IP LFA (Loop-Free-Alternate): Architecture and … the MPLS (TE) Overhead = scalability ~50 ms...

IP LFA (Loop-Free-Alternate): Architecture and Troubleshooting

Luc De Ghein – Technical Leader Services

BRKRST-3020

• Introduction

• LFA Overview

• LFA Architecture

• Configuration, implementation and troubleshooting (OSPF, ISIS, EIGRP) on IOS and IOS-XR

• TI-LFA

• MATE

• Conclusion

Agenda

Introduction

Evolution Failure Handling

Routing protocol

computes new best path

– control and data plane* IPv4 is used throughout the presentation –

same principles apply to IPv6

Best effort delivery

Voice/video demanded fast convergence

Fast Rerouting

Service failures caused

by routing transitions are

largely hidden by higher-

level protocols that

retransmit the lost data

Tuned routing

protocol for faster

convergence

Pre-computed

backup/repair path

needed, in data plane

LFA Overview

Goals

Fast RestorationLike MPLS Traffic

Engineering FRR

Without the MPLS

(TE) Overhead =

scalability

~50 ms

Protect link/node

failure

no BW

protection

Simple to

deploy/operate

Incremental

deployment – no

signaling

and local only

Pure IP

MPLS is not a

pre-requisite

LFA and MPLS TE ComparisonIP FRR LFA MPLS TE FRR

Repair Path Least cost Constraints based with bandwidth

guarantee and path control

Link & node protection Yes Yes

Path protection No Yes

Control Plane Requirements None RSVP-TE

Load distribution over multiple

repair paths

Yes No

Provisioning Minimal configuration Significant

IPv6 support Yes No

Shared Risk Link Group (SRLG) Yes (local only) Yes

Network Topology Coverage Effective with mesh

0 % < coverage < 100 %

No dependency. 100 % Coverage.

Always works.

must use MPLS TE

solutions will be

covered

LFA Architecture

Before We Start …

Requirement Building Block

Speed Pre-compute repair path

Speed of restoration Put repair path in data plane (CEF)

Fast Detection Fast Link down detection – best to use BFD*

Cleanup Normal convergence occurs after the event

(*) BFD sessions are only built between the DR and other OSPF routers on a broadcast segment

Reducing Loss Of Connectivity (LoC)Control Plane Fast Convergence

t0 Failure Detection

t1 Failure Propagation (Flooding, Updates, etc)

t2 Topology/Routing Recalculation

t3 Update Routing and Forwarding Table (RIB/FIB)

Data Plane Convergence (FRR)

t0 Failure Detection

tR Switchover to (pre-computed) backup path

t1 Failure Propagation (Flooding, Updates, etc)

t2 Topology/Routing Recalculation

t3 Update Routing and Forwarding Table (RIB/FIB)

failure

LoC

t0

failure

t1 t2 t3 t4

LoC

t0 t1 t2 t3 t4tR

prefix-independent update

Principal Idea Behind LFA

B

A C

primary path

• A does all the computation

• No other router is involved

• Repair path (LFA):

• New link/next-hop router avoind the failed link

• Traffic does not return from B to A

All is done locally on router A

Principal Mechanism of LFANormal Shortest Path Calculation (SPF)

10 10

10 10

30 10

10 10

30

B C

D E F

G H

20

10

A

topology

SPF

SPT

10 10

10 10

30 10

10

B C

D E F

G H

10

G

A

root router

calculating router

&

Principal Mechanism of LFAThe trick = calculating router runs SPF with other router as root

SPF

10 10

10 10

30 10

10 10

30

B C

D E F

G H

20

10

A

topology SPT

10 10

10 10

10

A

B D G

H

10

G

Croot router

calculating router

E

F

30 10

reverse SPF = rSPF

All of the LFA is made possible by the calculating router running an SPF with its neighbor(s) as root

An SPF with any router in the area as root is not needed

Definitions

E

N

DS

primary path

All calculation

occurs here

Source router

Where the prefixes

are connected

Destination router

Alternate next hop

under investigation

Neighbor router

Primary next hop

router

Neighbor routerD(A,B)

The distance (lowest cost) from A to B

primary next hop

alternate next hop

General Theory - Rules

Inequality 1: D(N,D) < D(N,S) + D(S,D)

“Path is loop-free because N’s best path is not through local router.”

Traffic sent to backup next hop is not sent back to S.

Loop Free Alternate

Inequality 2: D(N,D) < D(S,D)

“Neighbor router is closer to the destination than local router.”

Loop-free is guaranteed even with multiple failures (if all repair-paths are

downstream path).

Downstream Path

Inequality 3: D(N,D) < D(N,E) + D(E,D)

“N's path to D must not go through E.”

“The distance from the node N to the prefix via the primary next-hop is

strictly greater than the optimum distance from the node N to the prefix.“

Node protection N

S

E

D

Alternate next hop

under investigation

Primary next hop

router

c

o

v

e

r

a

g

e

General Theory - Rules

Inequality 4: D(N,D) < D(N,PN) + D(PN,D)

“the link from S to N should not be the same as the protected link”

“the link from N to D should not be the same as the protected link”

Loop Free Link Protecting for Broadcast Link

N

S

E

DPN0

0

0

PN = PseudoNode

representing the

BroadCast link with cost 0

General Theory - Examples

10 E

12

5

11

S

N

D

Inequality 3: 11 < 16 + 5 ?

Inequality 2: 11 < 15 ?

Inequality 1: 11 < 12 + 15 ?

Inequality 3: 20 < 22 + 5 ?


Inequality 1: 20 < 12 + 15 ?

Inequality 3: 25 < 20 + 5 ?


Inequality 1: 25 < 12 + 15 ?

Inequality 1 D(N,D) < D(N,S) + D(S,D) Loop Free

Alternate

Inequality 2 D(N,D) < D(S,D) Downstream

path

Inequality 3 D(N,D) < D(N,E) + D(E,D) Node

protection

10 E

12

5

20

S

N

D

10 E

12

5

20S

N

D

General Theory - Examples

Inequality 3: 25 < 20 + 5 ?


Inequality 1: 25 < 20 + 27 ?

Inequality 3: 27 < 22 + 5 ?


Inequality 1: 27 < 12 + 15 ?


