Hi Joel, I now see your concern. The "private" word in draft is not correct, I will remove it. The original motivation of "draft-relay-reply" is from the scenario where IP address distribution is restricted among AS or IGP area. And the IP address is not private address. As I know, most deployed inter-AS or inter-area MPLS LSP is in the network without private IP address. Regards Lizhong > -----Original Message----- > From: Joel M. Halpern [mailto:jmh@xxxxxxxxxxxxxxx] > Sent: 2014年10月22日 10:15 > To: Lizhong Jin > Cc: gen-art@xxxxxxxx; mpls@xxxxxxxx; ietf@xxxxxxxx; 'draft-ietf-mpls-lsp-ping- > relay-reply.all' > Subject: Re: [mpls] [Gen-art] review: draft-ietf-mpls-lsp-ping-relay-reply-04 > > The problem is that the original source A, that we are trying to reach with a > reply, has an address that appears to the responder X to be routable. But > the destination that is reached by that address is either a black hole or some > other entity using the same address. > > The reason for the duplication is that, as described in the draft, the source > address for A is a private address. That same address may well be reachable > according to the routing table at X. But it won't get to A. > > If the problem is something other than private addressing preventing > reachability, it is likely there is still a mistaken routability problem, but I can > not illustrate the failure without some other case being described. > > Yours, > Joel > > On 10/21/14, 10:06 PM, Lizhong Jin wrote: > > Inline, thanks. > > > >> -----Original Message----- > >> From: Joel M. Halpern [mailto:jmh@xxxxxxxxxxxxxxx] > >> Sent: 2014年10月22日 0:06 > >> To: lizho.jin@xxxxxxxxx > >> Cc: gen-art@xxxxxxxx; mpls@xxxxxxxx; ietf@xxxxxxxx; > > draft-ietf-mpls-lsp-ping- > >> relay-reply.all > >> Subject: Re: [mpls] [Gen-art] review: > > draft-ietf-mpls-lsp-ping-relay-reply-04 > >> > >> In line. > >> > >> On 10/21/14, 10:36 AM, lizho.jin@xxxxxxxxx wrote: > >>> Hi Joel, see inline below, thanks. > >>> > >>> Lizhong > >>> > >>> > >>>> 2014.10.21，PM9:30，Joel M. Halpern <jmh@xxxxxxxxxxxxxxx> wrote ： > >>>> > >>>> If the process for this draft is to use the top address that can be > >>>> reached in the routing table, then there is a significant > >>>> probability that the original source address, which is always at > >>>> the top of the list, will be used. As such, the intended problem > >>>> will not be solved. > >>> [Lizhong] let me give an example to explain: the source address A is > >>> firstly added to the stack, then a second routable address B for > >>> replying AS is also added. The reply node will not use address A > >>> since it's not routable, then it will use address B. So it will work > >>> and I don't see the problem. > >> > >> The whole point of this relay mechanism, as I understand it, is to > >> cope > > with > >> the case when the responder X can not actually reach the source A. > >> Now suppose that the packet arrives at X with the Address stack A, B, ... > > X > >> examines the stack. The domain of A was numbered using net 10. > >> The domain of X is numbered using net 10. A's address is probably > > routable > >> in X's routing table. The problem is, that routing will not get to > >> A. X > > examines > >> the stack, determines that A is "routable", and sends the packet. > >> This > > fails to > >> meet the goal. > > [Lizhong] The source A you are referring is the initiator, right? The > > goal of relay mechanism is to reach the initiator. If X is routable to > > the initiator (address A), then it is great, other relay node in the > > stack will be skipped. > > If the source A you are referring is the interface address of one > > intermediate node, then I do not understand "routing will not get to > > A. X examines the stack, determines that A is "routable", and sends the > packet". > > Why routing will not get to A, but A is routable? > > > > Regards > > Lizhong > > > > > >> > >> Yours, > >> Joel > > > > > >