Ethernet Automatic Protection Switching (EAPS) is used to create a fault tolerant
topology
In mathematics, topology (from the Greek words , and ) is concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling, and bending; that is, without closing ...
by configuring a primary and secondary path for each
VLAN
A virtual local area network (VLAN) is any broadcast domain that is partitioned and isolated in a computer network at the data link layer ( OSI layer 2).IEEE 802.1Q-2011, ''1.4 VLAN aims and benefits'' In this context, virtual, refers to a ph ...
.
Invented by
Extreme Networks
Extreme Networks is an American networking company based in San Jose, California. Extreme Networks designs, develops, and manufactures wired and wireless network infrastructure equipment and develops the software for network management, policy, a ...
and submitted to IETF as RFC3619. The idea is to provide highly available Ethernet switched rings (commonly used in
Metro Ethernet
A metropolitan-area Ethernet, Ethernet MAN, or metro Ethernet network is a metropolitan area network (MAN) that is based on Ethernet standards. It is commonly used to connect subscribers to a larger service network or the Internet. Businesses c ...
) to replace legacy TDM based transport protection fiber rings. Other implementations include Ethernet Protection Switching Ring (EPSR)
by
Allied Telesis
is a network infrastructure/telecommunications company, formerly Allied Telesyn. Headquartered in Japan, their North American headquarters are in San Jose, California. Founded in 1987, the company is a global provider of secure Ethernet & IP ...
which enhanced EAPS to provide full protected transport of IP Triple Play services (voice, video and internet traffic) for xDSL/FTTx deployments. EAPS/EPSR is the most widely deployed Ethernet protection switching solution deployed with major multi-vendor inter-operability support. The EAPS/EPSR are the basis of the ITU G.8032 Ethernet Protection recommendation.
Operation
A ring is formed by configuring a Domain. Each domain has a single "master node" and many "transit nodes". Each node will have a primary port and a secondary port, both known to be able to send control traffic to the master node. Under normal operation, the secondary port on the master is blocked for all protected vlans.
When there is a link down situation, the devices that detect the failure send a control message to the master, and the master will then unblock the secondary port and instruct the transits to flush their forwarding databases. The next packets sent by the network can then be flooded and learned out of the (now enabled) secondary port without any network disruption.
Fail-over times are demonstrably in the region of 50ms.
The same switch can belong to multiple domains and thus multiple rings. However, these act as independent entities and can be controlled individually.
EAPS v2
EAPSv2 is configured and enabled to avoid the potential of super-loops in environments where multiple EAPS domains share a common link. EAPSv2 works using the concept of a controller and partner mechanism. Shared port status is verified using health
PDUs exchanged by controller and partner. When a shared link goes down, the configured Controller will open only one segment port for each of the protected VLANs, keeping all other segment ports in a blocking state. This state is maintained as long as the Controller fails to receive the health PDUs over the (broken) shared link.
Although not supported by Extreme Networks, it is possible to complete this shared link with non-EAPS (but tag-aware) switches between the Controller and Partner.
When the shared link is restored, the Controller can then unblock its ports, the masters will see their hello packets, and the rings will be protected by their respective masters.
See also
*
Rapid Spanning Tree Protocol
The Spanning Tree Protocol (STP) is a network protocol that builds a loop-free logical topology for Ethernet networks. The basic function of STP is to prevent bridge loops and the broadcast radiation that results from them. Spanning tree also ...
*
Ethernet Ring Protection Switching
Ethernet Ring Protection Switching, or ERPS, is an effort at ITU-T under G.8032 Recommendation to provide sub-50ms protection and recovery switching for Ethernet traffic in a ring topology and at the same time ensuring that there are no loops for ...
References
{{reflist
Further reading
Kwang-Koog Lee, Jeong-dong Ryoo, and Seungwook Min, "An Ethernet Ring Protection Method to Minimize Transient Traffic by Selective FDB Advertisement," ETRI Journal, vol.31, no.5, Oct. 2009, pp.631-633Kwang-Koog Lee, and Jeong-dong Ryoo, "Flush Optimizations to Guarantee Less Transient Traffic in Ethernet Ring Protection," ETRI Journal, vol.32, no.2, Apr. 2010, pp.184-194
External links
* RFC 3619 (EAPS)
ITU-T G.8031/Y.1342
EPSR Feature Overview and Configuration Guide Automatic Protection Switching
Network protocols