A Journey Through Network Evolution — Part 5: BONUS for Link Aggregation Groups.
Proprietary Links Aggregation Groups
Vendor-specific LAG technologies offer tailored solutions to network challenges, leveraging proprietary protocols and configurations. These implementations cater to specific network environments, addressing unique requirements with precision. For instance, Cisco’s Flex Links and Juniper’s Redundant Trunk Groups are prime examples of such proprietary solutions.
Both Cisco Flex Links and Juniper Trunk Groups provide rapid convergence in the event of link failures, ensuring seamless connectivity and minimal downtime. Basically, they’re using a pair of Layer 2 interfaces (physical or aggregated) and combining them into a single logical interface by designating one link as primary and another as backup. This enables fast failover without the need for complex configurations.
Both protocols are typically configured in service-provider or enterprise networks where customers do not want to run STP. That is the main reason why none of the STP protocols can run on this link aggregation group interfaces (as we don’t need STP in this case). While Cisco and Juniper solutions support a maximum of 16 Flex Links / RTGs, Juniper high-end switches EX8200 support up to 254 redundant trunk groups (EX8200 is EOL by the way).
Examples
As an example in a corporate network, Cisco Flex Links and Juniper RTG help maintain uninterrupted connectivity between critical network segments. When a primary link experiences issues, traffic is rerouted to the backup link, ensuring seamless operations.
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There is some sort of specific behaviour I’ve noticed in both Cisco and Juniper implementations. For example, Cisco Flex Links documentation states that “Local administrative shut down or a link that starts forwarding again due to pre-emption is not considered a link failure. In those cases, the feature flushes the dynamic hosts and does not move them”.
In Juniper RTG implementation I’ve found that “Data traffic on the secondary link is dropped and shown as dropped packets when you issue the operational mode command show interfaces interface-name extensive” and “While data traffic is blocked on the secondary link, Layer 2 control traffic is still permitted”.
Benefits
In a typical enterprise network composed of distribution and access layers, a redundant trunk link provides a simple solution for trunk interface network recovery. When a trunk interface fails, data traffic is routed to another trunk interface after one second, thereby keeping network convergence time to a minimum. Compared to STP protocol, this greatly impacts critical services as even when tuned and optimized STP has a recovery delay of up to 50 seconds from a broken link to the forwarding state. Cisco FlexLink+ (came after the deprecation of the Cisco Flex Links and using REP for loop control) even provides convergence time between 10–90 msecs, which will not affect most of the usually used services overall.
Limitations
As far as you may notice, these proprietary protocols have caveats and limitations as well. First of all, the main limitation is — being proprietary. That means that you can’t simply expand these protocols across your network if it’s multivendor. Secondarily, both protocols provide only link failure redundancy and don’t provide any traffic distribution or load-balancing across multiple links (FlexLink+ actually brings this feature onboard and supports VLAN load-balancing). That means you always have unused links which brings additional operational overhead in running your network. If you want to evenly distribute the traffic across all connected links and utilize them all, look to the standardized LAG implementations such as LACP or even STP (MSTP in Cisco or VSTP in Juniper).
Conclusion
In conclusion, vendor-specific Link Aggregation Group technologies offer tailored solutions to network challenges, addressing unique requirements with precision. Cisco Flex Links and Juniper Redundant Trunk Groups exemplify this approach, providing rapid failover and enhanced redundancy but lacking in efficiency of traffic distribution and multivendor compatibility. As we continue our journey through network evolution, let’s cautiously leverage these proprietary technologies to build resilient and high-performance networks. Join us in exploring the next frontier of network technology and unlocking the full potential of Link Aggregation Groups!
Stay tuned for more insights and updates as we delve deeper into the world of network evolution. Share your thoughts, questions, and experiences in the comments below, and let’s continue this tech odyssey together!
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