a brief overview on link aggregation ieee 802.3ad

This small presentation gives a very brief overview on link aggregation ieee 802.3ad protocol being used in networking by various organizations, its basics, limitations etc.

1. 1 A brief overview  on “ Link Aggregation - IEEE802.3ad ”

2. Contents What is Link Aggregation? Goals & objectives Static vs. dynamic aggregation(LACP) Working of LACP Limitations Conclusion References 2

3. Definition: Link aggregation Link Aggregation or trunking is a method of combining multiple physical network links into a single logical link to increase the capacity and availability of the communications channel between devices (both switches and end stations) using existing Fast Ethernet and Gigabit Ethernet technology. 3

4. Goals & objectives There are 3 main objectives of link aggregation- Increasing network bandwidth Increasing network availability Load balancing 4

5. Multiple links combined into one logical link. 5 Two switches are shown which are connected using four 1000 Mb/s links. When a higher capacity is needed, the user can group several 1000 Mb/s adapters together to form a high speed connection and this provides migration to 10 Gigabit Ethernet solutions which are not yet available. contd … Increasing bandwidth -:

6. Conditions- Before multiple links can be grouped, some prerequisites must be met. All links must- be in full duplex mode, have the same data rate (usually 1 Gbps ) connect to precisely one endpoint on a switch or server Addressing- A standard IEEE802.3 MAC address is assigned to system, aggregator & each port. The MAC client “see” the aggregator MAC address. 6

7. Since multiple links connect two devices, even if one fails the other links keep carrying the information and the traffic on the failed link is also transferred to them. 7 The loss of a link within an aggregation reduces the available capacity but the connection is maintained and the data flow is not interrupted. Increasing availability -:

8. Hardware load balancer provides WAN aggregation. 8 A ggregating multiple Internet access lines for increased performance and reliability. With the load balancer, multiple DSL, cable modem or USB modems can be combined to provide higher speed and more reliable Internet access.  Load balancing -:

9. Static vs. Dynamic link aggregation Static link aggregation- With a static link aggregation, all configuration settings will be setup on both participating LAG components. For static aggregated links (the default port setting for link aggregation is static), the linked Switches must be manually configured and do not allow dynamic changes to the aggregated port group. 9

10. Dynamic link aggregation: Link aggregation Control Protocol (LACP)- LACP allows a network device to negotiate an automatic bundling of links by sending LACP packets to the peer (directly connected device that also implements LACP). The main purpose of LACP is to automatically add/delete individual links to the aggregate bundle, while adding new links and also after recovering from link failures. LACP can monitor to verify if all the links are connected to the right group. 10 contd …

11. LACP is a dynamic protocol. It is sufficient if multiple ports on various devices are LACP enabled, once. LACP is a standard and hence LACP can be implemented between multi-vendor switches. 11

12. How LACP works? 12 The LACP protocol involves the exchange of LACPDUs between the devices at either end of an Ethernet link. f ig: LACPDU frame structure contd …

13. When LACP is enabled on the switch, all ports come under LACP control by default . LACP controlled ports can be in one of two modes, either Active or Passive . In active mode- When we enable LACP, it will send LACPDUs down each 'Active mode' connected link to find any partners that also have LACP enabled. If a reply is received, the device builds up a database of which link goes to which partner device. When LACP detects that two or more links are connected to the same partner device, it will aggregate them into one logical link. Any further physical links added to the same partner system will simply be added to the now existing trunk group (within physical bounds ). In passive mode- The same actions will take place if a port is in passive mode and it receives a LACP control packet - it will build a database of connected partners and begin sending control packets out that interface. 13

14. Limitations Half-duplex operation – supported only on point-to-point links with MACs operating in full duplex mode. Multiple data rates – All Links in a Link Aggregation Group operate at the same data rate (e.g. 10 Mb/s, 100 Mb/s or 1000 Mb/s ) Redundancy limit – Link Aggregation accounts for only cabling failures but does not give redundancy in the case of switch failures (although some proprietary vendor implementations can achieve this ). Ports upper bound – There is a maximum limit to the number of links in each Link Aggregation Group (LAG) and it is generally specified by the vendor (generally eight). 14

15. Conclusion Link aggregation provides two fundamental benefits: increased capacity and increased resiliency. Scalable performance and high system availability are critical to today’s enterprises. Although work on the IEEE 802.3ad link aggregation standard is well under way, several vendors, have chosen to implement prestandard versions of this technology to meet immediate customer demand. Over the next few years, serial link aggregation is likely to become one of the key design methods that high-performance system designers use to cost-effectively meet the increasing need to support higher data bandwidths within their applications. 15

16. References World Wide Web www.wikipedia.org Research paper on ‘ Conceptual framework of redundant link aggregation’ by Rafiullah Khan and Shaukat Ali  Research paper on ‘Multiple Systems Link Aggregation Control Protocol’ by Rick van ‘t  Spijker     Research paper on ‘Link Aggregation –IEEE 802 3ad’ by Fulvio Risso & Politecnico di Torino 16