Alternate


path


protection

10 E

12

5

27

S

N

D

22 E

20

5

20S

N

D

General TheoryExample 4th Inequality


Alternate


path


protection

N

S

E

DPN

10

0

0

0

10

1011

25

8

Inequality 4 D(N,D) < D(N,PN) + D(PN,D) Loop Free

Alternate BC

Inequality 4: 21 < 10 + 11 ? Loop-free for Broadcast link

21

D(N,D) = 21 and path goes through the PN

“the link from S to N should not be the same as the protected link”

“the link from N to D should not be the same as the protected link”

Per-Link versus Per-Prefix LFA

5

10 N1

10

10

S

N2

E

Per-Link

D1

D2

5

10

10

10

• Backup path carries traffic for all destinations through primary next hop

• There is no difference in path for prefixes to D1 or D2

• Can lead to overloaded links S-N2 and N2-E

• Node protection is possible, but not guaranteed (topology dependent)

• Node protection if path is S-N1-D1, but then suboptimal path for prefixes to D2

D1 + D2

Per-Prefix

5

10 N1

10

10

S

N2

E

D1

D2

5

10

10

10

Two different backup path can carry traffic for different prefixes through primary next hop, and hence produce better load sharing

D2

D1

YY

Per-Link versus Per-Prefix LFA: Coverage

10

10 N

10

15

S

E

D

Per-Link Per-Link

X + Y

E is primary next-hop for prefixes X and Y

Inequality 1 : prefix X : 15 < 10 + 20

Inequality 1 : prefix Y : 20 < 10 + 10

→ No protection for prefix X and Y !

X


Alternate

Conclusion? All or nothing (prefixes) with Per-Link LFA

10

15 N

10

15

S

E

D

X + Y

X

E is primary next-hop for prefixes X and Y

Inequality 1 : prefix X : 15 < 15 + 20

Inequality 1 : prefix Y : 20 < 15 + 10

→ Protection for prefix X and Y !

20 20

Prefixes reachable through the same primary next-hop, share the same backup

Per-Link LFA Limitation

20

16 N1

5

70

S

N2

E

D1

D2

5

40

30

30

Traffic to D2 is forwarded to E on N2

Traffic to D1 is U-turned on N2, back to S

Prefix from D1, NH = S, cost = 51 Prefix from D2, NH = E, cost = 50

20

16 N1

15

70

S

N2

E

D1

D2

5

40

30

30

Prefix from D1, NH = D1, cost = 30Prefix from D2, NH = S, cost = 81

Traffic to D1 is forwarded to D1

Traffic to D2 is U-turned on N1, back to S

Conclusion? Per-Link LFA does not always work

Assume N2 is backup for D1 and D2 prefixes Assume N1 is backup for D1 and D2 prefixes

Per-Link versus Per-Prefix

Per-Link LFA or per-prefix LFA is chosen per interface!

• Simple computation, single rSPF per

protected neighbor

• All or nothing; does not always work

• Low coverage

Per-link

• More complex calculations than per-link LFA, computation is for each neighbor of S and per-prefix

• High coverage

Per-prefix

Calculation & Memory

• Calculation is done in background

• Primary SPF always has priority

SPF

t0 t1 t2 t3tR

IPFRR SPF SPF

IPFRR SPF

IPFRR SPF

t5t4

IPFRR interupted and continued later

t6

• Memory increase: exta information stored• Distance table, backup path in RIB / LRIB / FIB

• But only for the IGP prefixes !

Building Blocks

1. Router S calculates alternate next hop for prefixes/link

2. Alternate next hop is installed in RIB and IGP local RIB (LRIB)

3. Alternate Next hop is installed in FIB (CEF)

Pre-failure

Failure Time

1. Link-down detection

2. Trigger IP-FRR LFA: switchover all prefixes in FIB in one go

Post-failure

1. Normal convergence (SPF)

show ip route 10.1.1.0/24

10.1.1.2 via GE 0/0/1, protected

10.1.2.1 via GE 0/0/2, backup

show ip ospf rib 10.1.1.0/24


10.1.2.1 via GE 0/0/2, repair-path

RIB

LRIB

CEFshow ip cef 10.1.1.0/24


10.1.2.1 via GE 0/0/2, repair-path

10 E

12

5

11

S

N

D

show ip cef 10.1.1.0/24

10.1.2.1 via GE 0/0/2

show ip cef 10.1.1.0/24

10.1.2.1 via GE 0/0/2

CEF

CEF

stored in control plane

stored in data plane

• Does LFA work with Labelled traffic?

• Yes!

• Least cost routing with LDP

• LDP requirement: Downstream Unsolicited; Liberal Retention

• No issue (except for ATM interfaces)

• Different label for different prefix

• LFIB must store backup path

• Services are L3VPN, VPLS, 6PE/6VPE

LFA and MPLS

MPLS Primary path

LFA

Using MPLS to Increase LFA Coverage

The problem

• Remote LFA: tunnel the packets to a router which can deliver the packets without going across the failed link - guaranteed

The solution

• Directly Connected LFA* does not cover all• No neighbor is found which is an LFA

• Typically

• A network with range of link metrics

• A sparsely meshed network

• A ring topology

S

R4

R2

R3

D

R5

1

1 1

1

11

Drop-off router

*Everything seen so far

Finding the Drop-off Router

S E

P space of Router S Q space of Router E

P-space of S and the link SE =

set of routers that S can reach

without passing through the

link SE (including ECMP)

Q-space of the E and the link

SE = set of routers that can

reach the router E without

passing through the link SE

PQ

PQ

PQ

P QPQ

Common router P & Q

S picks one PQ router (closest)

S builds tunnel to PQ router (if not already present)

Extended P-Space

• What if no PQ router is found?

EP QExtended P space of Router S

Extended P-space of S and the link

SE = set of routers that all neighbors

of S can reach without passing

through the link SE (including ECMP) PQ

PQ

S

N

… more coverage

… extended P-Space turned on if remote LFA is turned on

Remote LFACalculating P-Space

A

B

D

C

E

SPF

topology

A

B

D

C

E

SPT

A

B

D

SPT after pruning protected link branch

pruning

Compute SPT in protecting router Prune branch through the protected

link (including ECMP)

P

Remote LFACalculating Q-Space

A

B

D

C

E

rSPF

topology

A

B

D

C

E

rSPT rooted at C

pruning

SPT after pruning protected link branch

D

C

E

Compute rSPF rooted on link far

end router

Prune branch through the protected

link (including ECMP)

Q

Remote LFACalculating the Set of PQ Candidates

P Q∩

D E

B

D∩

A

B

D

C

E

topology

PQ candidate

Extended P-Space calculation is not

expensive; the router already runs SPF in

behalf of every neighbor with Directly

Connected LFA

Remote LFAPacket Forwarding

A

B

D

C

E

PQ router

X

1Find PQ

router

2Targeted LDP

Session

3Label Binding

Exchange

LDP Label Binding

Prefix X

Label 99

IP 17

IP30

IP

Topologies

A

C

B

D

square

pentagon … to ring

triangle B

C

A

If link cost range is small …

… very high LFA coverage

If equal link cost:

