HP 5500 Ei 5500 Si Switch Series Configuration Guide
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5 Multicast models Based on how the receivers treat the multicast sources, the multicast models include any-source multicast (ASM), source-filtered multicast (SFM), and source-specific multicast (SSM). ASM model In the ASM model, any sender can send information to a multicast group as a multicast source, and receivers can join a multicast group (identified by a group address) and obtain multicast information addressed to that multicast group. In this model, receivers do not know the positions of the multicast sources in advance. However, they can join or leave the multicast group at any time. SFM model The SFM model is derived from the ASM model. To a sender, the two models appear to have the same multicast membership architecture. The SFM model functionally extends the ASM model. The upper-layer software checks the source address of received multicast packets and permits or denies multicast traffic from specific sources. Therefore, receivers can receive the multicast data from only part of the multicast sources. To a receiver, multicast sources are not all valid; they are filtered. SSM model Users might be interested in the multicast data fr om only certain multicast sources. The SSM model provides a transmission service that enables users to specify the multicast sources that they are interested in at the client side. The main difference between the SSM model and the ASM model is that in the SSM model, receivers have already determined the locations of the multicast sources by some other means. In addition, the SSM model uses a multicast address range that is different from that of the ASM/SFM model, and dedicated multicast forwarding paths are establis hed between receivers and the specified multicast sources. Multicast architecture IP multicast addresses the following questions: • Where should the multicast source transmit information to? (multicast addressing) • What receivers exist on the network? (host registration) • Where is the multicast source that will provide data to the receivers? (multicast source discovery) • How should information be transmitted to the receivers? (multicast routing) IP multicast is an end-to-end service. The multicast architecture involves the following parts: • Addressing mechanism —A multicast source sends information to a group of receivers through a multicast address. • Host registration —Receiver hosts can join and leave multicast groups dynamically. This mechanism is the basis for management of group memberships. • Multicast routing —A multicast distribution tree (namely, a forwarding path tree for multicast data on the network) is constructed for delivering multicast data from a multicast source to receivers. • Multicast applications —A software system that supports multicast applications, such as video conferencing, must be installed on multicast sour ces and receiver hosts. The TCP/IP stack must support reception and transmission of multicast data.
6 Multicast addresses Network-layer multicast addresses (multicast IP addresses) enables communication between multicast sources and multicast group members. In addition, a technique must be available to map multicast IP addresses to link-layer multicast MAC addresses. IP multicast addresses • IPv4 multicast addresses Internet Assigned Numbers Authority (IANA) a ssigned the Class D address space (224.0.0.0 to 239.255.255.255) to IPv4 multicast. Table 2 Class D IP address blocks and description Address block Descri ption 224.0.0.0 to 224.0.0.255 Reserved permanent group addresses. The IP address 224.0.0.0 is reserved. Other IP addresses can be used by routing protocols and for topology searching, protocol maintenance, and so on. Table 3 li sts common permanent group addresses. A packet destined for an address in this block will not be forwarded beyond the local subnet regardless of the Time to Live (TTL) value in the IP header. 224.0.1.0 to 238.255.255.255 Globally scoped group addresses. This block includes the following types of designated group addresses: • 232.0.0.0/8 —SSM group addresses, and • 233.0.0.0/8 —Glop group addresses. 239.0.0.0 to 239.255.255.255 Administratively scoped multicas t addresses. These addresses are considered locally unique rather than globally unique, and can be reused in domains administered by different organizations without causing conflicts. For more information, see RFC 2365. NOTE: Glop is a mechanism for assi gning multicast addresses between different autonomous systems (ASs). By fillin g an AS number into the middle two bytes of 233.0.0.0, you get 255 multicast addresses for that AS. For more information, see RFC 2770. Table 3 Some reserved multicast addresses Address Descri ption 224.0.0.1 All systems on this subnet, including hosts and routers 224.0.0.2 All multicast routers on this subnet 224.0.0.3 Unassigned 224.0.0.4 Distance Vector Multicast Routing Protocol (DVMRP) routers 224.0.0.5 Open Shortest Path First (OSPF) routers 224.0.0.6 OSPF designated routers and backup designated routers 224.0.0.7 Shared Tree (ST) routers 224.0.0.8 ST hosts 224.0.0.9 Routing Information Protocol version 2 (RIPv2) routers 224.0.0.11 Mobile agents
7
Address Description
224.0.0.12 Dynamic Host Configuration Protocol (DHCP) server/relay agent
224.0.0.13 All Protocol Independent Multicast (PIM) routers
224.0.0.14 Resource Reservation Protocol (RSVP) encapsulation
224.0.0.15 All Core-Based Tree (CBT) routers
224.0.0.16 Designated Subnetwork Bandwidth Management (SBM)
224.0.0.17 All SBMs
224.0.0.18 Virtual Router Redundancy Protocol (VRRP)
• IPv6 multicast addresses
Figure 4 IPv6 multicast format
The following describes the fields of an IPv6 multicast address:
{ 0xFF—The most significant eight bits are 1 1111111, which indicates that this address is an IPv6
multicast address.
