Ethernet Automatic Protection System
Encyclopedia
Ethernet Automatic Protection Switching (EAPS) is used to create a fault tolerant topology
by configuring a primary and secondary path for each VLAN
.
It was invented by Extreme Networks
. The idea is to provide highly available Ethernet switched rings (commonly used in Metro Ethernet
). Other implementations include Ethernet Protection Switching Ring (EPSR) by Allied Telesis
, "Rapid Ring Protection Protocol"[RRPP] by Huawei/H3C, "ZTE Ethernet Switch Ring" (ZESR) by ZTE.
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 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.
s 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.
Network topology
Network topology is the layout pattern of interconnections of the various elements of a computer or biological network....
by configuring a primary and secondary path for each VLAN
Virtual LAN
A virtual local area network, virtual LAN or VLAN, is a group of hosts with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location...
.
It was invented by Extreme Networks
Extreme Networks
Extreme Networks, founded in 1996, is a publicly listed company that designs, builds, and installs Ethernet network solutions for enterprise and Carrier Class networks.-Corporate History:Extreme Networks is located in Santa Clara, California...
. The idea is to provide highly available Ethernet switched rings (commonly used in Metro Ethernet
Metro Ethernet
A Metro Ethernet is a computer network that covers a metropolitan area and that is based on the Ethernet standard. It is commonly used as a metropolitan access network to connect subscribers and businesses to a larger service network or the Internet...
). Other implementations include Ethernet Protection Switching Ring (EPSR) by Allied Telesis
Allied Telesis
Allied Telesis is a telecommunications company, formerly Allied Telesyn. Headquartered in Japan, their North American headquarters are in San Jose, California...
, "Rapid Ring Protection Protocol"[RRPP] by Huawei/H3C, "ZTE Ethernet Switch Ring" (ZESR) by ZTE.
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 only the primary port on the master node is used to avoid loops (the secondary port is blocked for all non-control traffic).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 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 PDUProtocol data unit
In telecommunications, the term protocol data unit has the following meanings:#Information that is delivered as a unit among peer entities of a network and that may contain control information, address information, or data....
s 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.
Further reading
External links
- RFC 3619 (EAPS)
- ITU-T G.8031/Y.1342 (Dead Link)