ipv6 default-route-advertise

Function

The ipv6 default-route-advertise command enables a device to advertise a default IPv6 route.

The undo ipv6 default-route-advertise command disables a device from advertising a default IPv6 route.

By default, a device does not advertise default IPv6 routes.

Format

undo ipv6 default-route-advertise

Parameters

Parameter	Description	Value
always	Enables an IS-IS device to advertise the default IPv6 route unconditionally. This parameter is specified by default when the ipv6 default-route-advertise command is run. In this case, if the avoid-learning parameter is not specified, the device is allowed to calculate the IS-IS default IPv6 routes advertised by other devices, which may cause routing loops.	-
match	When a device has an active default IPv6 route, which belongs to a process of another routing protocol or belongs to another IS-IS process, this parameter enables the device to advertise the default route through a local LSP. However, if the avoid-learning parameter is not specified, the device is allowed to calculate the IS-IS default routes advertised by other neighbors. As a result, the default route that belongs to the process of another routing protocol or belongs to another IS-IS process on the local device may become inactive. If this problem occurs, the device no longer advertises the default route through a local LSP.	-
default	If a default IPv6 route generated by other routing protocols or other IS-IS processes exists in the routing table, the default IPv6 route is advertised through an LSP.	-
route-policy route-policy-name	Specifies the name of a route-policy. If the routes that match the route-policy include non-default routes, a default IPv6 route that belongs to a process of another routing protocol, or a default IPv6 route that belongs to another IS-IS process, the device advertises a default route through a local LSP. In this case, if the avoid-learning parameter is not specified, the device is allowed to calculate the IS-IS default routes advertised by other devices, which may cause routing loops. If only the default IPv6 route in the current local IS-IS process matches the route-policy, the device does not advertise a default route through a local LSP.	The name is a string of 1 to 200 case-sensitive characters, with spaces not supported. When double quotation marks are used around the string, spaces are allowed in the string.
route-filter route-filter-name	Specifies the name of a route-filter. If the routes that match the route-filter include non-default routes, a default IPv6 route that belongs to a process of another routing protocol, or a default IPv6 route that belongs to another IS-IS process, the device advertises a default IPv6 route through a local LSP. In this case, if the avoid-learning parameter is not specified, the device is allowed to calculate the IS-IS default routes advertised by other devices, which may cause routing loops. If only the default IPv6 route in the current local IS-IS process matches the route-filter, the device does not advertise a default IPv6 route through a local LSP.	The value is a string of 1 to 200 case-sensitive characters, spaces not supported. If parameters are included in the referenced route-filter, specify values for them in the format of (var1, var2, ...var8) behind the route-filter name. A maximum of eight parameters can be specified, and each value ranges from 1 to 200 characters.
cost cost	Specifies a cost for the default route.	The value is an integer ranging from 0 to 4261412864.
tag tag	Specifies a tag for the default route to be advertised.	The value is an integer ranging from 1 to 4294967295.
level-1	Sets the level as Level-1.	-
level-2	Sets the level as Level-2.	-
level-1-2	Sets the level as Level-1-2. If you do not specify a level, Level-2 routes are generated by default.	-
avoid-learning	Prevents the specified IS-IS process from adding a learned default IPv6 route to the routing table. If the local device has advertised a default route in the specified IS-IS process, the device no longer adds a learned IS-IS default route to the routing table. If the device has not advertised a default route in the specified IS-IS process, the device can still add a learned IS-IS default route to the routing table even if avoid-learning is specified.	-
learning-avoid-loop	Generates a backup route for a default route to prevent routing loops.	-

Views

IS-IS view

Default Level

2: Configuration level

Task Name and Operations

Task Name	Operations
isis	write

Usage Guidelines

Usage Scenario

This command can be run on a Level-1 or Level-2 device.

By using a route-policy, you can configure IS-IS to generate default routes only when there is a matched entry in the routing table.

If the apply isis level-1 command is used in the route-policy view, IS-IS can generate default routes in Level-1 LSPs.
If the apply isis level-2 command is used in the route-policy view, IS-IS can generate default routes in Level-2 LSPs.
If the apply isis level-1-2 command is used in the route-policy view, IS-IS can generate default routes in Level-1 and Level-2 LSPs.
On a network, at least two devices (A and B for example) advertise the default route. If device C preferentially selects the default route advertised by device A and sends traffic destined for the default route, to device A, but the outbound interface of the specific route on device A fails, device C keeps sending the traffic to device A because device C fails to detect the fault in time. Due to the outbound interface failure, device A sends the traffic back to device C, leading to a routing loop. To prevent this problem, specify the learning-avoid-loop parameter when configuring the default route on device A so that a backup path (passing through device B) is generated for the default route.

Prerequisites

The ipv6 default-route-advertise command takes effect only after IPv6 is enabled for the IS-IS process. For details, see isis ipv6 enable.

Precautions

The learning-avoid-loop parameter takes effect only after the ipv6 frr and segment-routing ipv6 locator commands are run.
The learning-avoid-loop parameter takes effect only for default route on a network, and two or more devices must advertise the default route on the network.
The learning-avoid-loop parameter may not be applicable to all scenarios. You need to determine a specific loop prevention method based on the actual networking scenario.

Example

# Configure the device to generate the default IPv6 routes in Level-1-2 LSPs.

<HUAWEI> system-view
[~HUAWEI] isis 1
[*HUAWEI-isis-1] ipv6 enable
[*HUAWEI-isis-1] ipv6 default-route-advertise