ttl-copymode

Function

Using the ttl-copymode command, you can specify the TTL propagation mode (pipe or uniform) for a multi-hop PW detection.

Using the undo ttl-copymode command, you can cancel the TTL propagation mode configured in the NQA view.

By default, the TTL propagation mode varies with products.

Format

ttl-copymode { pipe | uniform }

undo ttl-copymode

Parameters

Parameter	Description	Value
pipe	Sets the TTL propagation mode to pipe.	-
uniform	Sets the TTL propagation mode to uniform.	-

Views

NQA view

Default Level

2: Configuration level

Usage Guidelines

During the detection of a multi-hop PW, if the default TTL propagation mode on different devices is different, you need to specify the TTL propagation mode on the first hop of the PW. This command is used to detect PWE3 networks and BGP/MPLS IP VPN networks.

The TTL propagated in pipe and uniform modes is processed in different manners:

When receiving a packet carrying the TTL propagated in pipe mode, the system strips the outer tag of the packet, decreases the TTL in the inner tag by 1, and then sets the TTL in the outer tag to 255.
When receiving a packet carrying the TTL propagated in uniform mode, the system maps the TTL in the outer tag to the inner tag, decreases the TTL in the inner tag by 1, and then sets the TTL in the outer tag to the value of the TTL in the inner tag.

The ttl-copymode command makes sense only in the Trace test instances. In the case of a trace test instance, you need to first run the vpn-instance vpn-instance-name command to bind the NQA trace test instance with a VPN instance.

Example

# Configure the TTL propagation mode of packets in the NQA trace test instance as pipe.

<HUAWEI> system-view
[HUAWEI] nqa test-instance admin trace
[HUAWEI-nqa-admin-trace] test-type trace
[HUAWEI-nqa-admin-trace] vpn-instance voice
[HUAWEI-nqa-admin-trace] ttl-copymode pipe