Crash Course: Router Redundancy Protocols
April 18, 2006
Peter Morrissey is a faculty member of Syracuse University's School of Information Studies, and a contributing editor and columnist for Network Computing. Write to him at firstname.lastname@example.org.
Router vendors offer proprietary solutions that may provide quicker and more efficient failover schemes than standard protocols. And a single-vendor solution can help avoid finger-pointing after an outage.
Extreme Networks' EAPS (Ethernet Automatic Protection Switching) protocol is the only one designed to fail over within 50 ms. Individual rings can be configured for each aggregator-to-core connection. Foundry Networks also has a proprietary redundancy solution and is working to implement the IETF's BFD (Bidirectional Forwarding Detection) draft protocol, to detect failures more quickly than existing standards when link detection isn't possible. It's not too early to ask your equipment vendors if and when they plan to provide support for BFD.
Nortel Networks' VRRP implementation lets both core routers be active, rather than having just one active and the other on standby--plus, Nortel says it will operate in a multivendor environment. Nortel also uses its SMLT (Split Multilink Trunking) protocol so you can deploy 802.3ad between the aggregator and multiple core routers--SMLT tricks the switches into thinking they are connecting to one switch. Nortel says the protocol works across multivendor environments and the company hopes to make it an IETF standard. Hewlett-Packard, meanwhile, uses its mesh technology in its ProCurve switches to balance traffic dynamically across redundant links using flows based on Ethernet addresses. Cisco Systems uses HSRP (Hot Standby Redundancy Protocol), the precursor to VRRP. All these vendors support the standards-based protocols as well.