DVMRP

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DVMRP

• Distance Vector Multicast Routing Protocol

Jerad Bates UMBC - Fall 2006
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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 internets multicast backbone
  (MBONE)

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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

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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

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DVMRP Packet
8 bits 8 bits 16 bits 16 bits
Type Code Checksum Checksum
Reserved Reserved Minor Version Major Version
Further portion of packet (up to 510 bytes) Depends on Code Further portion of packet (up to 510 bytes) Depends on Code Further portion of packet (up to 510 bytes) Depends on Code Further portion of packet (up to 510 bytes) Depends on Code

• Encapsulated in IP Datagrams (IP protocol number
  2, same as IGMP)
• IGMP Packet type of 0x13

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DVMRP Packet Structure
8 bits 8 bits 16 bits 16 bits
Type Code Checksum Checksum
Reserved Reserved Minor Version Major Version
Further portion of packet (up to 510 bytes) Depends on Code Further portion of packet (up to 510 bytes) Depends on Code Further portion of packet (up to 510 bytes) Depends on Code Further portion of packet (up to 510 bytes) Depends on Code

• Type Indicates packet is a DVMRP packet, set to
  0x13
• Code designates the type of DVMRP packet
• Checksum 1s compliment of the 1s complement of
  the entire packet (with checksum set to 0)
• Minor Major Versions Set to 0xFF and 3
  respectively for current version of DVMRP

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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

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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

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DVMRP Probe Packet
8 bits 8 bits 16 bits 16 bits
Type (0x13) Code (0x1) Checksum Checksum
Reserved Capabilities Minor Version Major Version
Generation ID Generation ID Generation ID Generation ID
Neighbor IP 1 Neighbor IP 1 Neighbor IP 1 Neighbor IP 1

Neighbor IP N Neighbor IP N Neighbor IP N Neighbor IP N
Generation ID Used to identify changes in router
state
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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

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DVMRP Report Packet
8 bits 8 bits 16 bits 16 bits
Type (0x13) Code (0x2) Checksum Checksum
Reserved Reserved Minor Version Major Version
Mask 1 (Oct 2) Mask 1 (Oct 3) Mask 1 (Oct 4) Src Net 11
Src Net 11 Src Net 11 Metric 11 Src Net 12
Src Net 12 Src Net 12 Metric 12
Mask 2 (Oct 2)
Mask 2 (Oct 3) Mask 2 (Oct 4) Src Net 21 Src Net 21
Src Net 21 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.
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DVMRP Ask Neighbors 2

• Unicast message sent to a specific neighboring
  router
• Asks neighbor to respond with a list of its
  neighbors

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DVMRP Ask Neighbors 2 Packet
8 bits 8 bits 16 bits 16 bits
Type (0x13) Code (0x5) Checksum Checksum
Reserved Reserved Minor Version Major Version
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DVMRP Neighbors 2

• Response to Ask Neighbors 2 message
• Contains a list of the routers interfaces and
  addresses of routers attached to those interfaces

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DVMRP Neighbors 2 Packet
8 bits 8 bits 8 bits 16 bits 16 bits
Type (0x13) Type (0x13) Code (0x6) Checksum Checksum
Reserved Reserved Capabilities Minor Version Major Version
Local Address 1 Local Address 1 Local Address 1 Local Address 1 Local Address 1
Metric 1 Threshold 1 Threshold 1 Flags 1 Number Count 1
Number 1 Number 1 Number 1 Number 1 Number 1

Number M Number M Number M Number M Number M

Local Address N Local Address N Local Address N Local Address N Local Address N
Metric N Threshold N Threshold N Flags N Number Count N
Number 1 Number 1 Number 1 Number 1 Number 1

Number K Number K Number K Number K Number K
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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

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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

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DVMRP Prune Packet
8 bits 8 bits 16 bits 16 bits
Type (0x13) Code (0x7) Checksum Checksum
Reserved Reserved Minor Version Major Version
Source Host Address Source Host Address Source Host Address Source Host Address
Group Address Group Address Group Address Group Address
Prune Lifetime Prune Lifetime Prune Lifetime Prune Lifetime
Source Network Mask (optional) Source Network Mask (optional) Source Network Mask (optional) 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
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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

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DVMRP Graft Packet
8 bits 8 bits 16 bits 16 bits
Type (0x13) Code (0x8) Checksum Checksum
Reserved Reserved Minor Version Major Version
Source Host Address Source Host Address Source Host Address Source Host Address
Group Address Group Address Group Address Group Address
Source Network Mask (optional) Source Network Mask (optional) Source Network Mask (optional) 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
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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

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DVMRP Graft Ack Packet
8 bits 8 bits 16 bits 16 bits
Type (0x13) Code (0x9) Checksum Checksum
Reserved Reserved Minor Version Major Version
Source Host Address Source Host Address Source Host Address Source Host Address
Group Address Group Address Group Address Group Address
Source Network Mask (optional) Source Network Mask (optional) Source Network Mask (optional) 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
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DVMRP Issues

• DVMRP is based on RIP and carries over many of
  RIPs 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

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Sources

• Original RFC RFC 1075 http//tools.ietf.org/html/
  rfc1075
• Latest Draft http//www.ietf.org/internet-drafts/
  draft-ietf-idmr-dvmrp-v3-11.txt
• http//www.ncne.org/documentation/faq/mcast_eng_fa
  q.html