{ Flags —The Flags field contains four bits.
Figure 5 Flags field format
Table 4 Flags field description
Bit Descri
ption
0 Reserved, set to 0
R
• When set to 0, it indicates that this address is an IPv6 multicast
address without an embedded RP address
• When set to 1, it indicates that this address is an IPv6 multicast
address with an embedded RP address (the P and T bits must
also be set to 1)
P
• When set to 0, it indicates that this address is an IPv6 multicast
address not based on a unicast prefix
• When set to 1, it indicates that this address is an IPv6 multicast
address based on a unicast prefix (the T bit must also be set to 1)
T
• When set to 0, it indicates that this address is an IPv6 multicast
address permanently-assigned by IANA
• When set to 1, it indicates that this address is a transient, or
dynamically assigned IPv6 multicast address
8
{ Scope —The Scope field contains four bits, which indicate the scope of the IPv6 internetwork for
which the multicast traffic is intended.
Table 5 Values of the Scope field
Value Meanin
g
0, F Reserved
1 Interface-local scope
2 Link-local scope
3 Subnet-local scope
4 Admin-local scope
5 Site-local scope
6, 7, 9 through D Unassigned
8 Organization-local scope
E Global scope
{
Group ID —The Group ID field contains 1 12 b i t s . I t u n i q u e l y i d e n t i fi e s a n I P v 6 m u l t i c a s t g ro u p i n
the scope that the Scope field defines.
Ethernet multicast MAC addresses
A multicast MAC address identifies a group of receivers at the data link layer.
• IPv4 multicast MAC addresses
As defined by IANA, the most si gnificant 24 bits of an IPv4 multicast MAC address are 0x01005E.
Bit 25 is 0, and the other 23 bits are the least significant 23 bits of a multicast IPv4 address.
Figure 6 IPv4-to-MAC address mapping
The most significant four bits of a multicast IPv4 address are 1110, which indicates that this
address is a multicast address. Only 23 bits of the remaining 28 bits are mapped to a MAC
address, so five bits of the multicast IPv4 address are lost. As a result, 32 multicast IPv4 addresses
map to the same IPv4 multicast MAC address. Therefore, in Layer 2 multicast forwarding, a switch
might receive some multicast data destined for ot her IPv4 multicast groups. The upper layer must
filter such redundant data.
• IPv6 multicast MAC addresses
The most significant 16 bits of an IPv6 mult icast MAC address are 0x3333. The least significant
32 bits are the least significant 32 bits of a multicast IPv6 address.
9 Figure 7 An example of IPv6-to-MAC address mapping Multicast protocols Generally, Layer 3 multicast refers to IP multicast working at the network layer. The corresponding multicast protocols are Layer 3 multicast protocols, which include IGMP, MLD, PIM, IPv6 PIM, MSDP, MBGP, and IPv6 MBGP. Layer 2 multicast refers to IP multicast working at the data link layer. The corresponding multicast protocols are Layer 2 multicast protocols, which include IGMP snooping, MLD snooping, PIM snooping, IPv6 PIM snooping, multicast VLAN, and IPv6 multicast VLAN. IGMP snooping, PIM snooping, multicast VLAN, IGMP, PIM, MSDP, and MBGP are for IPv4, and MLD snooping, IPv6 PIM snooping, IPv6 multicast VLAN, MLD, IPv6 PIM, and IPv6 MBGP are for IPv6. This section provides only general descriptions about applications and functions of the Layer 2 and Layer 3 multicast protocols in a network. For more information about these protocols, see the related chapters. Layer 3 multicast protocols Layer 3 multicast protocols include multicast group management protocols and multicast routing protocols. Figure 8 Positions of Layer 3 multicast protocols • Multicast group management protocols Typically, the Internet Group Management Protocol (IGMP) or Multicast Listener Discovery Protocol (MLD) is used between hosts and Layer 3 multicast de vices that directly connect to the hosts. These
10
protocols define the mechanism of establishing and maintaining group memberships between
hosts and Layer 3 multicast devices.