No LFA

No Remote LFA

Remote LFA with Extended P-Space

A

B

D

C

E

A

B

C

D

E

N No LFA

Remote LFA

Microloops• Link failure S-D

• T0 link failure detected

• tR IP-FRR kicks in on S

• t1 Failure Propagation (Flooding, Updates, etc)

• t2 Topology/Routing Recalculation (SPF runs on S)

• t3-t4 Update Routing and Forwarding Table (RIB/FIB)

• t4 end of updating on S

• t5 end of updating on N

• [t3-t4]-[t4-t5] N still has route for D, pointing to S: loop

• t5 loop resolved: N finished updating its tables: then route for D points to R1

LoC

t0 t1 t2 t3 t4tRfailure t5

loop

N R1 R2

S D

rLFA tunnel

The solution is to delay updating the

forwarding table

Until all routers converged. In the meantime, traffic remains on rLFA protected path

Configuration, implementation and troubleshooting (OSPF, ISIS,

EIGRP) in IOS and IOS-XR

• There can be multiple possible backup path

• Only one is chosen to protect the primary path

• Which one to choose?

Tie-Breaking

attribute order configurable

• A characteristic of a path• Each path can have any

combination of attributes

• Elimination rules• Importance/preference of

attributes

• Any combination of attributes can be configured

• Order can be changed• There is a default set• Configure any attribute

removes all the default oneSRLG, node protecting,

downstream, primary/secondary, …If one rule eliminates all paths: skip

the rule

Tie-Breaking Attributes

SRLG Prefer other Share Link Group

Primary Path Prefer Primary over Secondary path

Interface Disjoin Prefer other interface then protected interface

Node protecting Prefer node over link protecting

Broadcast Interface Disjoin Prefer Path not using the broadcast segment

Load Sharing Distribute candidates among prefixes sharing the protected path

Downstream Prefer the router closer to D than S

Secondary Prefer scondary over primary

Tie-Breaking Example (OSPF)R1#show ip ospf rib 10.100.1.13

via 10.1.5.7, Ethernet0/0

repair path via 10.1.3.4, Serial4/0, cost 31

Flags: RIB, Repair, , BcastDj, , LC Dj, NodeProt, Downstr, LoadShare


Flags: , Repair, IntfDj, BcastDj, LC Dj


Flags: , Repair, , BcastDj, , LC Dj, NodeProt, Downstr, LoadShare

repair path via 10.1.5.6, Ethernet0/0, cost 31

Flags: , Repair, , NodeProt, Downstr


Flags: , Repair, IntfDj, BcastDj, LC Dj, NodeProt

PrimPath

PrimPath

PrimPath

Ignore

Ignore

Ignore

Ignore

IntfDj

IntfDj

primary path Default Tie Breaking, IOS, OSPF

1

2

3

4

5

10 srlg

20 primary-path

30 interface-disjoint

40 lowest-metric

50 linecard-disjoint

60 node-protecting

70 broadcast-interface-disjoint

256 load-sharing

no path has SRLG, so this policy step is skipped

path 2 & 5 do not have “PrimPath” (not one of the

ECMP paths)

path 4 does not have “IntfDj” attribute

paths 1 & 3 have the same cost

paths 1 & 3 have the same set of attributes

it comes down to “loadshare” : one of the 2

paths is chosen

repair path

• LDP must be enabled everywhere

• Enable Targeted LDP everywhere

• No other tunneling mechanisms other than MPLS are supported

• PQ node is link protecting only, not node protecting

• PQ node calculations are only executed if there are unprotected paths for protectable prefixes

• A targeted LDP session to PQ node will only be built if none exists yet

• No Remote LFA for per-link

Remote LFA

e.g. mpls ldp discovery targeted-hello accept [from <acl>]

Implementation Notes

IOS-XR IOS

OSPF

ISIS

Per-Link LFA

Per-Prefix LFA

IPv6

Remote LFA

EIGRP

Inter-area/AS LFA - OSPF

B

C

A

D

E

F

G

H

I

• Router is in one area: intra-area prefixes and all others types are protected

• On the ABR: No prefixes protected from area’s where LFA is not enabled

• Backup path for the prefix will always be calculated in the same area where primary path exists (so not necessarily the shortest path, intra-area is preferred over inter-area and so on)

• Backup path will be of same route type (intra-area, inter-area, external, external-NSSA) and using same metric type (external, NSSA) as primary path

• To protect externals you MUST have enabled the command without the area keyword

• Even if the router is only inside one area! (for example the complete router is area 3 only)

area 1 area 2area 0

• The generated default route (ATT-bit) in L1 is protected in IOS-XR

• For IOS: Enhancement

• Backup path for the prefix will always be calculated in the same level where primary path exists

• Backup path will be of same route type as primary path

• L1 protected by L1

• L2 protected by L2

• L1 will not be protected by L2 prefix

• Externals are protected in L1 or L2

• Inter-area routes (leaked routes L2 into L1) can be protected

Inter-level/AS LFA - ISIS

B

C

A

D

E

F

G

H

I

Level 1 Level 1

Level 2

• Enable fast-reroute per-prefix per area or globally

Configuration - OSPF

• Enable fast-reroute prefix-priority

• Change priority of prefixes (route-map | RPL)

• Change/add/delete tie-breakers; change preference

mandatory

optional

• Exclude an interface for protection

• Exclude an interface for repair path

• Enable Remote LFA

Default: /32 is high in IOS

/32 is medium in IOS-XR

*IOS-XR also has per-link LFA

• Configure a max cost for Remote LFA tunnel

• Enable fast-reroute per-prefix per level or globally

Configuration - ISIS

mandatory

optional

• Enable fast-reroute prefix-priority

• Change priority of prefixes (route-map | RPL)

• Change/add/delete tie-breakers; change preference

• Exclude an interface for protection

• Exclude an interface for repair path

• Enable Remote LFA

Default: /32 is high in IOS

/32 is medium in IOS-XR

• Configure a max cost for Remote LFA tunnel

*IOS-XR also has per-link LFA

Configuration

OSPF – IOS - Configuration• Configuration for ISIS and IOS-XR implementations: see Appendix

[no] fast-reroute per-prefix enable [area <area-id>] prefix-priority {high | low}

• External routes do not belong to any area

• To protect externals you MUST have enabled the command without the area keyword

• High priority get programmed before low priority in RIB

• Default high priority: /32 prefixes

• Enabling ‘low’ priority means that both high and low priority prefixes are eligible for protection

OSPF router config mode

[no] prefix-priority high route-map <route-map>

• Routes permitted by the route-map are assigned high priority, the

rest is low priority

Route-map match statements:match tag

match route-type

match ip address

Other ‘match’ and all ‘set’ statements are ignored

OSPF – IOS - Configuration

[no] fast-reroute per-prefix tie-break <attribute> [required] index <priority>


• Keyword ‘required’ is supported for all

attributes except ‘lowest-metric’

• If required attribute is missing, skip the

path

[no] fast-reroute keep-all-paths

• Keeps all candidate repair-paths in LRIB (for troubleshooting only)

• By default: only best repair path in RIB (conserves memory)

supported attributes

interface-disjoint broadcast-interface-disjoint srlg downstream

node-protecting linecard-disjoint primary-path secondary-path lowest-metric

OSPF – IOS - Configuration

Interface config mode

[no] ip ospf fast-reroute per-prefix protection [disable]

• Primary routes pointing to this interface will not be protected

[no] ip ospf fast-reroute per-prefix candidate [disable]

• The interface will not be used for repair paths

• LFA SPF optimization:

• If interface cannot be used for repair paths then it is not needed to

run SPF with neighbors over this interface as root.

