How to implement, test, debug and scale IPv4 Multicast in OpenStack.

2. Multicast in OpenStack
Internals, Limitations and Requirements for Media Workloads
Vikram Hosakote
Sr. Software Engineer, Cisco Systems
vhosakot@cisco.com
DEVNET-2055

3. • Multicast Concepts and Internals
• Multicast Use Cases
• Multicast in OpenStack
• Requirements and Limitations
• Multicast for Media Workloads
• Q & A
Agenda

4. Multicast Concepts and Internals

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What is multicast?
• One-to-many communication
• Packet duplication
• Driven by receivers
• A multicast “group” is identified by a multicast IP address
• Analogy: TV and radio broadcasting

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What is multicast?

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Lots of multicast RFCs!
• RFC 2236 Internet Group Management Protocol
• RFC 2365 Administratively Scoped IP Multicast
• RFC 2858 Multiprotocol Extensions for BGP-4
• RFC 3376 Internet Group Management Protocoll
• RFC 3446 Anycast Rendezvous Point (RP) mechanism using Protocol Independent Multicast (PIM) and Multicast Source Discovery Protocol
(MSDP)
• RFC 3569 An Overview of Source-Specific Multicast (SSM)
• RFC 3618 Multicast Source Discovery Protocol (MSDP)
• RFC 4291 IP Version 6 Addressing Architecture
• RFC 4541 Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches
• RFC 4601 Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)
• RFC 4610 Anycast-RP Using Protocol Independent Multicast (PIM)
• RFC 5059 Bootstrap Router (BSR) Mechanism for Protocol Independent Multicast (PIM)
• RFC 5132 IP Multicast MIB

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Network without multicast
• Sender must duplicate each packet
• Network congestion
• No group management
• Packet drop
• No difference between one-to-many and unicast communication

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Components of multicast
• Multicast addressing
• Multicast group management (IGMP)
• Multicast routing
• Multicast clients

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Components of multicast
• Multicast addressing
• Multicast group management (IGMP)
• Multicast routing
• Multicast clients

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Multicast addressing
• Multicast group addresses range from 224.0.0.0 to 239.255.255.255 (class D
addresses)
• Clients join or leave a multicast group address
• Multicast traffic is sent to all members of a group
• Multicast is unreliable (uses UDP)
• No Multicast with TCP!

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Multicast addressing
• First four bits of a class D address are 1110

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Multicast addressing – reserved addresses

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Multicast addressing – reserved addresses
• 224.0.0.1 All hosts on a subnet
• 224.0.0.2 All routers on a subnet
• 224.0.0.5 OSPF
• 224.0.0.6 OSPF DR
• 224.0.0.9 RIP
• 224.0.0.10 EIGRP
• 224.0.0.13 PIM
• 224.0.1.1 NTP

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Multicast addressing – layer-2 MAC address
• Mac addresses range from 01-00-5E-00-00-00 to 01-00-5E-7F-FF-FF
• The most significant 25 bits of the 48-bit mac address are fixed
• The lower 23 bits are variable and derived from the lower 23 bits of the multicast
IP address

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Components of multicast
• Multicast addressing
• Multicast group management (IGMP)
• Multicast routing
• Multicast clients

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Internet Group Management Protocol (IGMP)
• IGMP is used for group management of clients (receivers)
• Used by multicast routers to keep track of group membership
• Three versions – v1, v2, v3
• Receivers send IGMP reports (join and leave messages)
• Multicast routers send IGMP query messages to query group membership

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IGMP packet format

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IGMP snooping
• Network switch listens for IGMP messages and maintains a map of which links
need which IP multicast streams
• Prevents hosts on a local network from receiving traffic for a multicast group
they have not explicitly joined
• RFC 4541

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IGMP snooping

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Components of multicast
• Multicast addressing
• Multicast group management (IGMP)
• Multicast routing
• Multicast clients

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Multicast routing
• Multicast routing is done by layer-3 devices between the multicast source and
the receivers
• PIM (Protocol Independent Multicast)
• PIM Dense Mode (DM)
• PIM Sparse Mode (SM)
• PIM works with any unicast routing protocol
• EIGRP, OSPF, BGP, RIP, static routes

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Multicast routing – other protocols
• Distance Vector Multicast Routing Protocol (DVMRP)
• Multicast Open Shortest Path First (MOSPF)
• Core Based Tree (CBT)

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Multicast routing objectives
• Members should not receive duplicate multicast packets
• Non-members must not receive any multicast packets
• No routing loops
• Shortest best path from source to destination

