The MPLS WG Archive

[Alia Atlas <aatlas@avici.com>]

At 04:04 PM 12/19/2002 -0500, Curtis Villamizar wrote:
> > 1) Use explicit null label even though the traffic is IP, and detect 
> LSP-ping
> > packets from S=0 in the VPN label. This may require HW change, because 
> curren
> > t implementations don't look at S-bit.
> >
> > 2) Only push the PSN label, and encode the VPN  label in the echo-request.
> >
> > 3) In echo-request set the TTL=0 for VPN label, and detect the LSP-ping by
> > sending the TTL=0 packets to the OAM module. This may also require HW 
> change
> > as I am not sure current implementations check the TTL of the VPN label.
> >
> > My suggestion was the 2nd one. What method do you suggest?
> >
> > Thanks,
> > -Shahram
>
>
>I was suggesting you set TTL=1 on the VPN label and include an
>explicit null label, also with TTL=1.  Others can speak up if the
>change will be a problem.

Currently the incoming TTL, which I believe is that checked for the TTL 
expiring, is based upon the top incoming label.  I.e., if the PSN label is 
still on the packet when it reaches the egress, then its TTL would be used, 
rather than the TTL of the VPN label underneath.  Of course, if the PSN 
label is not there, because of PHP, then the incoming TTL would be that of 
the VPN label, and this could work - but that requires PHP :-(.

Alia