[c-nsp] P2MP LSPs :: TailEnd/Bud nodes behavior

[Phil Bedard]

In the Juniper case you can get around the double replication on the M/T
by using a tunnel services PIC and using a tunnel interface to terminate
the P2MP LSP.   Just a limitation of the platforms.

Phil 

On 2/28/11 10:44 AM, "Egor Zimin" <lesnix at gmail.com> wrote:

>Hello, guys
>
>Today I noticed very interesting difference in implementation of P2MP
>LSPs by Cisco and Juniper.
>The difference is related to explicit/implicit-null behavior of S2L
>Sub-LSP tailend routers:
>Cisco implementation:
>(http://www.cisco.com/en/US/docs/ios/mpls/configuration/guide/mp_te_p2mp_p
>s6922_TSD_Products_Configuration_Guide_Chapter.html)
>---
>The tailend routers allocate unreserved labels, which are greater than
>15 and do not include implicit or explicit null labels.
>---
>
>In Juniper's implementation tailend allocates implicit/explicit null
>label as a usual.
>As a consequence of this, (it looks like) we can have unnecessary
>replication before "Bud" nodes.
>
>For example:
>Let's consider this configuration:
>###
>label-switched-path LSP-P2MP-16--19 {
>    to 10.245.87.19;
>    p2mp TREE1;
>}
>label-switched-path LSP-P2MP-16--18 {
>    to 10.245.87.18;
>    p2mp TREE1;
>}
>label-switched-path LSP-P2MP-16--15 {
>    to 10.245.87.15;
>    p2mp TREE1;
>}
>label-switched-path LSP-P2MP-16--17 {
>    to 10.245.87.17;
>    p2mp TREE1;
>}
>###
>> show mpls lsp p2mp ingress
>Ingress LSP: 1 sessions
>P2MP name: TREE1, P2MP branch count: 4
>To              From            State Rt P     ActivePath       LSPname
>10.245.87.17    10.245.87.16    Up     0 *
>LSP-P2MP-16--17
>10.245.87.15    10.245.87.16    Up     0 *
>LSP-P2MP-16--15
>10.245.87.18    10.245.87.16    Up     0 *
>LSP-P2MP-16--18
>10.245.87.19    10.245.87.16    Up     0 *
>LSP-P2MP-16--19
>Total 4 displayed, Up 4, Down 0
>###
>As you can see, there are four leaves. Three bottom leaves use the
>same downstream interface:
>###
>> show rsvp session p2mp detail | match "PATH sentto"
>  PATH sentto: 10.245.87.146 (xe-0/0/2.0) 4 pkts
>  PATH sentto: 10.245.87.149 (xe-0/0/1.0) 2 pkts
>  PATH sentto: 10.245.87.149 (xe-0/0/1.0) 2 pkts
>  PATH sentto: 10.245.87.149 (xe-0/0/1.0) 3 pkts
>###
>> show rsvp session p2mp
>Ingress RSVP: 18 sessions
>P2MP name: TREE1, P2MP branch count: 4
>To              From            State   Rt Style Labelin Labelout LSPname
>10.245.87.17    10.245.87.16    Up       0  1 SE       -        3
>LSP-P2MP-16--17
>10.245.87.15    10.245.87.16    Up       0  1 SE       -        3
>LSP-P2MP-16--15
>10.245.87.18    10.245.87.16    Up       0  1 SE       -   309200
>LSP-P2MP-16--18
>10.245.87.19    10.245.87.16    Up       0  1 SE       -   309200
>LSP-P2MP-16--19
>Total 4 displayed, Up 4, Down 0
>###
>
>As you can see, we have two different out labels (3 and 309200) for
>the same P2MP LSP. Label 3 is allocated by node 10.245.87.15 because
>of PHP.
>
>Can anybody explain, what IETF speaks about this case ? Must tailend
>routers allocate unreserved label or not ? I can't find any mention of
>this case in RFCs (4875, 4461).
>
>-- 
>Best regards,
>Egor Zimin
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