MPLS - Resiliency QUESTIONS AND ANSWERS 100%ACCURATE.
What are some methods to provide core network resilience - ✅✅Physical Layer Redundancy
IP Fast Reroute
Loop-Free Alternative
RSVP-TE
LDP
Protocol Redundancy
What are some methods of detecting failures - ✅✅Hello Messages - IGP/RSVP
Bidirectional Forwarding Detection
Ethernet in the First Mile
T/F: IP Fast Reroute works independently of MPLS and thus will not send a PATH Error nor
RESV Tear message to the LSP Head-End - ✅✅False:
What may occur to MPLS traffic when a link is restored - ✅✅MPLS traffic gets discarded
until the receiving router receives a label from the sending router
What is the name of the solution for this error - ✅✅LDP-IGP Synch
Briefly describe how LDP-IGP Synch works - ✅✅The router maintains the LIB & LFIB for a
period of time; this allows it to not discard traffic
What is the difference between a standby and non-standby secondary path - ✅✅Standby path
is signalled immediately after primary path whereas non-standby is only signaled after primary
goes down
Name an advantage and a disadvantage of standby paths - ✅✅Adv - Faster recovery times
Dis - Greater utilization of CPU Resources
What is the difference in the order of standby and non-standby selection criteria; that is to ask:
How would it decide between two standby paths? Two non-standby paths? - ✅✅Two Standby
Paths: Whichever has been up longer
Two Nonstandby Paths: Order of configuration
Alright, here's an order:
Primary, Standby 1, Standby 2
Primary goes up, which gets chosen? - ✅✅Standby 1
Standby 1 goes down which gets chosen? - ✅✅standby 2
, Primary & Standby 1 come back up which gets chosen? - ✅✅Primary
Primary goes down which gets chosen? - ✅✅Standby 2
T/F: A path preference can be defined for both standby and non-standby - ✅✅F: A path
preference cannot be defined for non-standby paths
T/F: The default preference value of a Standby path is 1 - ✅✅F: 255
Which of the following is not an option for Secondary Path Diversity:
Administrative Group
Explicit Hops
Hop-Count
SRLG
None of the Above - ✅✅Hop-Count
How can you maintain path diversity with administrative groups - ✅✅You can color multiple
routers such that even if one route in that general direction goes down, it will just use other
routers in that general direciton
i.e. Upper/Lower
The secondary LSP-paths are automatically _____ from the primary path, if configured for
SRLG - ✅✅disjoint
What is the rule for CSPF in the case of the secondary in the case that the LSP-Paths are
automatically disjoint from the primary? - ✅✅Don't use any of the links that are in the SRLGs
that the primary LSP-Path goes through
T/F: CSPF's primary path is bound by SRLG's - ✅✅F: That would defeat the purpose,
however, any SRLG's it happens to go through are then blocked to secondary paths
What does MPLS Fast Reroute define? - ✅✅Ways of creating backup paths before a failure
What do you think the difference between one to one and facility backup might be? - ✅✅On a
backup path, only one LSP can use it; that is, in a situation in which all LSPs are one to one, for
every backup path, there is a one to one correspondence with an LSP using it
On Facility backup path, a backup path is a facility which is usable by multiple LSPs
In short, sharing is caring is applied by facility whereas one to one are capitalists
What is a one-to-one FRR tunnel called? - ✅✅Detour
What are some methods to provide core network resilience - ✅✅Physical Layer Redundancy
IP Fast Reroute
Loop-Free Alternative
RSVP-TE
LDP
Protocol Redundancy
What are some methods of detecting failures - ✅✅Hello Messages - IGP/RSVP
Bidirectional Forwarding Detection
Ethernet in the First Mile
T/F: IP Fast Reroute works independently of MPLS and thus will not send a PATH Error nor
RESV Tear message to the LSP Head-End - ✅✅False:
What may occur to MPLS traffic when a link is restored - ✅✅MPLS traffic gets discarded
until the receiving router receives a label from the sending router
What is the name of the solution for this error - ✅✅LDP-IGP Synch
Briefly describe how LDP-IGP Synch works - ✅✅The router maintains the LIB & LFIB for a
period of time; this allows it to not discard traffic
What is the difference between a standby and non-standby secondary path - ✅✅Standby path
is signalled immediately after primary path whereas non-standby is only signaled after primary
goes down
Name an advantage and a disadvantage of standby paths - ✅✅Adv - Faster recovery times
Dis - Greater utilization of CPU Resources
What is the difference in the order of standby and non-standby selection criteria; that is to ask:
How would it decide between two standby paths? Two non-standby paths? - ✅✅Two Standby
Paths: Whichever has been up longer
Two Nonstandby Paths: Order of configuration
Alright, here's an order:
Primary, Standby 1, Standby 2
Primary goes up, which gets chosen? - ✅✅Standby 1
Standby 1 goes down which gets chosen? - ✅✅standby 2
, Primary & Standby 1 come back up which gets chosen? - ✅✅Primary
Primary goes down which gets chosen? - ✅✅Standby 2
T/F: A path preference can be defined for both standby and non-standby - ✅✅F: A path
preference cannot be defined for non-standby paths
T/F: The default preference value of a Standby path is 1 - ✅✅F: 255
Which of the following is not an option for Secondary Path Diversity:
Administrative Group
Explicit Hops
Hop-Count
SRLG
None of the Above - ✅✅Hop-Count
How can you maintain path diversity with administrative groups - ✅✅You can color multiple
routers such that even if one route in that general direction goes down, it will just use other
routers in that general direciton
i.e. Upper/Lower
The secondary LSP-paths are automatically _____ from the primary path, if configured for
SRLG - ✅✅disjoint
What is the rule for CSPF in the case of the secondary in the case that the LSP-Paths are
automatically disjoint from the primary? - ✅✅Don't use any of the links that are in the SRLGs
that the primary LSP-Path goes through
T/F: CSPF's primary path is bound by SRLG's - ✅✅F: That would defeat the purpose,
however, any SRLG's it happens to go through are then blocked to secondary paths
What does MPLS Fast Reroute define? - ✅✅Ways of creating backup paths before a failure
What do you think the difference between one to one and facility backup might be? - ✅✅On a
backup path, only one LSP can use it; that is, in a situation in which all LSPs are one to one, for
every backup path, there is a one to one correspondence with an LSP using it
On Facility backup path, a backup path is a facility which is usable by multiple LSPs
In short, sharing is caring is applied by facility whereas one to one are capitalists
What is a one-to-one FRR tunnel called? - ✅✅Detour
