1. DVMRP Distance Vector Multicast Routing Protocol Jerad Bates UMBC - Fall 2006

2. DVMRP Basics An interior gateway protocol Functions within an Autonomous System (AS) but not between ASs Can only route multicast datagrams Routers need additional protocol(s) for non- multicast routing, but DVMRP could be extended to unicast Basis for the internet’s multicast backbone (MBONE)

3. How DVMRP Fits Into Multicasting IGMP - used for discovery of hosts in multicast groups, messages exchanged between neighbors DVMRP - routes multicast datagrams within an AS MBGP (Multicast BGP) - routes multicast datagrams between ASs

4. DVMRP Tree Spanning and Pruning Uses Reverse Path Flooding to forward multicast data Uses Pruning to reduce amount of traffic needed to be sent Pruning occurs when routers receive multicast data for which they have no paths that subscribe to that group Routers then send back pruning packets to tell the sending router not to send it packets for that multicast group

5. DVMRP Packet Encapsulated in IP Datagrams (IP protocol number 2, same as IGMP) IGMP Packet type of 0x13 8 bits 16 bits TypeCodeChecksum ReservedMinor VersionMajor Version Further portion of packet (up to 510 bytes) – Depends on Code

6. DVMRP Packet Structure Type: Indicates packet is a DVMRP packet, set to 0x13 Code: designates the type of DVMRP packet Checksum: 1’s compliment of the 1’s complement of the entire packet (with checksum set to 0) Minor & Major Versions: Set to 0xFF and 3 respectively for current version of DVMRP 8 bits 16 bits TypeCodeChecksum ReservedMinor VersionMajor Version Further portion of packet (up to 510 bytes) – Depends on Code

7. DVMRP Codes 7 Types of Codes 1 – Probe: Neighbor discovery 2 – Report: Route exchange 5 – Ask Neighbors 2: Request neighbor list 6 – Neighbors 2: Respond with neighbor list 7 – Prune: Pruning delivery trees 8 – Graft: Grafting delivery trees 9 – Graft Ack: Acknowledge graft messages Note: 3 & 4 are obsolete versions of 5 & 6

8. DVMRP Probe Sent out on every interface 3 Purposes Finds neighbors Alerts neighbors of routers presence and capabilities Helps detect neighbor loss, sent ever 10sec, timeout if not received in 35 Contains a list of Neighbors, allows neighbors to know they have been detected

9. DVMRP Probe Packet 8 bits 16 bits Type (0x13)Code (0x1)Checksum ReservedCapabilitiesMinor VersionMajor Version Generation ID Neighbor IP 1 …… Neighbor IP N Generation ID: Used to identify changes in router state

10. DVMRP Report Used to find neighbor to route traffic back to sender through Uses hop count as the metric Contains a list of source networks and metrics

11. DVMRP Report Packet 8 bits 16 bits Type (0x13)Code (0x2)Checksum ReservedMinor VersionMajor Version Mask 1 (Oct 2)Mask 1 (Oct 3)Mask 1 (Oct 4)Src Net 11 Metric 11Src Net 12 Metric 12… ……Mask 2 (Oct 2) Mask 2 (Oct 3)Mask 2 (Oct 4)Src Net 21 Metric 21… … Sources are paired with masks, can have more then one source paired with a mask. Lists all sources a router has contact with and the cost of that route.

12. DVMRP Ask Neighbors 2 Unicast message sent to a specific neighboring router Asks neighbor to respond with a list of its neighbors

13. DVMRP Ask Neighbors 2 Packet 8 bits 16 bits Type (0x13)Code (0x5)Checksum ReservedMinor VersionMajor Version

14. DVMRP Neighbors 2 Response to Ask Neighbors 2 message Contains a list of the router’s interfaces and addresses of routers attached to those interfaces

15. DVMRP Neighbors 2 Packet 8 bits 16 bits Type (0x13)Code (0x6)Checksum ReservedCapabilitiesMinor VersionMajor Version Local Address 1 Metric 1Threshold 1Flags 1Number Count 1 Number 1 … Number M …… Local Address N Metric NThreshold NFlags NNumber Count N Number 1 … Number K

16. DVMRP Neighbors 2 Packet (continued) Local Addresses exist for each interface on the router Following that are characteristics of that interface The Number X fields contain all the routers that are neighbors of that port

17. DVMRP Prune Sent from routers receiving multicast traffic for which they have no downstream group members “Prunes” the tree created by DVMRP Stops needless data from being sent

18. DVMRP Prune Packet 8 bits 16 bits Type (0x13)Code (0x7)Checksum ReservedMinor VersionMajor Version Source Host Address Group Address Prune Lifetime Source Network Mask (optional) Source Host IP Address: Address of device that sent the prune request Group Address: Multicast group address that is requested to be pruned Prune Lifetime: Length of time, in seconds (up to ~2hrs), to keep branch pruned Source Network Mask: The netmask of the route the pruning applies to

19. DVMRP Graft Used after a branch has been pruned back Sent upstream by a router that has a host that joins a multicast group Goes from router to router until a router active on the multicast group is reached Sent for the following cases A new host member joins a group A new dependent router joins a pruned branch A dependent router restarts on a pruned branch If a Graft Ack is not received before the timeout

20. DVMRP Graft Packet 8 bits 16 bits Type (0x13)Code (0x8)Checksum ReservedMinor VersionMajor Version Source Host Address Group Address Source Network Mask (optional) Source Host IP Address: Address of router or network to graft Group Address: Multicast group address that is requested to be grafted Source Network Mask: The netmask of the route the grafting applies to

21. DVMRP Graft Ack Used to acknowledge receipt of Graft message Allows sending downstream router to know upstream router has received and processed its request If not received within 5 sec. Graft message sent again

22. DVMRP Graft Ack Packet 8 bits 16 bits Type (0x13)Code (0x9)Checksum ReservedMinor VersionMajor Version Source Host Address Group Address Source Network Mask (optional) Source Host IP Address: Address of router or network that was received in request Group Address: Multicast group address that was received in request Source Network Mask: The netmask of the route the Graft Ack covers

23. DVMRP Issues DVMRP is based on RIP and carries over many of RIP’s issues Hop count used as metric Scalability issues Performs periodic flooding Maintains its own routing table Older versions lack pruning Even though it is a main part of MBONE, MBONE is being phased out

24. Sources Original RFC: RFC 1075 http://tools.ietf.org/html/rfc1075 http://tools.ietf.org/html/rfc1075 Latest Draft: http://www.ietf.org/internet- drafts/draft-ietf-idmr-dvmrp-v3-11.txt http://www.ietf.org/internet- drafts/draft-ietf-idmr-dvmrp-v3-11.txt http://www.ncne.org/documentation/fa q/mcast_eng_faq.html