• Multicast routing protocols
A multicast routing protocol runs on Layer 3 mult icast devices to establish and maintain multicast
routes and forward multicast packets correctly and ef ficiently. Multicast routes constitute loop-free
data transmission paths from a data source to mult iple receivers, namely, a multicast distribution
tree.
In the ASM model, multicast routes include in tra-domain routes and inter-domain routes.
{ An intra-domain multicast routing protocol di scovers multicast sources and builds multicast
distribution trees within an AS to deliver multicast data to receivers. Among a variety of mature
intra-domain multicast routing protocols, Protoc ol Independent Multicast (PIM) is most widely
used. Based on the forwarding mechanism, PIM has dense mode (often referred to as
PIM-DM), and sparse mode (often referred to as PIM-SM).
{ An inter-domain multicast routing protocol is used for delivery of multicast information between
two ASs. So far, mature solutions include Multicast Source Discovery Protocol (MSDP) and
Multicast Border Gateway Protocol (MBGP). MS DP propagates multicast source information
among different ASs. MBGP is an extension of the Multiprotocol Border Gateway Protocol
(MP-BGP) for exchanging multicast routing information among different ASs.
For the SSM model, multicast routes are not divi ded into intra-domain routes and inter-domain
routes. Because receivers know the position of the multicast source, channe ls established through
PIM-SM are sufficient for the tran sport of multicast information.
Layer 2 multicast protocols
Layer 2 multicast protocols include IGMP snooping, MLD snooping, PIM snooping, IPv6 PIM snooping,
multicast VLAN, and IPv6 multicast VLAN.
Figure 9 Positions of Layer 2 multicast protocols
• IGMP snooping and MLD snooping
IGMP snooping and MLD snooping are multicast co nstraining mechanisms that run on Layer 2
devices. They manage and control multicast grou ps by monitoring and analyzing IGMP or MLD
messages exchanged between the hosts and Layer 3 multicast devices, effectively controlling the
flooding of multicast data in a Layer 2 network.
11 • PIM snooping and IPv6 PIM snooping PIM snooping and IPv6 PIM snooping run on Laye r 2 devices. They determine which ports are interested in multicast data by analyzing the re ceived IPv6 PIM messages, and add the ports to a multicast forwarding entry to make sure that multicast data can be forwarded to only the ports that are interested in the data. • Multicast VLAN and IPv6 multicast VLAN In the traditional multicast-on-demand mode, when users in different VLANs on a Layer 2 device need multicast information, the upstream Layer 3 device must forward a separate copy of the multicast data to each VLAN of the Layer 2 devi ce. When the multicast VLAN or IPv6 multicast VLAN feature is enabled on the Layer 2 device, th e Layer 3 multicast device sends only one copy of multicast to the multicast VLAN or IPv6 mult icast VLAN on the Layer 2 device. This approach avoids waste of network bandwidth and extra burden on the Layer 3 device. Multicast packet forwarding mechanism In a multicast model, a multicast source sends information to the host group identified by the multicast group address in the destination address field of IP multicast packets. To deliver multicast packets to receivers located at different positions of the networ k, multicast routers on the forwarding paths usually need to forward multicast packets that an incoming interface receives to multiple outgoing interfaces. Compared with a unicast model, a multicast model is more complex in the following aspects: • To ensure multicast packet transmission in the network, unicast routing tables or multicast routing tables (for example, the MBGP routing table) specially provided for multicast must be used as guidance for multicast forwarding. • To process the same multicast information from different peers received on different interfaces of the same device, every multicast packet undergoes a reverse path forwarding (RPF) check on the incoming interface. The result of the RPF check de termines whether the packet will be forwarded or discarded. The RPF check mechanism is the basis for most multicast routing protocols to implement multicast forwarding. For more information about the RPF mechanism, see Configuring multicast routing and forwarding ( available only on the HP 5500 EI) and Configuring IPv6 multicast routing and forwarding (available onl y on the HP 5500 EI) . Multicast support for VPNs Multicast support for VPNs refers to multicast applied in virtual private networks (VPNs). NOTE: • Multicast support for VPNs is not available in IPv6 networks. • Multicast supporting for VPNs is not available for the HP 5500 SI switches. Introduction to VPN instances VPNs must be isolated from one another and from the public network. As shown in Figure 10, VPN A and VPN B separately access the public network through PE devices.