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Multicast routing – PIM DM
• Push mechanism
• Flood-and-prune model
• Initially floods all multicast packets to all members
• Non-members send “prune” messages and do not receive packets over time
• Builds a source-based tree

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Multicast routing – PIM DM - join

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Multicast routing – PIM DM - flood

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Multicast routing – PIM DM - prune

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Multicast routing – PIM DM - routing

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Multicast routing – PIM DM - Cisco configuration
config terminal
ip multicast-routing
interface interface-id
ip pim dense-mode

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Multicast routing – PIM SM
• Pull mechanism
• Rendezvous Point (RP) is the meeting point for the senders and the receivers
• Receivers send IGMP join messages to RP
• Sender sends multicast packets to RP
• RP can be static or dynamic (Auto RP)
• Builds a shared-tree with RP

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Multicast routing – PIM SM - join

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Multicast routing – PIM SM - register and routing

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Multicast routing – PIM SM- Cisco configuration
config terminal
ip multicast-routing
ip pim rp-address <IP address of RP>
interface interface-id
ip pim sparse-mode

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Multicast routing – auto RP
• Cisco’s proprietary technology
• Used for dynamic RP election
• Primary and Secondary RP
• Reserved addresses:
• 224.0.1.39 The Cisco multicast router AUTO-RP-ANNOUNCE
• 224.0.1.40 The Cisco multicast router AUTO-RP-DISCOVERY

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Multicast routing – Reverse Path Forwarding (RPF)
• Unicast forwarding decision is based on the destination address
• Multicast forwarding decision is based on the source address found in the
reverse path (from the receiving router back to the source along the unicast best
path to the multicast source)

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Multicast routing – Reverse Path Forwarding (RPF)
• Without RPF check, R3
would forward packets
it got from R1 to R2,
R2 would forward
packets back to R1,
and R1 would forward
packets again to R3
• This creates routing
loops, and generates
multicast storms that
waste bandwidth and
router resources

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Components of multicast
• Multicast addressing
• Multicast group management (IGMP)
• Multicast routing
• Multicast clients

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Multicast clients
• Send IGMP join message
• Receive / consume multicast UDP traffic
• If clients / receivers are slower than the multicast source, packets are dropped
• Know that they receive unreliable traffic and do not expect retransmitted packets
• Send IGMP leave message (IGMP v2) when leaving a multicast group
• Respond to IGMP queries from upstream routers

40. Multicast Use Cases

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Multicast Use Cases
• One-to-many corporate communications such as:
• Employee training videos
• Quarterly company meetings
• Company-wide corporate communications
• Executive announcements
• Music / media streaming
• Video podcasts
• IPTV services

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Multicast Use Cases
• One-to-many software updates / patches
• Social networking (Facebook, Twitter feeds, Instagram)
• Financial services, banks, stock exchange
• Government / Federal agencies
• RTP (Real Time Protocol) applications

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Multicast Use Cases – Cisco’s Music on Hold (MoH)
• Music on hold (MoH) is
an integral feature of
the Cisco Unified
Communications
system
• This feature provides
music to callers when
their call is placed on
hold or transferred

44. Multicast in OpenStack

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Multicast in OpenStack – what is OpenStack?
• OpenStack is an open source cloud operating system that controls large pools
of compute, storage, and networking resources in a datacenter.
• Managed through a dashboard that gives administrators control to provision
resources through a web interface.

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Multicast in OpenStack
• No multicast available out-of-the-box
• Virtual layer-2 switches support IGMP snooping:
• Open vSwitch 2.5 supports IGMP snooping
• http://openvswitch.org/features/
• https://github.com/openvswitch/ovs/blob/master/FAQ.md
• Linux Bridge 2.4 supports IGMP snopping
• http://www.linuxfoundation.org/collaborate/workgroups/networking/bridge#Sn
ooping

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Multicast in OpenStack – virtual L-2 switch

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Multicast in OpenStack – virtual L-3 router
• Neutron is OpenStack’s networking-as-a-service
• Neutron-L3-Agent is OpenStack virtual layer-3 router
• Neutron-L3-Agent does not support multicast routing, PIM and querying
• No Neutron CLI or API to configure multicast routing
• Multicast routing cannot be configured in the OpenStack Horizon GUI

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Multicast in OpenStack – virtual L-3 router

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Multicast in OpenStack – recommendations
• Neutron provider network – Don’t use Neutron-L3-Agent (OpenStack’s virtual
router)
• Cisco’s ASR1k plugin for OpenStack Neutron instead of Neutron-L3-Agent
• Cisco’s ACI and APIC driver for Neutron

