set-overload

Function

The set-overload command sets the overload bit for non-pseudonode LSPs.

The undo set-overload command clears the set overload bit.

By default, the overload bit is not set.

Format

set-overload

set-overload { allow { interlevel | external } ^* }

set-overload { on-startup [ timeout1 | start-from-nbr system-id [ timeout1 [ timeout2 ] ] | wait-for-bgp [ timeout1 ] ] [ route-delay-distribute timeout4 ] [ send-sa-bit [ timeout3 ] ] [ route-max-metric ] }

undo set-overload

Parameters

Parameter	Description	Value
allow	Enables the device to advertise IP prefixes. By default, IP prefixes are not advertised when the system enters the Overload state.	-
interlevel	Enables the device to advertise the IP prefixes learned from IS-IS of different levels when allow is configured.	-
external	Enables the device to advertise the IP prefixes learned from other protocols when allow is configured.	-
on-startup	Sets the overload bit within the specified period when a device is restarted or faulty.	-
timeout1	Specifies the period during which the overload bit remains set after the system is started.	The value is an integer ranging from 5 to 86400, in seconds. The default value is 600s.
start-from-nbr system-id	Sets the overload bit based on the status of the neighbor with the specified system ID.	The value is a string of 1 to 19 case-sensitive characters, spaces not supported.
timeout2	Specifies the period during which the overload bit remains set based on the neighbor status. If the specified neighbor does not go Up within timeout2, the overload bit of the system remains set over a period specified by timeout2. If the specified neighbor goes Up within timeout2, the overload bit of the system remains set over a period specified by timeout1.	The value is an integer ranging from 5 to 86400, in seconds. The default value is 1200.
wait-for-bgp	Sets the length of the overload flag bit to wait for BGP to complete convergence. The specific setting time should be adjusted according to the BGP convergence time in the device.	-
route-delay-distribute timeout4	Indicates delayed route advertisement. After the device is restarted, in order to prevent other devices from using the old LSP to calculate the route to the restart device, traffic is introduced to the restart device. This parameter needs to be configured together with the send-sa-bit parameter. When used alone, there may be residual LSPs in the network, which may not achieve the purpose of avoiding traffic to restart the device here.	The value is an integer ranging from 5 to min (timeout1, 1000), in seconds.
send-sa-bit	Enables the device to send the Hello packets with the SA bit after the device restarts. When a neighbor device receives a Hello packet in which the SA bit is set to TRUE from the restarted node, the LSP sent by the restarted node no longer carries the adjacency information. In this manner, traffic does not reach the restarted node. The SA bit is the Supperess Adjacency Bit field carried in the Restart Signaling flag TLV of an IS-IS Hello packet. The SA bit is used to prevent a faulty device from establishing adjacencies with neighboring devices.	-
timeout3	Specifies the period during which the overload bit remains in Hello packets after the device is started.	The value is an integer ranging from 5 to 600, in seconds. The default value is 30 seconds.
route-max-metric	Set the local originating route to the maximum metric.	-

Views

IS-IS view

Default Level

2: Configuration level

Task Name and Operations

Task Name	Operations
isis	write

Usage Guidelines

Usage Scenario

If the system cannot store new LSPs or synchronize the LSDB normally because of memory shortage, the routes calculated by this system are incorrect. In this case, the system automatically enters the Overload state, regardless of whether the set-overload command is run.

After the set-overload command is run, an IS-IS process enters the Overload state when it is started or restarted and instructs other devices not to use it for traffic forwarding.

On a BGP network, if a device is newly added to the network or a device is restarted, and the device is used as a forwarding node, traffic loss occurs because IS-IS route convergence is faster than BGP route convergence. To prevent this problem, run the set-overload command with the wait-for-bgp parameter specified and configure a timer for the parameter. In this way, the device notifies other devices that it is in the Overload state and instructs them not to use it as a forwarding node until the overload (OL) bit in LSPs is cleared when the timer expires.

To prevent the local device that is started for the first time or becomes faulty from participating the SPF calculation performed by other devices, run the set-overload command on the local device without on-startup specified. In this manner, the system immediately sets the overload bit in the LSP to be sent. To clear the overload bit, run the undo set-overload command.

To prevent the local device that is restarted from participating the SPF calculation performed by other devices, run the set-overload command with on-startup specified on the local device.

With on-startup specified, you can configure route-delay-distribute timeout4 to control delayed route advertisement. After route-delay-distribute timeout4 is configured and the device is restarted, route advertisement is delayed until timeout4 expires or the overload bit is cleared. After the device is restarted, if routes need to be advertised when timeout4 has not yet expired, use any of the following methods:

Perform a master/slave main control board switchover.
Run the command again, without route-delay-distribute specified.
Run the reset isis all command.
After the on-startup parameter is specified in this command, you can specify the route-max-metric parameter to change the metrics of locally originated routes to the maximum value. After the device configured with the route-max-metric parameter is restarted, the metrics of the locally originated routes on the device are changed to the maximum value. The metrics of these routes can be restored to the original value only when the timeout1 timer expires or the overload bit is set to 0. After the device is restarted, if the original metrics of these routes need to be restored before the timeout1 timer expires, you can use either of the following methods:
Run the command again with the on-startup parameter specified, but do not specify the route-max-metric parameter.
Run the reset isis all command.
Running this command may cause a temporary link flapping. Therefore, exercise caution when running the command.

Prerequisites

An IS-IS process has been created.

Configuration Impact

After the set-overload command is run:

If on-startup is specified, the LSPs with the overload bit set are flooded on the network only when the IS-IS process is restarted.
If on-startup is not specified, the system immediately sets the overload bit in the LSPs to be sent. After the overload bit is set, other devices do not consider the local device during SPF calculation, but the direct routes to the local device are not ignored.

Precautions

When a device is experiencing a memory shortage, the system automatically sets the overload bit in the LSP to be sent, regardless of whether the set-overload command is run.

After the device is restarted, if you change the value of timeout4 when it has not yet expired, the current value is still used until the timer expires.

Using the delayed route advertisement function only when a backup path is available is recommended.

If a TE LSP uses the local device as a transit node before the set-overload command is run, the TE LSP is not torn down and re-established and still uses the local device as a transit node after the set-overload command is run; if the local device is restarted after the command is run and fast convergence is not configured on the ingress of the RSVP-LSP, TE LSP forwarding fails, and services are affected. Therefore, the mpls te path-selection overload command needs to be run on the ingress of the RSVP-LSP before the device is restarted.

Example

# Configure IS-IS process 1 to enter the Overload state during the startup, allow IS-IS to advertise the IP prefixes learned from IS-IS of different levels, and prevent IS-IS from advertising the IP prefixes learned from other protocols.

<HUAWEI> system-view
[~HUAWEI] isis
[*HUAWEI-isis-1] set-overload on-startup allow interlevel

# Configure IS-IS process 1 to enter the Overload state during the startup, and configure the local device to maintain the Overload state for 300 seconds after it establishes the neighbor relationship with neighbor 0000.0000.0002 within 1000 seconds during which the system starts.

<HUAWEI> system-view
[~HUAWEI] isis
[*HUAWEI-isis-1] set-overload on-startup start-from-nbr 0000.0000.0002 300 1000

# Set the overload bit for IS-IS process 1.

<HUAWEI> system-view
[~HUAWEI] isis
[*HUAWEI-isis-1] set-overload