12 Figure 10 VPN networking diagram • The provider (P) device belongs to the public netw ork. The customer edge (CE) devices belong to their respective VPNs. Each CE device serves its own VPN and maintains only one set of forwarding mechanisms. • The provider edge (PE) devices connect to the public network and the VPNs at the same time. Each PE device must strictly distinguish the information for different networks, and maintain a separate forwarding mechanism for each network. On a PE device, a set of software and hardware that serve the same network forms an instance. Multiple instances can exist on the same PE device, and an instance can reside on different PE devices. On a PE device, the instance for the public network is called the public network instance, an d those for VPNs are called VPN instances. Multicast application in VPNs A PE device that supports multicast for VPNs does the following operations: • Maintains an independent set of independent mu lticast forwarding mechanisms for each VPN, including the multicast protocols, PIM neighbor information, and multicast routing table. In a VPN the device forwards multicast data based on the fo rwarding table or routing table for that VPN. • Implements the isolation between different VPNs. • Implements information exchange and data conv ersion between the public network and VPN instances. As shown in Figure 10, w hen a multicast source in VPN A sends a multicast stream to a multicast group, only the receivers that belong to both the multicast group and VPN A can receive the multicast stream. The multicast data is multicast both in VPN A and in the public network. VPN A VPN A VPN A VPN B VPN B Public networkP PE 1 PE 2 PE 3CE b3 CE a2 CE a3 CE b1 CE a1 CE b2
13 Configuring IGMP snooping Overview Internet Group Management Protocol (IGMP) snooping is a multicast constraining mechanism that runs on Layer 2 devices to manage and control multicast groups. By analyzing received IGMP messages, a Layer 2 devi ce that runs IGMP snooping establishes mappings between ports and multicast MAC addresses, and forwards multicast data based on these mappings. As shown in Figure 11, when IGMP snooping does not run on the Layer 2 switch, multicast packets are fl o o de d to al l devices at Layer 2. When I GM P s noo pi ng ru ns on the Layer 2 swi tch, mu l tic ast packets for known multicast groups are multicast to the receivers, rather than flooded to all hosts at Layer 2. Figure 11 Before and after IGMP snooping is enabled on the Layer 2 device IGMP snooping enables the Layer 2 switch to forward multicast data to only the receivers that require the data at Layer 2. It has the following advantages: • Reducing Layer 2 broadcast packets, thus saving network bandwidth • Enhancing the security of multicast traffic • Facilitating the implementation of per-host accounting Basic concepts in IGMP snooping IGMP snooping related ports As shown in Figure 12, Router A connects to the multicast source, IGMP snooping runs on Switch A and Switch B, and Host A and Host C are receiver hosts (namely, members of a multicast group).
14 Figure 12 IGMP snooping related ports Ports involved in IGMP snooping, as shown in Figure 12, ar e described as follows: • Router port —A router port is a port on an Ethernet switch that leads the switch toward a Layer 3 multicast device (designated router or IGMP querier). In the figure, GigabitEthernet 1/0/1 of Switch A and GigabitEthernet 1/0/1 of Switch B are router ports. The switch registers all its local router ports in its router port list. In this document, a router port is a port on a swit ch that leads the switch toward a Layer 3 multicast device. It is not a port on an ordinary router. • Member port —A member port is a port on an Ethernet sw itch that leads the switch toward multicast group members. In the figure, GigabitEthernet 1/0/2 and GigabitEthernet 1/0/3 of Switch A and GigabitEthernet 1/0/2 of Switch B are member ports. The switch registers all the member ports on the local device in its IGMP snooping forwarding table. Unless otherwise specified, router ports and member ports in this document include both static and dynamic router ports and member ports. NOTE: An IGMP-snooping-enabled switch deems that all its po rts on which IGMP general queries with the source IP address other than 0.0.0.0 or that receive PIM hello messages are received are dynamic router ports. For more information about PIM hello messages, see Configuring PIM (available only on the HP 5500 EI) Aging timers for dynamic ports in IGMP sn ooping and related messages and actions Timer Description Message before expiry Action after expiry Dynamic router port aging timer For each dynamic router port, the switch sets an aging timer. When the timer expires, the dynamic router port ages out. IGMP general query of which the source address is not 0.0.0.0 or PIM hello The switch removes this port from its router port list.