Stateless Multicast with Bit Indexed Explicit Replication (BIER)

Transcription

1 Stateless Multicast with it Indexed Explicit Replication (IER) Alvaro Retana Distinguished Engineer, Cisco Services Slides by: IJsbrand Wijnands

2 it Indexed Explicit Replication (IER) Only encode the end-receivers in the packet header. Not the intermediate nodes. Assign end-receivers a it Position from a it String. The smallest identifier possible. Encode the it String in the packet header. Using some sort of encapsulation. Create a it Forwarding Table on all IER nodes to allow multicast packet forwarding using the it String in the packet. Derived from the RI, SPF based. 2

3 IETF The IER idea was presented in a OF at the IETF in Hawaii. November A new IER Working Group has been formed (bier@ietf.org) draft-ietf-bier-problem-statement-00 draft-ietf-bier-architecture-00 draft-ietf-bier-encapsulation-mpls-00 draft-ietf-bier-use-cases-00 draft-ietf-l3vpn-mvpn-bier-00 draft-ietf-ospf-bier-extensions-00 draft-przygienda-bier-isis-ranges-01 draft-eckert-bier-te-arch-00 draft-xu-idr-bier-extensions-00 3

4 Solution Overview 4

5 asic Idea IER A/32 /32 LSA 2 /32 LSA 3 C/32 LSA 1 - A/32 IER Domain LSA 4 D/32 LSA 5 E/32 E/ itstring C/32 D/32 1. Assign a unique it Position from a itstring to each FER in the IER domain. 2. Each FER floods their it Position to FR-prefix mapping using the IGP (OSPF, ISIS) 5

6 asic Idea IER A/32 /32 E/32 itmask A C C/32 D/32 1. Assign a unique it Position from a itstring to each FER in the IER domain. 2. Each FER floods their it Position to FR-prefix mapping using the IGP (OSPF, ISIS) 6

7 it Index Forwarding Table M M M C 0100 E D 0010 F D M-ER A C M 0011 C E 0100 M-ER F 0010 M-ER D, F and E advertise their it positions in the IGP (flooded). ased on shortest path route to RID, the it Mask Forwarding Table is created 7

8 Forwarding Packets M M M 0111 A & C &0011 D & 0100 E 0010 F C D 0011 C E 0100 F

9 Forwarding Packets & C &0011 D & 0100 E & F A 0101 C D C E 0100 F

10 Forwarding Packets & C &0011 D & 0100 E & F &0010 A C D E F C 10

11 ECMP Duplicate bit positions need to be resolved, ECMP logic needs to select based on Hash. In the example we selected C A & C &0011 D & 0110 E & F & C D E 0100 F C 0010 F 11

12 MPLS encapsulation We ve analyzed the MPLS option, CRS and ASR9K platform. oth these platforms can do 256 bits. We consider 256 a good starting point. Other vendors confirmed they can do 256. IER Label IER Header VPN Label Payload EOS EOS MPLS Label IER header Upstream Label (optional) IPv4/IPv6/L2 12

13 IER Header 256bits = 32bytes Ver Len Entropy itstring (first 32 bits) ~ ~ ~ ~ itstring (last 32 bits) OAM Reserved Proto FIR-id

14 Sets and Areas 14

15 IER Sets A 1: Set M I G 1:0010 Set I J 1:0111 2:0111 Note, we create different forwarding entries for each Set I Note, it Positions 1,2,3 appear in both Sets, and do not overlap due to Sets. H C D E 1:0100 2: 2:0010 Set 2 To increase the scale we group the egress routers in Sets. F 2:

16 IER Sets Set M I G A 1: Set 1 1: I J 1:0111 2:0111 I Set 2 C 2: Note, we create different forwarding entries for each Set There is no topological restriction which set an egress belongs to H Set 1 D E F 1:0100 2:0010 Set 2 2:

17 IER Area M M M M 0:10 AR 0:01 A 0:01 0:10 AR Area 1 Area 2 A AR {0:01} {0:10} {0:10} {0:01} A bit Mask only needs to be unique in its own area. AR s translate it Masks between area s. Requires a IP lookup and state on the ARs. This is very similar for Segmented Inter-AS MVPN. 17

18 Native IER 18

19 Native IER With Native IER there is NO PIM involved, just IGMP and IER. The Source and Receiver(s) are connected to IER router. There are no RP s. There is no equivalent of PIM modes, like sparse, ssm, bidir etc.. We speak of single sender and multi sender, which is basically the same solution. The overlay can be GP or SDN based. 19

20 Native IER (S1,G) A 0100 (*,G):0: E IGMP (*,G) C C D D D 0100 A 1000 E 0010 F 1100 C (*,G):0:0010 F 0010 IGMP (*,G) C 1101 D E and F announce their Group membership via overlay to all other routers. A IER router connected to the Source can immediately start sending. 20

21 Native IER (S1,G) (*,G):0:0010 (*,G):0: A 0100 (*,G):0:0010 E IGMP (*,G) C C D D (S2,G) (*,G):0:0010 (*,G):0: D 0100 A E 0010 F 1100 C (*,G):0: F 0010 IGMP (*,G) C 1101 D When leans about a new source, it can immediately start sending. 21

22 MVPN over IER 22

23 MVPN over IER IER replaces PIM, mldp, RSVP-TE or IR in the core. IER represents a full mesh (P2MP) connectivity between all the PE s in the network. There is no need to explicitly signal any MDT s (or PMSI s). With MVPN there are many profiles, This is partly due to the tradeoff between State and Flooding. Different C-multicast signaling options. MVPN over IER, there is one profile. GP for C-multicast signaling. No need for Data-MDTs. 23

24 MVPN over IER (S,G) PIM (*,G):0: (*,G):0:0010 (*,G):0: RR PIM (*,G) (S1,G) PIM A 0100 C PIM (*,G) IER (*,G):0: (S2,G) PIM D PIM (*,G) The GP control plane defined for MVPN can be re-used. ig difference, there is no Tree per VPN!!! The IER packets needs to carry Source ID and upstream VPN context label 24

25 Conclusion 25

26 Advantages Packets forwarded via IER follow the unicast path towards the receiver, inheriting unicast features like FRR and LFA. There is no per multicast flow state in the network. Multicast convergence is as fast as unicast, there is no multicast state to re-converge, signal, etc. Nice plugin for SDN, its only the ingress and egress that need to exchange Sender and Receiver information. The core network provides a many-2-many connectively between all IER routers by default following the IGP. No Multicast control protocol in the network. Goes hand in hand with Segment Routing 26

27 Disadvantages The it String length has an upper bound and may not cover all deployment scenarios. Using sets to increase the number of egress routers may cause the ingress to replicate the packet multiple times. Using area s requires the AR to have state. 27

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