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Multicast in OpenStack – recommendations
• Neutron provider network:
• Don’t use Neutron-L3-Agent (OpenStack’s virtual router not used)
• Neutron does not route any multicast traffic
• Use Neutron provider network
• Use lab-routable public VLAN configured on top-of-rack switches
• Use lab router outside OpenStack
• Use lab gateway outside OpenStack
• Attach Nova instances directly to provider network
• Configure multicast routing / PIM on the lab router

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Multicast in OpenStack – provider network

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Multicast in OpenStack – provider network

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Multicast in OpenStack – recommendations
• Cisco’s ASR1k plugin for OpenStack Neutron :
• Neutron-L3-Agent (OpenStack’s virtual router) not used
• ASK1k plugin does both unicast and multicast routing
• Two ASR1000s used in VPC pair
• Neutron talks to ASR1k using Cisco’s config agent
• Neutron does not route any multicast traffic

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Multicast in OpenStack – Cisco’s ASR1k plugin

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Multicast in OpenStack – Cisco’s ASR1k plugin

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Multicast in OpenStack – Cisco’s ACI and APIC driver

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Multicast in OpenStack – UCSM multicast policy

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Multicast in OpenStack – UCSM multicast policy

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Multicast in OpenStack – ACI / APIC multicast policy

61. Requirements and Limitations

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Multicast requirements
• Multicast source
• UDP streams
• Multicast routing (PIM, RP, IGMP querier)
• Unicast routing (EIRGP, OSPF, BGP, RIP, etc)
• IGMP snooping
• No filters / ACLs that drop multicast traffic
• Multicast clients (IGMPv1, IGMPv2, IGMPv3)

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Multicast limitations
• IGMP snooping affects performance of the layer-2 switch as the switch must
read the destination IP address of each incoming packet
• High bandwidth multicast traffic affects performance of unicast routing
• Needs plugin (ASR1k, APIC) integration with OpenStack
• Best-effort delivery (UDP is unreliable)
• Out-of-sequence delivery
• Lack of TCP windowing results in network congestion
• Duplicate packets and occasional loops when unicast routing is broken

64. Multicast for Media Workloads

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Multicast for media applications
• Cisco Video conferencing – Telepresence, Webex, Jabber
• Cisco video and collaborations applications – Virtualized Video Processing
(V2P), Videoscape AnyRes, IPTV devices, video encoders, video surveillance,
etc
• VLC player
• http://www.videolan.org/projects/multicat.html
• https://wiki.videolan.org/Documentation:Streaming_HowTo/Advanced_streaming_with_samples,_mul
tiple_files_streaming,_using_multicast_in_streaming/
• https://wiki.videolan.org/Documentation:Streaming_HowTo/Receive_and_Save_a_Stream/

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Multicast tools
• Iperf - https://iperf.fr
• Nuttcp - http://www.nuttcp.net
• OpenStack VMTP - https://github.com/openstack/vmtp
• OpenStack Kloudbuster - https://github.com/openstack/kloudbuster

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References
• https://supportforums.cisco.com/document/128461/understanding-basics-multicast-rpf-reverse-path-forwarding
• http://www.slideshare.net/engineerrd/multicast-routing-protocols?qid=ed2afefe-3169-406d-a379-adcf491121d5&v=&b=&from_search=2
• http://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/nx-os/multicast/configuration/guide/b_multicast/b_multicast_chapter_0101.html
• http://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/1-
x/api/openstack/b_Cisco_APIC_OpenStack_Driver_Install_Guide/b_Cisco_APIC_OpenStack_Driver_Install_Guide_chapter_00.html
• https://ask.openstack.org/en/question/24679/can-we-launch-an-instance-that-behaves-as-a-router-in-openstack/
• http://superuser.openstack.org/articles/provisioning-neutron-networks-with-the-nsx-v-plugin
• http://blogs.cisco.com/cloud/openstack-asr1000-plugin-new-features
• http://blogs.cisco.com/datacenter/scaling-openstack-l3-using-cisco-asr1k-platform
• http://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/1-
x/api/openstack/b_Cisco_APIC_OpenStack_Driver_Install_Guide/b_Cisco_APIC_OpenStack_Driver_Install_Guide_chapter_00.html
• http://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/1-
x/virtualization/b_ACI_Virtualization_Guide/b_ACI_Virtualization_Guide_chapter_0100.html

68. Thank you

69. Please fill out survey and give feedback!

70. Q & A

72. Additional slides

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Multicast GLOP reserved addresses