The MPLS WG Archive

[Ina Minei <ina@juniper.net>]

	"label 0 is prepended" means label 0 is added to the bottom of the
stack, so there is no conflict with 3032.

	The authors wanted to ensure that the lsping probe arrives at the
endpoint of the tunnel as a labeled packet with label 0 rather than an ip
packet.

			Ina


On Tue, 20 May 2003, lidefeng wrote:

> In section "5.3. Procedures at the ingress LSR" of
> draft-ietf-mpls-lsp-ping-02.txt,it states that"To test an LSP that carries
> non-IP traffic, before injecting ICMP and MPLS ping messages into the LSP,
> the IPv4 Explicit NULL label should be prepended to such messages. The
> ingress and egress LSR's must follow the procedures defined in
> [LABEL-STACK]."
>
> While in RFC 3032(section 2.1. Encoding the Label Stack),the definition of
> IPv4 Explicit NULL label is as following:
>
>            i. A value of 0 represents the "IPv4 Explicit NULL Label".
>               This label value is only legal at the bottom of the label
>               stack.  It indicates that the label stack must be popped,
>               and the forwarding of the packet must then be based on the
>               IPv4 header.
>
> It is explicitly stated that " This label value is only legal at the bottom
> of the label  stack." ,while in  draft-ietf-mpls-lsp-ping-02.txt,it states
> that this "IPv4 Explicit NULL label should be prepended to such messages",Is
> it inconsistent with each other?
>
> Another question is that why shouls this IPv4 Explicit NULL label should be
> prepended to such messages?
>
> TIA
>
> Defeng Li
>
> Huawei technologies
>