• For example: link from a router to stub site

• Reduced number of SPF: brings total LFA FRR SPF time down

OSPF IOS - Configuration


[no] fast-reroute per-prefix remote-lfa [area area-id] tunnel mpls-ldp

[no] fast-reroute per-prefix remote-lfa [area area-id] maximum-cost distance

• Enable remote LFA globally or per area

• Only MPLS tunneling is supported

• If not configured, Directly Connected LFA can be active

• Configure a maximum cost for the LFA tunnel

Default Tie Breaking OSPF - IOS

Tie-Breaker option Description Default Values Comment

srlg (SRLG) Prefer LFA not sharing the same Share Link Group 10 Shared risk of links

primary-path (PrimPath) Prefer primary over secondary path 20 Backup is member of ECMP set

interface-disjoint (IntfDj) Prefer path over other interface than protected one 30

lowest-metric (CostWon) Prefer lower metric 40 The metric of the backup node to D

might be higher than metric of S to D

linecard-disjoint (LC Dj) Prefer path using different linecard 50 Different linecard means also

different interface, hence this is also

link protecting

node-protecting (NodeProt) Prefer node protecting over link protecting 60

broadcast-interface-disjoint

(BcastDj)

Prefer path not using broadcast segment 70

load-sharing (LoadShare) Distribute remaining candidates among prefixes

sharing the protected path

255 Not configurable.

This is the catch-at-the-end policy

downstream (Downstr) Prefer node closer to D than S - Disabled by default

secondary-path Prefer secondary over primary path - Disabled by default

OSPF IOS – Configuration - Exampleinterface Ethernet1/0

srlg gid 100

ip address 10.1.1.4 255.255.255.0

mpls ip

!

interface Ethernet2/0

ip address 10.1.2.4 255.255.255.0

ip ospf fast-reroute per-prefix protection disable

mpls ip

!


srlg gid 100

ip address 10.1.2.4 255.255.255.0

!


srlg gid 200

ip address 10.1.8.4 255.255.255.0

ip ospf fast-reroute per-prefix candidate disable

!

router ospf 1

prefix-priority high route-map lfa-ospf

fast-reroute per-prefix enable prefix-priority high

fast-reroute per-prefix remote-lfa tunnel mpls-ldp

fast-reroute per-prefix remote-lfa maximum-cost 1000

fast-reroute per-prefix tie-break srlg index 10

fast-reroute per-prefix tie-break node-protecting index 20

fast-reroute keep-all-paths

network 10.1.0.0 0.0.255.255 area 0

!

ip prefix-list lfa-high seq 5 permit 10.0.0.0/8 ge 30

!

route-map lfa-ospf permit 10

match ip address prefix-list lfa-high

SRLG on interface

Enables LFA for high prefixes

Defines high prefixes with route-map

Tie break first SRLG, then

node-protecting, nothing else

Keep all repair paths in control

plane, not only the best one

No prefix with this interface

as next-hop gets protection

The interface will not be

used for repair paths

Enables remote-lfa

Max distance for PQ router is

1000

ISIS IOS – Configuration - Exampleinterface Ethernet5/0

ip address 10.1.7.4 255.255.255.0

ip router isis 1

mpls ip

isis network point-to-point

isis fast-reroute protection level-1 disable

!


ip address 10.1.8.4 255.255.255.0

ip router isis 1


isis fast-reroute candidate level-1 disable

!


ip address 10.1.5.4 255.255.255.0

ip router isis 1


isis fast-reroute exclude level-1 Ethernet5/0

!

router isis 1

net 49.0001.0000.0000.0001.00

is-type level-1

metric-style wide level-1

fast-reroute per-prefix level-1 route-map isis-lfa

fast-reroute tie-break level-1 downstream 10

fast-reroute tie-break level-1 node-protecting 20

fast-reroute remote-lfa level-1 mpls-ldp maximum-metric 1000

!

ip prefix-list loopbacks-level-1 seq 10 permit 10.100.1.0/25 ge 32

!

route-map isis-lfa permit 10

match ip address prefix-list loopbacks-level-1

No prefix with this interface

as next-hop gets protection

The interface will not be

used for repair paths

Interface Eth5/0 cannot be

repair-path for interface Eth7/0

Tie break first downstream, then

node-protecting, nothing else

Protect only primary /32 prefixes

Max distance for PQ router is

1000

Troubleshooting

VerifyingR1#show ip ospf fast-reroute

OSPF Router with ID (10.100.1.4) (Process ID 1)

Loop-free Fast Reroute protected prefixes:

Area Topology name Priority Remote LFA Enabled

0 Base High No

AS external Base High

Repair path selection policy tiebreaks:

10 srlg

20 node-protecting

256 load-sharing

OSPF/RIB notifications:

Topology Base: Notification Disabled, Callback Not Registered

Last SPF calculation started 00:02:50 ago and was running for 3 ms.

priority low would indicate that high

and low priority prefixes are protected

Checking the Coverage

R1#show ip ospf fast-reroute prefix-summary

Area 0:

Interface Protected Primary paths Protected paths Percent protected

All High Low All High Low All High Low

Se6/0 Yes 5 2 3 2 2 0 40% 100% 0%

Se5/0 Yes 8 5 3 2 2 0 25% 40% 0%

Se3/0 Yes 0 0 0 0 0 0 0% 0% 0%

Se2/0 Yes 3 2 1 2 2 0 66% 100% 0%

Et0/0 Yes 11 6 5 3 3 0 27% 50% 0%

Area total: 37 21 16 13 13 0 35% 61% 0%

Process total: 37 21 16 13 13 0 35% 61% 0

Coverage in percentage

Per area

Per interface

High - low

# paths: counted as prefixes with unique path

so a prefix with 2 next hops in the RIB is counted as 2 paths

Verifying Repair-PathsP1#show ip route repair-paths

...

