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Understanding Multicast Load Balancing on Aggregated 10-Gigabit Links for Routed Multicast Traffic on EX8200 Switches
Streaming video technology was introduced in 1997. Multicast protocols were subsequently developed to reduce data replication and network overloads. With multicasting, servers can send a single stream to a group of recipients instead of sending multiple unicast streams. While the use of streaming video technology was previously limited to occasional company presentations, multicasting has provided a boost to the technology resulting in a constant stream of movies, real-time data, news clips, and amateur videos flowing nonstop to computers, TVs, tablets, and phones. However, all of these streams quickly overwhelmed the capacity of network hardware and increased bandwidth demands leading to unacceptable blips and stutters in transmission.
To satisfy the growing bandwidth demands, multiple links were virtually aggregated to form bigger logical point-to-point link channels for the flow of data. These virtual link combinations are called multicast interfaces, also known as link aggregation groups (LAGs).
Multicast load balancing involves managing the individual links in each LAG to ensure that each link is used efficiently. Hashing algorithms continually evaluate the data stream, adjusting stream distribution over the links in the LAG, so that no link is underutilized or overutilized. Multicast load balancing is enabled by default on Juniper Networks EX8200 Ethernet Switches.
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Create LAGs for Multicasting in Increments of 10 Gigabits
The maximum link size on an EX8200 switch is 10 gigabits. If you need a larger link on an EX8200 switch, you can combine up to twelve 10-gigabit links. In the sample topology shown in Figure 1, four 10-gigabit links have been aggregated to form each 40-gigabit link.
Figure 1: 40-Gigabit LAGs on EX8200 Switches
When Should I Use Multicast Load Balancing?
Use a LAG with multicast load balancing when you need a downstream link greater than 10 gigabits. This need frequently arises when you act as a service provider or when you multicast video to a large audience.
To use multicast load balancing, you need the following:
- An EX8200 switch—Standalone switches support multicast load balancing, while Virtual Chassis does not.
- A Layer 3 routed multicast setup—For information about configuring multicasting, see Junos OS Routing Protocols Configuration Guide.
- Aggregated 10-gigabit links in a LAG—For information about configuring LAGs with multicast load balancing , see Configuring Multicast Load Balancing for Use with Aggregated 10-Gigabit Ethernet Links on EX8200 Switches (CLI Procedure).
How Does Multicast Load Balancing Work?
Juniper Networks Junos operating system (Junos OS) supports the Link Aggregation Control Protocol (LACP), which is a subcomponent of IEEE 802.3ad. LACP provides additional functionality for LAGs and is supported only on Layer 3 interfaces. When traffic can use multiple member links, traffic that is part of the same stream must always be on the same link.
Multicast load balancing uses one of seven available hashing algorithms and a technique called queue shuffling (alternating between two queues) to distribute and balance the data, directing streams over all available aggregated links. You can select one of the seven algorithms when you configure multicast load balancing, or you can use the default algorithm, crc-sgip, which uses a cyclic redundancy check (CRC) algorithm on the multicast packets’ group IP address. We recommend that you start with the crc-sgip default and try other options if this algorithm does not evenly distribute the Layer 3 routed multicast traffic. Six of the algorithms are based on the hashed value of IP addresses (IPv4 or IPv6) and will produce the same result each time they are used. Only the balanced mode option produces results that vary depending on the order in which streams are added. See Table 1 for more information.
Table 1: Hashing Algorithms Used by Multicast Load Balancing
Hashing Algorithms | Based On | Best Use |
|---|---|---|
crc-sgip | Cyclic redundancy check of multicast packets’ source and group IP address | Default—high-performance management of IP traffic on 10-Gigabit Ethernet network. Predictable assignment to the same link each time. This mode is complex but yields a good distributed hash. |
crc-gip | Cyclic redundancy check of multicast packets’ group IP address | Predictable assignment to the same link each time. Try this mode when crc-sgip does not evenly distribute the Layer 3 routed multicast traffic and the group IP addresses vary. |
crc-sip | Cyclic redundancy check of multicast packets’ source IP address | Predictable assignment to the same link each time. Try this mode when crc-sgip does not evenly distribute the Layer 3 routed multicast traffic and the stream sources vary. |
simple-sgip | XOR calculation of multicast packets’ source and group IP address | Predictable assignment to the same link each time. This is a simple hashing method that might not yield as even a distribution as crc-sgip yields. Try this mode when crc-sgip does not evenly distribute the Layer 3 routed multicast traffic. |
simple-gip | XOR calculation of multicast packets’ group IP address | Predictable assignment to the same link each time. This is a simple hashing method that might not yield as even a distribution as crc-gip yields. Try this when crc-gip does not evenly distribute the Layer 3 routed multicast traffic and the group IP addresses vary. |
simple-sip | XOR calculation of multicast packets’ source IP address | Predictable assignment to the same link each time. This is a simple hashing method that might not yield as even a distribution as crc-sip yields. Try this mode when crc-sip does not evenly distribute the Layer 3 routed multicast traffic and stream sources vary. |
balanced | Round-robin calculation method used to identify multicast links with the least amount of traffic | Best balance is achieved, but you cannot predict which link will be consistently used because that depends on the order in which streams come online. Use when consistent assignment is not needed after every reboot. |
How Do I Implement Multicast Load Balancing on an EX8200 Switch?
To implement multicast load balancing with an optimized level of throughput on an EX8200 switch, follow these recommendations:
- Allow 25 percent unused bandwidth in the aggregated link to accommodate any dynamic imbalances due to link changes caused by sharing multicast interfaces.
- For downstream links, use multicast interfaces of the same size whenever possible. Also, for downstream aggregated links, throughput is optimized when members of the aggregated link belong to the same devices.
- For upstream aggregated links, use a Layer 3 link whenever possible. Also, for upstream aggregated links, throughput is optimized when the members of the aggregated link belong to different devices.
