times, and improves the efficiency by allowing traffic to load share across all paths of a mesh network. It is designed to preserve the plug-and-play nature that established Ethernet as the de facto protocol at layer 2. The technology provides VLANs on native Ethernet infrastructures using a link-state protocol to advertise both topology and VLAN membership. Packets are encapsulated at the edge either in MAC-in-MAC per IEEE 802.1ah or tagged per IEEE 802.1Q or IEEE 802.1ad and transported only to other members of VLAN. Unicast, multicast, and broadcast are supported and all routing is on symmetric shortest paths. The control plane is based on the Intermediate System to Intermediate System (IS-IS) routing protocol, leveraging a small number of extensions defined in RFC 6329.

History On 4 March 2006 the working group posted 802.1aq draft 0.1. In March 2012 the IEEE approved the 802.1aq standard. In May 2013, the first public multivendor interoperability was demonstrated as SPB served as the backbone for Interop 2013 in Las Vegas. In 2013 and 2014 SPB was used to build the InteropNet backbone with only one-tenth the resources of prior years. During Interop 2014 SPB was used as the backbone protocol which can enable software-defined networking (SDN) functionalities. The 2014 Winter Olympics were the first "fabric-enabled" Games using SPB "IEEE 802.1aq" technology. During the games this fabric network could handle up to 54 Tbit/s of traffic.

Associated protocols IEEE 802.1Q-2014 - Bridges and Bridged Networks - This standard incorporates Shortest Path Bridging (IEEE 802.1aq) with the following: IEEE Std 802.1Q-2011, IEEE Std 802.1Qbe-2011, IEEE Std 802.1Qbc-2011, IEEE Std 802.1Qbb-2011, IEEE Std 802.1Qaz-2011, IEEE Std 802.1Qbf-2011, IEEE Std 802.1Qbg-2012, IEEE Std 802.1Q-2011/Cor 2–2012, and IEEE Std 802.1Qbp-2014, and much functionality previously specified in 802.1D. IEEE 802.1ag - Connectivity Fault Management (CFM) IEEE 802.1Qbp - Equal Cost Multiple Paths in Shortest Path Bridging IEEE P802.1Qcj - Automatic Attachment to Provider Backbone Bridging (PBB) services RFC 6329 - IS-IS Extensions Supporting IEEE 802.1aq Shortest Path Bridging

RFC 6329 The Intermediate System to Intermediate System (IS-IS) protocol, as defined in the IETF proposed standard RFC 6329, is used as the control plane for SPB. SPB requires no state machine or other substantive changes to IS-IS, and simply requires a new Network Layer Protocol Identifier (NLPID) and set of TLVs. SPB allows for shortest-path forwarding in a mesh-connected Ethernet network utilizing multiple equal-cost paths. This permits SPB to support large Layer 2 topologies, with faster convergence, and improved use of the mesh topology when compared to networks configured with Spanning Tree Protocol. SPB augments IS-IS with a small number of TLVs and sub-TLVs, and supports two Ethernet-encapsulating data paths, IEEE 802.1ad provider bridges (PB) and IEEE 802.1ah Provider Backbone Bridges (PBB). SPB is designed to run in parallel with other network-layer protocols such as IPv4 and IPv6. Standards mandate that the failure of two nodes to establish an SPB adjacency will not have a collateral impact, such as the rejection of an adjacency for other network-layer protocols (e.g., OSPF).

Protocol extensions The IS-IS extensions defined in RFC 6329 that deliver standardized support for 802.1aq SPB are:

IS-IS Hello (IIH) Protocol Extensions Node Information Extensions Adjacency Information Extensions Service Information Extensions

IS-IS Hello (IIH) protocol extensions 802.1aq has been designed to operate in parallel with other network layer protocols such as IPv4 and IPv6; therefore, failure of two nodes to establish an SPB adjacency will not cause network layer protocols to also reject an adjacency. RFC 6328 assigns 802.1aq the Network Layer Protocol ID (NLPID) value 0xC1. This NLPID is used by SPB Bridges to indicate their ability to form adjacencies and operate as part of an 802.1aq domain. 802.1aq frames flow on adjacencies that advertise this NLPID in both directions, and nodes regard an adjacency that has not been advertised in both directions as non-existent (with infinite link metric). 802.1aq augments the normal IIH PDU with three new TLVs, which, like all other SPB TLVs, travel within Multi-Topology TLVs, therefore allowing multiple logical instances of SPB within a single IS-IS protocol instance. SPB can use many VIDs, agreeing on which VIDs are used for which purposes. The IIH PDUs carry a digest of all the used VIDs, referred to as the Multiple Spanning Tree Configuration TLV, which uses a common and compact encoding reused from IEEE 802.1Q. For the purposes of loop prevention, SPB neighbors may also support a mechanism to verify that the contents of their topology databases are synchronized. Exchanging digests of SPB topology information, using the optional SPB-Digest sub-TLV, allows nodes to compare information and take specific action where a mismatch in topology is indicated. Finally, SPB needs to know which shortest path tree (SPT) sets are being used by which VIDs, and this is carried in the Base VLAN Identifiers TLV.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with IEEE 802.1aq

Start with the simplest possible case. Write down what IEEE 802.1aq claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to IEEE 802.1aq before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about IEEE 802.1aq ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of IEEE 802.1aq

In research: IEEE 802.1aq appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses IEEE 802.1aq in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: IEEE 802.1aq is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ethernet standards, IEEE 802, Internet architecture, so understanding it makes those chapters shorter.
In everyday life: Look for IEEE 802.1aq outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study IEEE 802.1aq in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what IEEE 802.1aq means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain IEEE 802.1aq out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is IEEE 802.1aq in simple terms?

Why does IEEE 802.1aq matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study IEEE 802.1aq?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on IEEE 802.1aq.