O 10.100.1.3/32 [110/11] via 10.1.3.3, 01:42:28, Ethernet3/0

Repair Path: 10.1.7.8, via Ethernet5/0

[RPR][110/21] via 10.1.7.8, 01:42:28, Ethernet5/0

P1#show ip route 10.100.1.3

Routing entry for 10.100.1.3/32

Known via "ospf 1", distance 110, metric 11, type intra area

Last update from 10.1.3.3 on Ethernet3/0, 01:47:36 ago

Routing Descriptor Blocks:

* 10.1.3.3, from 10.100.1.3, 01:47:36 ago, via Ethernet3/0

Route metric is 11, traffic share count is 1

Repair Path: 10.1.7.8, via Ethernet5/0P1#show ip ospf rib 10.100.1.3

OSPF Router with ID (10.100.1.4) (Process ID 1)

OSPF local RIB

Codes: * - Best, > - Installed in global RIB

LSA: type/LSID/originator

*> 10.100.1.3/32, Intra, cost 11, area 0

SPF Instance 52, age 03:21:53

Flags: RIB, HiPrio

via 10.1.3.3, Ethernet3/0

Flags: RIB

LSA: 1/10.100.1.3/10.100.1.3

repair path via 10.1.7.8, Ethernet5/0, cost 21

Flags: RIB, Repair, IntfDj, BcastDj, LC Dj

LSA: 1/10.100.1.3/10.100.1.3P1#show ip cef 10.100.1.3/32

10.100.1.3/32

nexthop 10.1.3.3 Ethernet3/0 label [implicit-null|17]

repair: attached-nexthop 10.1.7.8 Ethernet5/0

RIB

LRIB

FIB (CEF)

Troubleshooting – Remote LFA

Verify repair Verify PQ routerVerify targeted LDP session

Verify MPLS labels

R1#sh ip route 10.100.1.5



Last update from 10.1.4.5 on Serial5/0, 01:38:12 ago


* 10.1.4.5, from 10.100.1.5, 01:38:12 ago, via Serial5/0


Repair Path: 10.100.1.11, via MPLS-Remote-Lfa4



Verify MPLS labels

R1#show ip ospf rib 10.100.1.5

*> 10.100.1.5/32, Intra, cost 11, area 0

SPF Instance 81, age 1d17h

Flags: RIB, HiPrio

via 10.1.4.5, Serial5/0

Flags: RIB

LSA: 1/10.100.1.5/10.100.1.5

repair path via 10.100.1.11, MPLS-Remote-Lfa4, cost 31

Flags: RIB, Repair, IntfDj, BcastDj, LC Dj, LoadShare

LSA: 1/10.100.1.5/10.100.1.5

R1#show ip interface brief

Interface IP-Address OK? Method Status Protocol

MPLS-Remote-Lfa4 10.1.5.1 YES unset up up

MPLS-Remote-Lfa5 10.1.4.1 YES unset up up

PQ router



Verify MPLS labels

R1#show ip ospf fast-reroute remote-lfa tunnels

Interface MPLS-Remote-Lfa4

Tunnel type: MPLS-LDP

Tailend router ID: 10.100.1.11

Termination IP address: 10.100.1.11

Outgoing interface: Ethernet0/0

First hop gateway: 10.1.5.6

Tunnel metric: 21

Protects:

10.1.4.5 Serial5/0, total metric 31

...

PQ router

What primary next-hops are

protected? (could be more

than one)



Verify MPLS labels

R1#sh mpls ldp neighbor 10.100.1.11

Peer LDP Ident: 10.100.1.11:0; Local LDP Ident 10.100.1.1:0

TCP connection: 10.100.1.11.43185 - 10.100.1.1.646

State: Oper; Msgs sent/rcvd: 72/72; Downstream

Up time: 00:28:54

LDP discovery sources:

Targeted Hello 10.100.1.1 -> 10.100.1.11, active

Addresses bound to peer LDP Ident:

10.1.13.11 10.1.18.11 10.1.14.11 10.100.1.11

R1#sh mpls ldp discovery

Discovery Sources:

Interfaces:

Ethernet0/0 (ldp): xmit/recv

LDP Id: 10.100.1.6:0

Targeted Hellos:

10.100.1.1 -> 10.100.1.11 (ldp): active, xmit/recv

LDP Id: 10.100.1.11:0

The Targeted LDP Session could be set up either by configuration or the FRRManager



Verify MPLS labels

R1#show ip cef 10.100.1.5 detail

10.100.1.5/32, epoch 0

local label info: global/33

nexthop 10.1.4.5 Serial5/0 label [implicit-null|37]

repair: attached-nexthop 10.100.1.11 MPLS-Remote-Lfa4

nexthop 10.100.1.11 MPLS-Remote-Lfa4, repair

R1#show mpls ldp bindings 10.100.1.5 32

lib entry: 10.100.1.5/32, rev 50

local binding: label: 33

remote binding: lsr: 10.100.1.2:0, label: 37

remote binding: lsr: 10.100.1.4:0, label: 36

remote binding: lsr: 10.100.1.5:0, label: imp-null

remote binding: lsr: 10.100.1.11:0, label: 37remote LFA label received from the PQ node over

the targetted session

remote LFA label

primary label

Troubleshooting - Debugging

R1#debug ip ospf fast-reroute rib ?

<1-199> Access list

<1300-2699> Access list (expanded range)

<cr>

See next two slidesR1#debug ip ospf fast-reroute spf ?

detail Print more debugging detail

<cr>


OSPF-1 INTRA: Running SPF for area 0, SPF-type Full

A major change in the network causes OSPF to run a full SPF and FRSPF

OSPF-1 FRSPF: Scheduling IPFRR SPF, change 'X', area dummy area, instance 440

...

OSPF-1 FRSPF: Create list of candidate neighbors for intra SPF in area 0

OSPF-1 FRSPF: Adding neighbor 10.100.1.8 via Serial6/0 to SPF work queue

OSPF-1 FRSPF: Adding neighbor 10.100.1.7 via Ethernet0/0 to SPF work queue

...

OSPF-1 FRSPF: Intra-area calcualtion for neighbor 10.100.1.7 in area 0

Normal full SPF

Adding router LSAs and building SPT

Adding summaries, externals, etc.

Start of FRSPF

The neighbors of the

calculating router for which

rSPF will be run

rSPF for one neighbor

RmtLFA is enabled: extended

P-space is built as well

P legs are stored in the remote

LFA tree

OSPF-1 FRSPF: Add router 10.100.1.7 to P-space via neighbor 10.100.1.7

OSPF-1 FRSPF: Adding first hop via 10.1.5.7 Ethernet0/0

...


