IS-IS Microloop-Avoidance Commands
This chapter describes the IS-IS microloop-avoidance commands:
microloop-avoidance
Use this command to enable microloop avoidance using ordered FIB (oFIB) for an ISIS process.
Use the no form of this command to disable microloop avoidance for an ISIS process.
Microloop avoidance will be enabled with default hold-timer and max-fib values if it is not configured by the user:
• Default value of hold-timer is 6 seconds
• Default value for max-fib is 2 seconds
Microloop avoidance has to be enabled in conjunction with a fast reroute (FRR) mechanism such as TILFA that converts a sudden link or node failure into a non-urgent topology change by having complete repair path for all affected destinations. With microloop-avoidance, the convergence will be slower compared to traditional (SPF) convergence mechanisms. So, when there is any failure of a link or a set of links that are not protected using an FRR mechanism, it is advised to use conventional SPF (faster) mode of operation to minimize packet loss during convergence/reconvergence.
Command Syntax
microloop-avoidance(flex-algo|hold-timer|level-1|level-2|max-fib|segment-routing
)
no microloop-avoidance(flex-algo|hold-timer|level-1|level-2|max-fib|segment-routing
)
Parameters
flex-algo
Specifies the algorithm number used for Flexible Algorithm
hold-timer
Specifies the hold-timer value in seconds.
level-1
Applies the configuration to IS-IS Level-1 only.
level-2
Applies the configuration to IS-IS Level-2 only.
max-fib
Specifies the max-fib value for microloop-avoidance.
segment-routing
Enables Segment Routing functionality.
Default
None
Command Mode
ISIS router mode
Applicability
This command was introduced in OcNOS version 6.3.0. Added parameters flex-algo, hold-timer, max-fib, and segment-routing
in OcNOS version 6.6.1.
Examples
#configure terminal
(config)#router isis 100
(config-router)#microloop-avoidance level-1
(config-router)#microloop-avoidance level-2
(config-router)#
#configure terminal
(config)#router isis 100
(config-router)#no microloop-avoidance level-1
(config-router)#no microloop-avoidance level-2
(config-router)#
microloop-avoidance flex-algo
Use this command to enable microloop avoidance using ordered FIB (oFIB) for an IS-IS Flexible Algorithm (Flex-Algo) instance.
Use the no form of this command to disable microloop avoidance for a Flex-Algo instance.
Microloop avoidance ensures loop-free convergence during topology changes by delaying FIB updates in a controlled sequence. When used with Flex-Algo, this feature applies the same loop-prevention behavior within the topology defined by that algorithm (for example: specific metric types, link affinities).
Command Syntax
microloop-avoidance flex-algo (128-255)(level-1|level-2)
no microloop-avoidance flex-algo (128-255)(level-1|level-2)
Parameters
128-255
Specifies the flex- algo instance range for which microloop-avoidance is to be enabled.
level-1
Applies microloop-avoidance to IS-IS Level-1 routing under the specified Flex-Algo.
level-2
Applies microloop-avoidance to IS-IS Level-2 routing under the specified Flex-Algo.
Defaults
None
Command Mode
ISIS router mode
Applicability
This command was introduced in OcNOS version 6.6.1.
Examples
#configure terminal
(config)#router isis 1
(config-router)#microloop-avoidance flex-algo 129 level-1
(config-router)#microloop-avoidance flex-algo 130 level-2
#configure terminal
(config)#router isis 1
(config-router)#no microloop-avoidance flex-algo 129 level-1
(config-router)#no microloop-avoidance flex-algo 130 level-2
microloop-avoidance hold-timer
Use this command to configure the hold-timer valuefor microloop avoidance.
Use the no form of this command to return to the default hold-timer value for microloop avoidance.
Hold-timer value means the time that router will wait after receiving first LSP update with a topology change, to group all related LSP updates together to process using oFIB.
