This document describes a 5 seconds delay in forwarding multicast traffic over the Multipoint Label Distribution Protocol (mLDP) tree when a Remote Receiver joins the multicast Group and when the ingress PE router runs Cisco IOS® XR.
A Remote Receiver is a Receiver across the mLDP backbone from the point of view of the Source.
The 5 seconds delay was introduced on purpose due to CSCvb50266 5 Seconds MLDP forwarding delay to local receiver when there is an existing MVPN receiver
This CDETS was created to work around the issue of CSCtg68851 Switchover from default to Data MDTs is not hitless for LC multipath
If the ingress PE router runs an IOS®-XR version after CSCtg68851, the 5 second delay will be there.
If the ingress PE router runs an IOS®-XR version after CSCvb50266, the 5 second delay will be there by default.
If this is not wanted, the forwarding of the multicast stream can be speed up by a hidden configuration command.
Here is an example.
Look at Figure 1 for a test topology.
CE1 is the Source 10.100.1.5 for the multicast stream 184.108.40.206.
CE2 and CE1-B are the receivers for the multicast stream 220.127.116.11.
Test 1. Remote Receiver Joins with No Local Receiver
RP/0/0/CPU0:PE1#debug mrib vrf one route RP/0/0/CPU0:PE1#debug mfib vrf one ipv4 encap RP/0/0/CPU0:PE1#show debug
#### debug flags set from tty 'con0_0_CPU0' #### ipv4 mfwd encap flag is ON with value '0x1##one' ipv4 mrib route flag is ON with value 'one#'
There is no local receiver on the ingress PE router PE1:
RP/0/0/CPU0:PE1#sh mrib vrf one route 18.104.22.168 10.100.1.5 No matching route in MRIB route-DB RP/0/0/CPU0:PE1#
The encap-ID is set to 7, 5 seconds after the encap-ID was created and the Multicast Routing Information Base (MRIB) was updated with the Labeled MDT (LMDT) interface for Virtual Routing and Forwarding (VRF) one in the Outgoing Interface List (OIL).
RP/0/0/CPU0:PE1#show mrib vrf one route 22.214.171.124 10.100.1.5
IP Multicast Routing Information Base Entry flags: L - Domain-Local Source, E - External Source to the Domain, C - Directly-Connected Check, S - Signal, IA - Inherit Accept, IF - Inherit From, D - Drop, ME - MDT Encap, EID - Encap ID, MD - MDT Decap, MT - MDT Threshold Crossed, MH - MDT interface handle CD - Conditional Decap, MPLS - MPLS Decap, EX - Extranet MoFE - MoFRR Enabled, MoFS - MoFRR State, MoFP - MoFRR Primary MoFB - MoFRR Backup, RPFID - RPF ID Set, X - VXLAN Interface flags: F - Forward, A - Accept, IC - Internal Copy, NS - Negate Signal, DP - Don't Preserve, SP - Signal Present, II - Internal Interest, ID - Internal Disinterest, LI - Local Interest, LD - Local Disinterest, DI - Decapsulation Interface EI - Encapsulation Interface, MI - MDT Interface, LVIF - MPLS Encap, EX - Extranet, A2 - Secondary Accept, MT - MDT Threshold Crossed, MA - Data MDT Assigned, LMI - mLDP MDT Interface, TMI - P2MP-TE MDT Interface IRMI - IR MDT Interface
(10.100.1.5,126.96.36.199) RPF nbr: 10.2.1.5 Flags: RPF Up: 01:04:11 Incoming Interface List GigabitEthernet0/0/0/0 Flags: A, Up: 01:04:11 Outgoing Interface List Lmdtone Flags: F LMI MA TR, Up: 00:03:33 GigabitEthernet0/0/0/2 Flags: F NS, Up: 01:04:11
RP/0/0/CPU0:PE1#show mfib vrf one route 188.8.131.52 10.100.1.5 detail
IP Multicast Forwarding Information Base Entry flags: C - Directly-Connected Check, S - Signal, D - Drop, IA - Inherit Accept, IF - Inherit From, EID - Encap ID, ME - MDT Encap, MD - MDT Decap, MT - MDT Threshold Crossed, MH - MDT interface handle, CD - Conditional Decap, DT - MDT Decap True, EX - Extranet, RPFID - RPF ID Set, MoFE - MoFRR Enabled, MoFS - MoFRR State, X - VXLAN Interface flags: F - Forward, A - Accept, IC - Internal Copy, NS - Negate Signal, DP - Don't Preserve, SP - Signal Present, EG - Egress, EI - Encapsulation Interface, MI - MDT Interface, EX - Extranet, A2 - Secondary Accept Forwarding/Replication Counts: Packets in/Packets out/Bytes out Failure Counts: RPF / TTL / Empty Olist / Encap RL / Other
So, the remote receiver has an extra delay of 5 seconds in receiving this multicast stream.
Note: The LMDT interface got added in the MRIB immediately and that the LMDT interface also got added in the MFIB immediately with the F flag, but with the encap ID not set.
The encap ID in the MFIB got set after the 5 seconds delay.
After CSCvb50266, the delay is 5 seconds for the programming of the encap-ID when a remote receiver joins. This is the new default behavior.
Run the command show pim vrf <> context in order to verify the behavior:
RP/0/0/CPU0:PE1#show pim vrf one context
PIM context information for VRF one (0x12b70184)
VRF ID: 0x60000001 Table ID: 0xe0000010 Remote Table ID: 0xe0800010 MDT Default Group : 0.0.0.0 MDT Source : (10.100.1.1, Loopback0) Per-VRF MDT Immediate Switch Not Configured MDT handle: 0x0(Null) Context Active, ITAL Active Routing Enabled Registered with MRIB Not owner of MDT Interface Raw socket req: T, act: T, LPTS filter req: T, act: T UDP socket req: T, act: T, UDP vbind req: T, act: T Reg Inj socket req: T, act: T, Reg Inj LPTS filter req: T, act: T Mhost Default Interface : GigabitEthernet0/0/0/0 (publish pending: F) Remote MDT Default Group : 0.0.0.0 Backup MLC virtual interface: Null Neighbor-filter: - MDT Neighbor-filter: -
Run this hidden command mdt immediate-switch in order to remove the delay of 5 seconds.
RP/0/0/CPU0:PE1#conf t RP/0/0/CPU0:PE1(config)#multicast-routing vrf one RP/0/0/CPU0:PE1(config-mcast-one)#address-family ipv4 RP/0/0/CPU0:PE1(config-mcast-one-ipv4)#mdt immediate-switch RP/0/0/CPU0:PE1(config-mcast-one-ipv4)#commit