OSPF-1 FRSPF: Need RmtLFA tunnel for primary gateway 10.1.1.2 Serial2/0 in area 0 due to unprotected 10.1.7.0/24

...

OSPF-1 FRSPF: RmtLFA starting rSPF in area 0

OSPF-1 FRSPF: Found router 10.100.1.11 in Q-space of gateway 10.1.5.6 Eth0/0

OSPF-1 FRSPF: protecting via 10.1.4.5 Serial5/0 with tunnel/total cost

20/30, flags (Repair, IntfDj, BcastDj, SRLG, LC Dj)

OSPF-1 FRSPF: currently best known tunnel

%LDP-5-NBRCHG: LDP Neighbor 10.100.1.13:0 (3) is UP

OSPF-1 FRSPF: Place tunnels in area 0

OSPF-1 FRSPF: Starting RmtLFA scan

OSPF-1 FRSPF: Intra-area reverse SPF calcualtion for neighbor 10.100.1.6 in area 0

Start RmtLFA scan

Neighbors for which there is at least one

unprotected prefix: remote LFA will be

checked (but not necessarily found) for

these neighbors

Start rSPF for RmtLFA

Run rSPF for each of the next-hops,

with the next-hop as root

Found Q leg

Trying to match P legs and Q

legs, resulting in PQ nodes

Tunnels are placed to PQ nodes

One or more Targetted LDP neighbors come up

OSPF – Per Neighbor Table

D(N,D) < D(N,E) + D(E,D)

D(N,D) equals D(S,D)viaN - D(S,N)

D(S,D)viaN - D(S,N) < D (N,E) + D(S,D) - D(S,E)

D(N,E) + D(E,D) equals D (N,E) + D(S,D) - D(S,E)

S

E is the primary

next hop router

N is the protecting

next hop router

E

N

D

Base LFA condition

Distance from N to D is not needed and hence D(N,D) is not stored– The distance from a neighbor to all other routers is not needed– The same applies to D(E,D)

Some info needs to be stored in new tables to be used by partial SPF in between full SPFs: per-neighbor table

Stored in LRIB (primary path)

Stored in LRIB (repair path)

Stored in per neighbor table

D(S,N) & D(S,E) stored internally

Per-Neighbor TableExample for one neighbor

R1# show ip os neighbor fast-reroute | begin ID 10.100.1.2

Neighbor with Router ID 10.100.1.2:

Reachable over:

Serial2/0, IP address 10.1.1.2, cost 10

Router distance table:

10.100.1.1 i [10]

10.100.1.2 i [0]

10.100.1.3 i [10]

10.100.1.9 i [25]

10.100.1.10 i [30]

10.100.1.13 i [40]

Network LSA distance table:

10.1.5.7 i [20]

External LSA forwarding address distance table:

10.200.1.2 i [50] via 10.200.1.0/24

neighbor N of S

(root of SPF)

D(S,N)

neighbors E of S

with D(N,E)

ABRs/ASBRs with

D(N,ABR/ASBR)

D(N,PN)

cost from N to DR

equivalent info as “show …” command on router with ID 10.100.1.2

R2#show ip ospf border-routers

i 10.100.1.9 [25] via 10.1.1.1, Serial2/0, ASBR, Area 0, SPF 25

i 10.100.1.10 [30] via 10.1.7.3, Serial3/0, ABR, Area 0, SPF 25

i 10.100.1.13 [40] via 10.1.1.1, Serial2/0, ABR/ASBR, Area 0, SPF 25

R2# show ip route 10.200.1.2



Last update from 10.1.1.1 on Serial2/0, 2d23h ago


* 10.1.1.1, from 10.100.1.13, 2d23h ago, via Serial2/0


R2#show ip ospf database network

LS Type: Network Links

Link State ID: 10.1.5.7 (address of Designated Router)

Advertising Router: 10.100.1.7

Length: 36

Network Mask: /24

Attached Router: 10.100.1.7

i intra-area route

I inter-area route

N

S

(R2)

To Forwarding Address

IOS-XRRP/0/RP1/CPU0:MeltDown#show route

Codes: C - connected, S - static, R - RIP, B - BGP, (>) - Diversion path

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - ISIS, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, su - IS-IS summary null, * - candidate default

U - per-user static route, o - ODR, L - local, G - DAGR

A - access/subscriber, a - Application route, (!) - FRR Backup path

Gateway of last resort is 10.48.32.1 to network 0.0.0.0

O E2 1.1.1.1/32 [110/0] via 10.1.2.7, 00:08:34, GigabitEthernet0/0/4/0 (!)

[110/20] via 10.1.11.3, 00:08:34, GigabitEthernet0/0/4/3

O 10.1.8.0/24 [110/2] via 10.1.7.4, 00:31:10, GigabitEthernet0/0/4/2

O 10.1.9.0/24 [110/3] via 10.1.7.4, 00:08:34, GigabitEthernet0/0/4/2

[110/0] via 10.1.11.3, 00:08:34, GigabitEthernet0/0/4/3 (!)

Troubleshooting OSPF - IOS-XRRP/0/RP1/CPU0:MeltDown#show ospf

…

IPFRR per-prefix tiebreakers:

Name Index

No Tunnel (Implicit) 255

Node Protection 40

Line-card Disjoint 30

Lowest Metric 20

Primary Path 10

Downstream 0

Secondary Path 0

SRLG Disjoint 0

…

Area BACKBONE(0)

Number of interfaces in this area is 4

SPF algorithm executed 24 times

Number of LSA 12. Checksum Sum 0x045507

…

Flood list length 0

Number of LFA enabled interfaces 3, LFA revision 29

Number of Per Prefix LFA enabled interfaces 3

Number of neighbors forming in staggered mode 0, 2 full

Default or configured tie breakers

Troubleshooting OSPF - IOS-XR

RP/0/RP1/CPU0:MeltDown#show ospf routes 10.1.100.6/32 backup-path

Codes: O - Intra area, O IA - Inter area

O E1 - External type 1, O E2 - External type 2

O N1 - NSSA external type 1, O N2 - NSSA external type 2

O 10.1.100.6/32, metric 3 area 0.0.0.0

10.1.7.4, from 10.1.100.7, via GigabitEthernet0/0/4/2, path-id 1

Backup path:

10.1.1.7, from 10.1.100.7, via GigabitEthernet0/0/4/1, protected bitmap 0x1

Attribues: Metric: 2, Downstream, Node Protect, SRLG Disjoint

RP/0/RP1/CPU0:MeltDown#show ospf statistics fast-reroute

ospf_show_stats_ipfrr

OSPF 1 IPFRR Statistics:

Number of paths: 16

Number of paths enabled for protection : 16 (100%)

Number of paths protected: 13 (81%)

Troubleshooting Roundup• LFA coverage might not be 100%

• LFA is default only for /32 prefixes

• LFA enabled for external prefixes?

