Data Center LAN Migration Guide - Juniper Networks

Data Center LAN Migration Guide
• Link-level redundancy in data center networks can be implemented with the following network technologies:
- Link Aggregation Group (LAG)
- Redundant Trunk Groups (RTGs)
- Spanning Tree Protocol (STP) and its variations
- Bidirectional Forwarding Detection (BFD)
- MPLS
We have already discussed LAG, RTG, and STP earlier in this guide. BFD is rapidly gaining popularity in data center
deployments, because it is a simple protocol aiding rapid network convergence (30 to 300 ms resulting in a subsecond
convergence time). BFD is a simple low layer protocol involving a hello mechanism between two devices. The
communication can be across directly connected links or across a virtualized communications path like MPLS.
• Node level resiliency can be achieved using the following technologies:
- Graceful Routing Engine switchover (GRES)
- Graceful restart
- Nonstop active routing (NSR) and nonstop bridging (NSB)
GRES is a feature used to handle planned and unplanned platform restarts gracefully, without any disruptions, by
deploying a redundant Routing Engine in a chassis. The Routing Engines synchronize and share their forwarding state
and configuration. Once synchronized, if the primary Routing Engine fails due to a hardware or software problem, the
secondary Routing Engine comes online immediately, resulting in minimum traffic forwarding interruption.
Rather than being a feature, graceful restart is a standards-based protocol that relies on routing neighbors to
orchestrate and help a restarting router to continue forwarding. There is no disruption in control or in the forwarding
path when the graceful restart node and its neighbors are participating fully and are employing the standard
procedures.
NSR builds on GRES and implements a higher level of synchronization between the Routing Engines. In addition to
the synchronizations and checkpoints between the Routing Engines that GRES achieves, NSR employs additional
protective steps and results in no disruption to the control or data planes, hiding the failure from the rest of the
network. And, it does not require any help from its neighbors to achieve these results. Note that graceful restart and
NSR are mutually exclusive—they are two different means to achieve the same high availability goal.
NSB is similar to GRES and preserves interface and Layer 2 protocol information. In the event of a planned or
unplanned disruption in the primary Routing Engine, forwarding and bridging are continued during the switchover
resulting in minimal packet loss.
Node-level HA includes many aspects, starting with the architecture of the node itself and ending with the protocols
that the node uses to network with other components. Paralleling the Open Systems Interconnection (OSI) Reference
Model, you can view the network infrastructure components starting from the physical layer, which is the node’s
internal architecture and protocols, and ending with the upper tiers, which would include components such as OSPF,
IS-IS, BGP, MPLS, GRES, NSR, etc. No single component provides HA. It is all of the components working together
which creates one architecture and results in high availability.
For more detailed information on HA features on Juniper platforms, refer to: www.juniper.net/techpubs/en_US/
junos10.1/information-products/topic-collections/swconfig-high-availability/frameset.html.
To complement the node-level availability mechanisms highlighted above, devices and systems deployed at critical
points in the data center design should include redundancy of important common equipment such as power supplies,
fans, and Routing Engines at the node levels, so that the procedures mentioned above can have a stable hardware
environment to build upon.
In addition, the software/firmware in these devices should be based on a modular architecture to prevent software
failures or upgrade events from impacting the entire device. There should also be a clean separation between control
plane and data processes to ensure system availability. Junos OS is an example of a multitasking OS that operates in
this manner, ensuring that a failure in one process doesn’t impact any others.
Copyright © 2012, Juniper Networks, Inc. 47