The MPLS WG Archive

[Kireeti Kompella <kireeti@juniper.net>]

Hi,

On Thu, 28 Aug 2003, lidefeng wrote:

> In appendix 4: Diagnostic tools,it states that,

I'll answer this, as it relates to draft-ietf-mpls-lsp-ping-03.txt.

> When we execute MPLS PING or MPLS TRACEROUTE, If the egress LSR for the FEC
> Stack being pinged does not support MPLS ping, then no LSP-PING reply will
> be sent.

If an lsp ping fails, the next step is to find out why.  A good first
step is to check that the egress indeed supports lsp ping; if not, the
ping was not much use.  Note that in the case of ping, transit routers
only need to support MPLS forwarding.

> If in trace mode, a transit LSR does not support MPLS ping, then
> no reply will be forthcoming from that LSR for some TTL, say n.

Read section 4.6 of draft-ietf-mpls-lsp-ping-03.txt.

> Under such circumstance,how I distinguish the scenario that there is
> something wrong along the LSP from the scenario that there is Non-compliant
> Routes along the LSP .i.e. if the PING dosen't work,how do I know if it is
> because the existence of the non-compliant Routes?

If a router doesn't implement (regular) ping (or chooses to discard
icmps), how do you distinguish the scenario that there is something
wrong with IP routing, or that there are "non-compliant" IP routers
along the path?  ("Non-compliance" is a fairly common occurrence
today, thanks to firewall filters.)

The answer is, you don't.  The solution (in the case of lsp ping) is,
make sure that the egress you want to ping is compliant.

Kireeti.