• Potential Remote LFA issues

• LDP targeted session enabled?

• Enable “fast-reroute keep-all-paths” in IOS in order to easily compare the path attributes

• Use show commands (IOS or IOS-XR equivalent commands)• show ip route <prefix>

• show ip route repair <prefix>

• show ip ospf rib <prefix>

• show ip cef <prefix>

• Use debug commands

EIGRP

EIGRP - LFA

• Only Per-Prefix LFA

• EIGRP uses the Diffusing Update Algorithm (DUAL) to calculate the successor and feasible successors

• Uses existing Feasible Successors for repair paths, so no additional computational load

• New: repair route is ready in the data plane

• Automatically enabled on all interfaces covered by the protocol

• Repair paths can be equal or unequal cost (though variance command)

Feasible Successor

256*

min

107

delays

bandwidthmetric

router#show ip eigrp topology 10.1.100.1 255.255.255.255

EIGRP-IPv4 VR(one) Topology Entry for AS(1)/ID(10.1.100.3) for 10.1.100.1/32

State is Passive, Query origin flag is 1, 1 Successor(s), FD is 1376256, RIB is 10752

Descriptor Blocks:

10.1.11.1 (GigabitEthernet1/10), from 10.1.11.1, Send flag is 0x0

Composite metric is (1376256/131072), route is Internal

Vector metric:

Minimum bandwidth is 1000000 Kbit

Total delay is 11000000 picoseconds

Reliability is 255/255

Load is 1/255

Minimum MTU is 1500

Hop count is 1

Originating router is 10.1.100.1

10.1.5.7 (GigabitEthernet1/4), from 10.1.5.7, Send flag is 0x0

Composite metric is (1376583/131399), route is Internal

Vector metric:

Minimum bandwidth is 1000000 Kbit

Total delay is 11005000 picoseconds

Reliability is 255/255

Load is 1/255

Minimum MTU is 1000

Hop count is 2

Originating router is 10.1.100.1

Feasibility Condition (loopfree) = Reported Distance (RD) by neighbor is lower than Feasible Distance (FD)

Feasible Distance (FD)

Reported Distance (RD)

Successor

Feasible Successor

RD < FD

131399 (RD) < 137625 (FD)

Repair Path

IP-FRR LFA enabled?

EIGRP - LFA

• Coverage is not necessarily 100%

• Design the network to have Feasible Successors

E1

N

S

E2

E4

E3

D

100100

Successor

FD = 200

300 150

190

210

300

200

50

50

Feasible Successors

Non-Feasible Successors

Primary Path

Potential Repair Paths

Configuration & Troubleshootingrouter eigrp one

!

address-family ipv4 unicast autonomous-system 1

!

topology base

fast-reroute per-prefix all

exit-af-topology

network 10.0.0.0

router#show ip eigrp topology frr

P 10.1.100.1/32, 1 successors, FD is 1376256

via 10.1.11.1 (1376256/131072), GigabitEthernet1/10

via 10.1.5.7 (1376583/131399), GigabitEthernet1/4, [LFA]

• [no] fast-reroute load-sharing disable

• [no] fast-reroute per-prefix {all|route-map}

• [no] fast-reroute per-prefix tiebreak {lowest-backup-path-metric | interface-disjoint | linecard-disjoint | srlg-disjoint} <priority number>

• debug eigrp frr

• show ip eigrp topology frr

TI-LFA

• Leverages Segment Routing (SR)

• Can provide 100% coverage

• What is Segment Routing?

• Source routing – ordered list of segments

• Stack of MPLS labels

• IPv6 Routing Extension

• MPLS labels are advertised by the IGP

• Simplicity

• TI-LFA = SR + LFA

• TI-LFA provides Link and Node Protection

• TI-LFA uses P/Q nodes

Topology Independent (TI) LFA

A B C D

E F G H

I

319

1900

2000

319

1900

2000

319

1900

319

segment 1segment 2

segment 3

319

TI-LFA IOS-XR Example

P Q

A

B

C

D

G

F

E

1

1

1

10

1

1

segment 1

segment 3

segment 2319

1900

319319

1900

2000

• Calculate P and Q space

• Calculate post-convergence path

• Find P and (adjacent) Q router

• P and Q can be different router!

• Almost full coverage with 2 segments (~99%)

• Prefer less segments

• Fallback to remote LFA if TI-LFA finds no repair paths

• Enabled by configuration

• Prefer least amount of segments

• Node protection preferred over link protection

• Less tie-breakers

• load-share, lowest-backup-metric, lc-disjoint and srlg-disjoint

• Use post-convergence path

• Less convergence

• No need for targeted LDP session

TI-LFA IOS-XRrouter ospf 1

router-id 10.100.1.2

fast-reroute per-prefix ti-lfa enable

MATE

• Modeling, simulating, forecasting, planning, optimization, analysis of complex networks

• Offline and online

• Network discovery

• IGP, BGP, MPLS TE, QOS, Layer, VPN, and multicast

• IPFRR-LFA Add-on

• TI-LFA Add-on

MATE

Technote on MATE IPFRR LFA Add-on

http://www.cisco.com/c/en/us/support/docs/routers/mate-design/118769-technote-ipfrr-00.html

http://www.cisco.com/c/en/us/support/docs/routers/mate-design/118769-technote-ipfrr-00.html

IPFRR LFA Add-on

IPFRR LFA Coverage/PQ Node

100% coverage

0% coverage0% < coverage < 100%

Conclusion

Conclusion

TI-LFA

Remote LFA

Direct LFA

Topology coverage

ring

square

little

meshed

extreme link

metrics

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Thank you

Appendix

Configuration IOS-XR - OSPFCommand Router / Interface Comment

fast-reroute per-prefix router/interface

fast-reroute per-link router/interface

fast-reroute per-prefix exclude interface {interface-name} interface

fast-reroute per-prefix lfa-candidate interface {interface-name}

interface used for allowing TE tunnel (explicit-path)

other interface types are by default on the lfa-candidate list

fast-reroute per-prefix use-candidate-only interface

[no] fast-reroute per-link use-candidate-only interface

fast-reroute per-link lfa-candidate interface {interface-name} interface

Configuration IOS-XR - OSPF

Command Router /

Interface

Comment

fast-reroute per-prefix load-sharing disable router

fast-reroute per-prefix priority-limit [critical|high|medium] router same or higher priority only will be calculated

