Which protocol provides an alternative to the STP, which provides a way to control network loops, handle link failures, and improve convergence time and can coexist with STP?
A. REP
B. Flex links
C. PBB-EVPN
D. IEEE 802.1ah
E. E-TREE
Correct Answer: A
Explanation/Reference:
http://www.cisco.com/c/en/us/support/docs/lan-switching/ethernet/116384-technote-rep-00.html
Why REP?
REP is a protocol used in order to replace the Spanning Tree Protocol (STP) in some specific Layer 2 network designs. The most current STP specification is Multiple Spanning Trees (MST), defined in 802.1Q-2005. Users who want an alternative to MST have these legitimate concerns: STP considers a bridged domain as a whole. As a result, a local failure is recovered if you change the state of an arbitrarily remote link. The apparent unpredictability of STP is only mitigated if you segment the bridged domain in small, independent pieces. Unfortunately, this is complex, if not impossible, to achieve without the removal of some key features from the Spanning Tree (like preventing loops in all scenarios).
STP convergence might seem slow for service providers who expect recovery times of 50 milliseconds (ms), which common in circuit-switching technologies. This slowness is not caused by the protocol itself; the platforms require optimization in order to run STP in a more efficient way. In the meantime, there need to be new solutions that work around platform limitations.
The MST load-balancing configuration is not flexible. In order for MST to achieve instance load-balancing, all the bridges must be part of the same region. Regions are defined by user configuration, and there is no way to modify the MST configuration on a switch without the introducion of some reconvergence in the network. This could be worked around by careful pre-configuration, and to a limited extent, by the use of other protocols such as VLAN Trunk Protocol (VTP) v3.
Explanation/Reference:
http://www.cisco.com/c/en/us/support/docs/lan-switching/ethernet/116384-technote-rep-00.html
Why REP?
REP is a protocol used in order to replace the Spanning Tree Protocol (STP) in some specific Layer 2 network designs. The most current STP specification is Multiple Spanning Trees (MST), defined in 802.1Q-2005. Users who want an alternative to MST have these legitimate concerns: STP considers a bridged domain as a whole. As a result, a local failure is recovered if you change the state of an arbitrarily remote link. The apparent unpredictability of STP is only mitigated if you segment the bridged domain in small, independent pieces. Unfortunately, this is complex, if not impossible, to achieve without the removal of some key features from the Spanning Tree (like preventing loops in all scenarios).
STP convergence might seem slow for service providers who expect recovery times of 50 milliseconds (ms), which common in circuit-switching technologies. This slowness is not caused by the protocol itself; the platforms require optimization in order to run STP in a more efficient way. In the meantime, there need to be new solutions that work around platform limitations.
The MST load-balancing configuration is not flexible. In order for MST to achieve instance load-balancing, all the bridges must be part of the same region. Regions are defined by user configuration, and there is no way to modify the MST configuration on a switch without the introducion of some reconvergence in the network. This could be worked around by careful pre-configuration, and to a limited extent, by the use of other protocols such as VLAN Trunk Protocol (VTP) v3.