Upcoming Events

Where the Cloud Touches Down: Simplifying Data Center Infrastructure Management

Thursday, July 25, 2013
10:00 AM PT/1:00 PM ET

In most data centers, DCIM rests on a shaky foundation of manual record keeping and scattered documentation. OpManager replaces data center documentation with a single repository for data, QRCodes for asset tracking, accurate 3D mapping of asset locations, and a configuration management database (CMDB). In this webcast, sponsored by ManageEngine, you will see how a real-world datacenter mapping stored in racktables gets imported into OpManager, which then provides a 3D visualization of where assets actually are. You'll also see how the QR Code generator helps you make the link between real assets and the monitoring world, and how the layered CMDB provides a single point of view for all your configuration data.

Register Now!

A Network Computing Webinar:
SDN First Steps

Thursday, August 8, 2013
11:00 AM PT / 2:00 PM ET

This webinar will help attendees understand the overall concept of SDN and its benefits, describe the different conceptual approaches to SDN, and examine the various technologies, both proprietary and open source, that are emerging. It will also help users decide whether SDN makes sense in their environment, and outline the first steps IT can take for testing SDN technologies.

Register Now!

More Events »

Subscribe to Newsletter

  • Keep up with all of the latest news and analysis on the fast-moving IT industry with Network Computing newsletters.
Sign Up

Crash Course: Router Redundancy Protocols

Another trade-off is that, though an OSPF-based device can immediately reroute traffic upon detecting a downed link, it may not always get the information. If you have another firewall or switch between your core router and the aggregator switch, for example, and the router goes down, the link state will not change on the aggregator switch because it is not directly connected. Then you're dependent on OSPF's "hello" protocol, which checks the status of its neighbors. By default, a hello message is sent every 10 seconds and when four replies are missed, OSPF considers the neighboring device down.

It's best to have direct connections to avoid this; you can even change the default timer settings to provide faster convergence. You may also have to pay extra to add OSPF to aggregator switches, as some vendors only provide it as an option.

You can remove more single points of failure as you work toward the edge of the network. You can, for instance, connect each workgroup switch to dual aggregator switches, so if one switch crashes, you'll have a backup. This also means each workgroup switch will need dual connections--one to each switch--which adds further redundancy. You should have four cables, usually fiber, depending upon the distance, going from the core to each pair of aggregator switches.

A simple way to add redundancy between any two switches is to use the IEEE 802.3ad protocol. This trunking protocol takes multiple connections and combines them into one virtual pipe, to increase bandwidth. Packets are load-balanced across the connections so, if one of them goes down, traffic is directed to the remaining connection or connections.

The downside of 802.3ad is there has to be a connection between two switches--you cannot have two connections on one switch going to two different switches. You can, however, have two connections from an aggregator switch to two different cards on the core switch, which at least gives you redundancy at both the card and port levels. Some vendors let you use 802.3ad at the aggregator switch and plug into two different core switches that emulate one switch.

Page: « Previous Page | 123 4 | 567  | Next Page »

Related Reading

More Insights

Network Computing encourages readers to engage in spirited, healthy debate, including taking us to task. However, Network Computing moderates all comments posted to our site, and reserves the right to modify or remove any content that it determines to be derogatory, offensive, inflammatory, vulgar, irrelevant/off-topic, racist or obvious marketing/SPAM. Network Computing further reserves the right to disable the profile of any commenter participating in said activities.

Disqus Tips To upload an avatar photo, first complete your Disqus profile. | Please read our commenting policy.
Vendor Comparisons
Network Computing’s Vendor Comparisons provide extensive details on products and services, including downloadable feature matrices. Our categories include:

Research and Reports

Network Computing: April 2013

TechWeb Careers