fast-reroute per-link priority-limit [critical|high|medium] router

fast-reroute per-prefix remote-lfa tunnel mpls-ldp router

fast-reroute per-prefix remote-lfa maximum-cost <1-4294967295> router

fast-reroute {per-prefix|per-link} use-candidate-only router

fast-reroute per-prefix tiebreaker {downstream | lc-disjoint | lowest-

backup-metric | lowest-backup-metric | primary-path | secondary-path} index <value>

router

Configuration IOS-XR - ISISCommand Router /

Interface

Comment

fast-reroute {per-link|per-prefix} Interface

fast-reroute per-prefix exclude interface {interface-name} Interface

fast-reroute per-prefix lfa-candidate interface {interface-name} Interface used for allowing TE tunnel (explicit-path)

other intf types are by default on the lfa-candidate list

fast-reroute per-prefix level {1-2} Interface both L1 and L2 can be enabled

fast-reroute per-prefix load-sharing disable Router

fast-reroute per-prefix priority-limit [critical|high|medium] Router same or higher priority only will be calculated

fast-reroute per-prefix use-candidate-only Router

fast-reroute per-prefix tiebreaker {downstream|lc-disjoint|lowest-

backup-metric|lowest-backup-metric|primary-path|secondary-path} index <value>

Router

fast-reroute per-prefix remote-lfa tunnel mpls-ldp Router

fast-reroute per-prefix remote-lfa maximum-cost <1-4294967295> Router

Configuration IOS-XR - ISIS

Command Router /

Interface

Comment

fast-reroute per-link lfa-candidate interface {interface-name} Interface

fast-reroute per-link exclude {interface-name} Interface

fast-reroute per-link level {1-2} Interface both L1 and L2 can be enabled

fast-reroute per-link priority-limit [critical|high|medium] Router same or higher priority only will be calculated

fast-reroute per-link use-candidate-only Router

Default Tie Breaking ISIS - IOSTie-Breaker option Description Default values

IOS ISIS

Comment


primary-path (PrimPath) Prefer primary over secondary path 20 Backup is member of

ECMP set

lowest-backup-path-metric Prefer lower metric 30 The metric of the backup

node to D might be higher

than metric of S to D

linecard-disjoint (LC Dj) Prefer path using different linecard 40 Different linecard means

also different interface,

hence this is link protecting


load-sharing (LoadShare) Distribute remaining candidates among prefixes sharing

the protected path


This is the catch-at-the-end

policy



Default Tie Breaking OSPF – IOS-XR

Tie-Breaker option Description Default values

IOS-XR OSPF

Comment

node-protecting 40

lc-disjoint Prefer path using different linecard 30 Different linecard means also

different interface, hence this

is link protecting

lowest-backup-metric Prefer lower metric 20

primary-path Prefer primary over secondary path 10 Prefer primary over

secondary path

Downstream Prefer node closer to D than S 0

SRLG-disjoint Prefer LFA not sharing the same Share Link

Group

0

secondary-path Prefer secondary over primary path 0

load-sharing (LoadShare) Distribute remaining candidates among

prefixes sharing the protected path

255 Can be disabled

0 = not considered

Default Tie Breaking ISIS – IOS-XRTie-Breaker option Description Default values

IOS-XR ISIS

Comment

primary-path (PrimPath) Prefer primary over secondary path 10 Backup is member of

ECMP set








load-sharing (LoadShare) Distribute remaining candidates among prefixes sharing

the protected path


This is the catch-at-the-end

policy

srlg (SRLG) Prefer LFA not sharing the same Share Link Group - Disabled by default



Default Tie Breaking EIGRP– IOS

Tie-Breaker option Description Default values

IOS OSPF

Comment


interface-disjoint (IntfDj) Prefer path over other interface than protected one 20







Troubleshooting ISIS - IOS

R1#show isis fast-reroute summary

Tag null:

Microloop Avoidance State: Disabled

IPv4 Fast-Reroute Protection Summary:

Prefix Counts: Total Protected Coverage

High priority: 0 0 0%

Normal priority: 30 26 86%

Total: 30 26 86%

Troubleshooting ISIS - IOSrouter#show isis rib 10.1.100.7 255.255.255.255

IPv4 local RIB for IS-IS process one

IPV4 unicast topology base (TID 0, TOPOID 0x0) =================

Repair path attributes:

DS - Downstream, LC - Linecard-Disjoint, NP - Node-Protecting

PP - Primary-Path, SR - SRLG-Disjoint

10.1.100.7/32

[115/L1/20] via 10.1.5.7(GigabitEthernet1/4), from 10.1.100.7, tag 0, LSP[6/17]

(installed)

repair path: 10.1.6.7(GigabitEthernet1/5) metric:20 (PP,DS,SR) LSP[6]

[115/L1/20] via 10.1.6.7(GigabitEthernet1/5), from 10.1.100.7, tag 0, LSP[6/17]

(installed)

repair path: 10.1.5.7(GigabitEthernet1/4) metric:20 (PP,DS,SR) LSP[6]

repair path attributes

Troubleshooting ISIS - IOS

router#debug isis fast-reroute path-selection ?

<1-199> Access list of prefixes

<1300-2699> Access list (expanded range)

level-1 Apply to Level 1

level-2 Apply to Level 2

terse Minimal fast-reroute path selection debug

<cr>

Limit output by using ACL when

debugging

fSPF runs

500 ms after SPF

per-level

debug isis fast-reroute path-selection

show isis fast-reroute remote-lfa tunnels

Troubleshooting Per-Link LFA – IOS-XR

RP/0/RP1/CPU0:PE1#show ospf neighbor 10.1.100.7

* Indicates MADJ interface

Neighbors for OSPF ldg

Neighbor 10.1.100.7, interface address 10.1.2.7

In the area 0 via interface GigabitEthernet0/0/4/0

Neighbor priority is 1, State is FULL, 6 state changes

DR is 0.0.0.0 BDR is 0.0.0.0

Options is 0x52

LLS Options is 0x1 (LR)

Dead timer due in 00:00:32

Neighbor is up for 00:07:30

Number of DBD retrans during last exchange 0

Index 2/2, retransmission queue length 0, number of retransmission 0

First 0(0)/0(0) Next 0(0)/0(0)

Last retransmission scan length is 0, maximum is 0

Last retransmission scan time is 0 msec, maximum is 0 msec

LFA Info: Interface GigabitEthernet0/0/0/3, Next-Hop 10.1.11.3, Neighbor ID 10.1.100.3, revision 48

LS Ack list: NSR-sync pending 0, high water mark 0

Date post:	09-Mar-2018
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IP LFA (Loop-Free-Alternate): Architecture and … the MPLS (TE) Overhead = scalability ~50 ms...

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