1. LDP Extensions for RMR draft-esale-mpls-ldp-rmr- extensions
Resilient MPLS Rings
LDP Extensions for RMR draft-esale-mpls-ldp-rmr- extensions
IETF 97
Santosh Esale
Kireeti Kompella (presenter)

2. LDP deficiencies on ring
Single (shortest path) LDP LSP
After failure, SPF changes nexthop of same LSP to other side of ring, resulting in micro-loops
Optimal utilization of all of the ring bandwidth is hard
Ring is worst topology for LFA protection
LDP over RSVP protection has same limitation as described in RSVP-TE extensions
More in architecture document - draft-ietf-mpls-rmr

3. Ring LSP capability
RMR LSP support for a LSR is advertised using new LDP capability called as RMR capability
Must be advertised in the LDP Initialization message
If capability negotiations fails, RMR FEC element should not be advertised to the peer
LDP can set up regular LDP LSPs and RMR LSPs in a ring; however, an implementation may choose to enable only RMR LDP LSPs in the ring

4. RMR FEC Element
RMR FEC element is used to setup two counter rotating RMR LSPs in CW and AC direction for every node
Format
| RMR(TBD) | Address Family | PreLen |
| Ring Prefix |
~ ~
| |
| Ring ID |
| Ring Flags | Reserved |
Ring Flags value determine whether it is a CW or AC

5. Upstream LSR selection
During the discovery of a MPLS ring,
IGP populates its link state database
with ring information
After the discovery, there are just
two paths - one in clockwise direction
and other in anti-clockwise direction -
for every ring neighbor on a specific ring
A LDP transit and Egress LSR uses
This information to establish RMR
LSPs

6. LSP Procedures Egress LSR
Every ring node initiates two counter-rotating LSPs that egress on that node
Transit LSR
When a transit LSR receives Label mapping message with RMR FEC element, it should allocate a label, program a transit route and then select a upstream LSR as described earlier to send the label mapping message further upstream.
Ingress LSR
Every transit LSR is also a ingress LSR of a RMR LSP. The ingress LSR could either use CW or AC to reach the egress, or could use both CW and AC LSP to load balance the traffic to Egress. This decision is completely a local matter.

7. Protection
Protection happens naturally - No LFA, No R-LFA, No TI-LFA, No RSVP-TE Bypasses
RMR uses the two counter-rotating LSPs to protect one another

8. LSP Hierarchy
For simplicity, consider only RMR LSP setup inside the ring 17
Whenever services on N6 need to reach R12, N6 dynamically
establishes a tLDP session to ring 17 master node N1 and N10
Further, suppose N6 only learns IPv4 and IPv6 FECs
over this tldp sessions
In order to reach N12, N6 uses top label as RMR LSP label to
N1 and inner label as N12's FEC label received over
tLDP session to N1

9. Questions?