Sso Support For Rep Fast Hello; Rep Edge No-Neighbor Support - Cisco ASR 900 Series Configuration Manual

Configuring Resilient Ethernet Protocol
The figure below shows the delay in failure detection due to hardware limitation of a Copper interface.
Figure 4: Delay in Failure Detection

SSO Support for REP Fast Hello

When a router crashes, it takes between 3 to 5 seconds for the router to get into active mode and start sending
REP Fast Hello packets. If the value of the age out timer configured by the lsl age out timer command is less
than 3 seconds, the remote end detects a port failure and reconverges. After reconverging, the router sends
out a BPDU with a special type, length, and, value (TLV) to the connected port. The router learns the port's
local and remote sequence number so that the subsequent REP three-way link integrity check does not fail.
The Stateful Switchover (SSO) support for REP ensures that a Fast Hello packet can be sent from the router
before the LSL interval expires.

REP Edge No-Neighbor Support

In a ring network topology, aggregation nodes do not support REP. A REP segment can be created with
no-neighbor ports to achieve convergence of switches. The figure below shows P1 and P2 as Edge No-Neighbor
ports in a ring topology. In this configuration P1 and P2 can block traffic. If there is a failure on any of the
links, all the switches with REP configuration converge. Since P1 and P2 are not edges, they do not support
the following tasks:
• Perform VLAN load balancing.
• Detect topology changes to other segments and the Spanning Tree Protocol (STP).
• Choose the port that can preempt.
• Display the complete segment topology.
The Edge No-Neighbor support enables defining a new type of edge that has an internal neighbor. In the figure
below, P1 and P2 are configured as Edge No-Neighbor ports rather than intermediate segment ports. These
ports inherit properties of edge ports and overcome the limitations listed above. Thus, the Edge No-Neighbor
LAN Switching Configuration Guide Cisco IOS XE Everest 16.5.1 (Cisco ASR 900 Series)
SSO Support for REP Fast Hello
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