Microloop avoidance has to be enabled first for the particular level before configuring the hold-timer.
Hold-timer value must be configured same across all routers in the network to get the desired results.
Command Syntax
microloop-avoidance hold-timer (1-60) (level-1|level-2)
no microloop-avoidance hold-timer (level-1|level-2)
Parameters
1-60
Specifies the hold-timer value in seconds.
level-1
Applies the configuration to IS-IS Level-1 only.
level-2
Applies the configuration to IS-IS Level-1 only.
Defaults
Default value for hold-timer is 6 seconds
Command Mode
ISIS router mode
Applicability
This command was introduced in OcNOS version 6.3.0.
Examples
#configure terminal
(config)#router isis 100
(config-router)#microloop-avoidance hold-timer 3 level-1
(config-router)#microloop-avoidance hold-timer 3 level-2
(config-router)#
#configure terminal
(config)#router isis 100
(config-router)#no microloop-avoidance hold-timer level-1
(config-router)#no microloop-avoidance hold-timer level-2
(config-router)#
microloop-avoidance max-fib
Use this command to configure the max-fib value for microloop avoidance.
Use the no form of this command to return to the default max-fib value for microloop avoidance.
The max-fib value is a network-wide constant that reflects the maximum time required to update a FIB irrespective of the change required. This value will be further multiplied by the oFIB RANK to get the actual FIB update delay time.
Microloop avoidance has to be enabled first for the particular level before configuring max-fib.
Max-fib value must be configured same across all routers in the network to get the desired results.
Command Syntax
microloop-avoidance max-fib (1-60) (level-1|level-2)
no microloop-avoidance max-fib (level-1|level-2)
Parameters
1-60
Specifies the max-fib value in seconds
level-1
Applies the configuration to IS-IS Level-1 only.
level-2
Applies the configuration to IS-IS Level-2 only.
Default
2 seconds
Command Mode
ISIS router mode
Applicability
This command was introduced in OcNOS version 6.3.0.
Examples
#configure terminal
(config)#router isis 100
(config-router)#microloop-avoidance max-fib 3 level-1
(config-router)#microloop-avoidance max-fib 3 level-2
(config-router)#
#configure terminal
(config)#router isis 100
(config-router)#no microloop-avoidance max-fib level-1
(config-router)#no microloop-avoidance max-fib level-2
microloop-avoidance segment-routing
Use this command to configure a SR micro-loop avoidance under IS-IS Segment Routing (SR) mode.
Use the no form of this command to disable microloop avoidance for under IS-IS Segment Routing (SR) mode.
When microloop avoidance is enabled under Segment Routing, the router ensures loop-free convergence by controlling FIB updates across the network during topology changes.
Command Syntax
microloop-avoidance segment-routing (level-1 | level-2)(proto ipv4|ipv6 fib-delay) <100-300000>
no microloop-avoidance segment-routing (level-1 | level-2)(proto ipv4|ipv6)
Parameters
level-1
Applies Segment Routing microloop-avoidance logic only to IS-IS Level-1.
level-2
Applies Segment Routing microloop-avoidance logic only to IS-IS Level-2.
prot0
Specifies the protocol family (IPv4 or IPv6) to which microloop avoidance will be applied.
ipv4
Specifies the IPv4 protocol family to which microloop avoidance will be applied.
ipv6
Specifies the IPv6 protocol family to which microloop avoidance will be applied.
100–300000
Sets the delay in milliseconds for updating the Forwarding Information Base (FIB). This delay helps prevent microloops by controlling the rate at which FIB changes are applied.
Default
If fib-delay is not configured, default fib-delay of 1500ms(1.5 sec) is configured.
Command Mode
ISIS router mode
Applicability
This command was introduced in OcNOS version 6.6.1.
