No relevant resource is found in the selected language.

This site uses cookies. By continuing to browse the site you are agreeing to our use of cookies. Read our privacy policy>Search

Reminder

To have a better experience, please upgrade your IE browser.

upgrade

Configuration Guide - Low Latency Network

CloudEngine 8800, 7800, 6800, and 5800 V200R005C00

This document describes the configurations of Buffer optimization of lossless queues, Fast ECN, Fast CNP, Dynamic ECN threshold of lossless queues, and Dynamic load balancing.
Rate and give feedback :
Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Dynamic Load Balancing

Dynamic Load Balancing

NOTE:

Only the CE6865EI and CE8850-64CQ-EI support this function.

Background

A flow refers to data packets with the same feature fields and is divided into multiple flowlets based on a specific interval.

As shown in Figure 2-9, the LAG and ECMP generally use the per-flow load sharing mechanism. This mechanism uses the hash algorithm to generate hash key values with the feature fields (including the source MAC address, destination MAC address, and IP 5-tuple) of data packets as hash factors and selects one of multiple load-balanced links to forward data packets. Data packets with different feature fields may have different hash key values and therefore are forwarded through different member links. Data packets with the same feature fields have the same hash key value and are forwarded through the same member link. This load balances flows forwarded on different member links and ensures the correct sequence of data packets in a flow.

This load balancing mode based on feature fields of data packets is also referred to as the static load balancing mode. However, this mode does not take into account the usage of each member link, and the loads of member links may be unbalanced. In particular, when there are large flows, congestion or even packet loss may occur on member links.

Figure 2-9 Static load balancing

Dynamic load balancing can resolve the preceding issues. During data packet forwarding, this mechanism checks the usage of each member link and selects a member link with the lightest load to forward data packets.

Implementation

Dynamic load balancing supports three modes: eligible, spray, and fixed. The eligible dynamic load balancing mode is recommended.

  • Eligible dynamic load balancing

    A transmission delay exists on links between two devices that are directly connected. If the interval for sending data packets is longer than the maximum transmission delay on links that are load balanced, data packets arrive at the receive end in the correct sequence when they are transmitted through different member links.

    The eligible load balancing mode is implemented based on this principle. In this mode, when forwarding a data packet, the device determines the interval between forwarding the current data packet and the previous one in the same flow. If the interval is greater than the maximum transmission delay on links that are load balanced, the data packet to be forwarded is the first packet of a new flowlet. If the interval is less than the maximum transmission delay, the data packet is forwarded in the same flowlet as the previous packet. Based on the flowlet, a device selects a member link with the lightest load to forward the data packet. Data packets in the same flowlet are forwarded through the same link.

    Figure 2-10 Eligible dynamic load balancing mode
    Using Figure 2-10 as an example, the following describes the implementation of the eligible dynamic load balancing mode:
    1. Data packet 1 is the first packet of Flow1. When receiving data packet 1, SwitchA detects that it is the first packet of a new flowlet (Flowlet1-1) and selects one of the two load-balanced links (that with the lightest load) to forward this data packet. Member links 1 and 2 have the same load (zero), so either of them can be selected. Assume that member link 1 is selected.
    2. When receiving data packet 2, SwitchA detects that the interval between data packets 1 and 2 is less than the maximum transmission delay and forwards data packet 2 in the same flowlet as data packet 1 through the same link (member link 1).
    3. When receiving data packet 3, SwitchA detects that the interval between data packets 2 and 3 is less than the maximum transmission delay and forwards data packet 3 in the same flowlet as data packet 2 through the same link (member link 1).
    4. Data packet 4 is the first packet of Flow2. When receiving data packet 4, SwitchA detects that it is the first packet of a new flowlet (Flowlet2-1) and selects a member link with a lighter load (member link 2) to forward this data packet.
    5. When receiving data packet 5, SwitchA detects that the interval between data packets 4 and 5 is less than the maximum transmission delay and forwards data packet 5 in the same flowlet as data packet 4 through the same link (member link 2).
    6. When receiving data packet 6, SwitchA detects that the interval between data packets 3 and 6 is greater than the maximum transmission delay, indicating that data packet 6 is the first packet of a new flowlet (Flowlet1-2). Then SwitchA forwards data packet 6 through a link with a lighter load (member link 2).
    7. When receiving data packet 7, SwitchA detects that the interval between data packets 6 and 7 is less than the maximum transmission delay and forwards data packet 7 in the same flowlet as data packet 6 through the same link (member link 2).
  • Spray dynamic load balancing mode

    The spray dynamic load balancing mode uses the per-packet load sharing mechanism. That is, a device forwards a data packet through one of several load-balanced links. In this mechanism, if the interval between two neighboring data packets in the same flow is less than the maximum transmission delay on links that are load balanced and the data packets are forwarded through different links, the two packets are received out of order. If this mode is used, the device must support packet reassembly to cope with packet mis-sequencing.

    Figure 2-11 Spray dynamic load balancing mode
    Using Figure 2-11 as an example, the following describes the implementation of the spray dynamic load balancing mode. Assume that data packets 1, 2, 4, and 5 are of the same size and data packet 3 is 4 times the size of the other packets.
    1. When receiving data packet 1, SwitchA selects one of the two load-balanced links (that with the lightest load) to forward this data packet. Member links 1 and 2 have the same load (zero), so either of them can be selected. Assume that member link 1 is selected.
    2. When receiving data packet 2, SwitchA selects a member link with a lighter load (member link 2) to forward this data packet.
    3. When receiving data packet 3, SwitchA selects a member link with a lighter load (member link 1) to forward this data packet.
    4. When receiving data packet 4, SwitchA selects a member link with a lighter load (member link 2) to forward this data packet.
    5. When receiving data packet 5, SwitchA selects a member link with a lighter load (member link 2) to forward this data packet.

    In this case, packets 2 and 4 arrive at SwitchB before packet 3, causing packet mis-sequencing.

  • Fixed dynamic load balancing mode

    In fixed dynamic load balancing mode, a device forwards a data packet through the link that forwarded the previous data packet. If the data packet to be forwarded is the first packet in a flow, the device forwards it through one of the member links in static load balancing mode based on the hash result.

    Figure 2-12 Fixed dynamic load balancing mode
    Using Figure 2-12 as an example, the following describes the implementation of the fixed dynamic load balancing mode:
    1. When receiving data packet 1, SwitchA selects one of the member links in static load balancing mode to forward this data packet based on the hash result. Assume that member link 1 is selected.
    2. When receiving data packet 2 that is in the same flow as the previous packet (data packet 1), SwitchA selects member link 1 to forward this data packet.
    3. When receiving data packet 3, SwitchA detects that it is the first packet of Flow2 and forwards it through one of the member links in static load balancing mode based on the hash result. Assume that member link 2 is selected.
    4. When receiving data packet 4 that is in the same flow as the previous packet (data packet 2), SwitchA selects member link 1 to forward this data packet.
Translation
Download
Updated: 2019-04-20

Document ID: EDOC1100040243

Views: 5519

Downloads: 100

Average rating:
This Document Applies to these Products
Related Documents
Related Version
Share
Previous Next