Examples
#configure terminal
(config)#router isis 1
(config-router)#microloop-avoidance segment-routing level-1 proto ipv4 fib-delay 100
(config-router)#microloop-avoidance segment-routing level-2 proto ipv6 fib-delay 1000
#configure terminal
(config)#router isis 1
(config-router)#no microloop-avoidance segment-routing level-1 proto ipv4
(config-router)#no microloop-avoidance segment-routing level-2 proto ipv6
show isis microloop-avoidance
Use this command to display microloop avoidance FSM states, timer values, and the oFIB route table.
Command Syntax
show isis microloop-avoidance (flex-algo|level-1|level-2|segment-routing) (previous-info|detail|)
Parameters
flex-algo
Specifies the algorithm number used for Flexible Algorithm
detail
Display detailed information for one or both levels.
level-1
Filters the output to show microloop avoidance data for IS-IS Level-1 topology.
level-2
Filters the output to show microloop avoidance data for IS-IS Level-2 topology.
previous-info
Provides the details of previous oFIB executions.
segment-routing
Displays microloop avoidance configuration and state for IS-IS SR instances.
Command Mode
Privileged Exec mode
Applicability
This command was introduced in OcNOS version 6.3.0. Added parameters flex-algo and previous-info in OcNOS version 6.6.1.
Example
conos#show isis microloop-avoidance detail
Tag 1: VRF : default
Level-1 status:
FSM State: OFIB_STABLE
Level-2 status:
FSM State: OFIB_HOLDING_DOWN
Event type: Neighbor Down
Configured hold-timer: 6 Configured max-fib: 2
Rank: 2
Near end: 0000.0000.0004.00 Far end:0000.0000.0005.01
Hold-down timer running: Yes Time Remaning: 00:00:03.644
Delay timer running: No
oFIB Route Table:
Destination Metric Next-Hop Interface Tag
L2 2.2.2.2/32 30 3.5.0.3 eth2 0
Src: 0000.0000.0002
L2 2.4.0.0/24 30 3.5.0.3 eth2 0
Src: 0000.0000.0002
L2 2.6.0.0/24 30 3.5.0.3 eth2 0
Src: 0000.0000.0002
L2 3.4.0.0/24 40 3.5.0.3 eth2 0
Src: 0000.0000.0004
L2 4.4.4.4/32 40 3.5.0.3 eth2 0
Src: 0000.0000.0004
ocnos# show isis microloop-avoidance previous-info
Tag 1: VRF : default
Level-2 status:
Last Event type: Neighbor Down
Started at: 25-Jun-2025 13:23:51.873, Completed at: 25-Jun-2025 13:23:57.873
Near end: 0000.0000.0044.02, Far end: 0000.0000.0044.02
Hold-timer: 6s, Max-fib: 2s
Computed Rank: 0, Delay time: 00:00:06
Total Delayed Routes Count: 2
Last Delayed Routes:
4.4.4.4/32
7.7.7.77/32
ocnos#show isis microloop-avoidance previous-info
Tag 1: VRF : default
Level-2 status:
Last Event type: Neighbor Up
Started at: 25-Jun-2025 13:24:16.693, Completed at: 25-Jun-2025 13:24:23.694
Near end: 0000.0000.0044.02, Far end: 0000.0000.0044.02
Hold-timer: 6s, Max-fib: 2s
Computed Rank: 1, Delay time: 00:00:08
Total Delayed Routes Count: 2
Last Delayed Routes:
4.4.4.4/32
7.7.7.77/32
ocnos#show isis microloop-avoidance segment-routing info
IS-IS level-1 proto-IPv4, microloop-avoidance segment-routing is enabled
fib-delay 10000 ms.
algorithm_num: 0
microloop-avoidance segment-routing SPF stage: Active
Route:44.44.44.44/32
Eligible vertex:PE2.00-00
pnode: 0000.0001.0030.00
qnode: 0000.0001.0044.00
sid list:
sid: 16030
sid: 24320
next-hop:
ifindex: 10101
ip_addr: 10.1.1.2