Multicast Addresses. IPv4 Multicast Address Blocks. IPv4 Multicast Addresses. Multicast Group. IPv4 Multicast Addresses Class D addresses

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1 Multicast Addresses IPv4 Multicast Addresses Class D addresses Multicast Group Each different address a different multicast group 2 28 groups max Allocation is the problem As with all addresses Here no topology to consider Assignment of blocks by usage number assignment within blocks varies IPv4 Multicast Address Blocks Local Net Control Internet Control Ad-Hoc (as needed) ST Multicast Groups (IPv5) SDP/SAP And others About half address space currently reserved Not to be used IPv4 Multicast Addresses Local Net Control Packets not to be forwarded by routers Local routing/discovery/ All systems (hosts) All Routers DVMRP Routers OSP Routers OSP Designated Routers RIP2 Routers IGMP (v3 reports)

2 IPv4 Multicast Addresses Internet Control Packets that traverse the Internet Varied Uses NTP (Time) SGI Dogfight IET Meeting Broadcasts Music Service Service Location (SVRLOC) SVRLOC Directory Agents CNN IPv4 Multicast Addresses Ad Hoc Blocks of Addresses Protocols that need more than one address But Less than 256 /24 block usually allocated (or smaller) Amex MDD Service Where Are You Dow Jones SDP/SAP Multimedia Conference Calls SAP (v1) Announcements SAP Dynamic Assignments Multicast Group Distribution Anyone can join any multicast group Packets will be forwarded Not always desirable Want a way to limit destinations Where recipients can be Want sender to choose not rely upon filters in routers groups too dynamic irst method IP header Time To Live TTL limits packet distribution TTL == 1 packet remains on link TTL == 2 packet no further than neighbours (etc)

3 TTL Scopes D Have network with multicast nodes And link to outside world ( ) Want to use multicast inside organisation Nothing escape to outside TTL Scopes A Host A can send with TTL == 4 A TTL Scopes D TTL=3 A TTL=4 Host D TTL=3 can send with TTL=3 == 3

4 TTL Scopes Host causes problems With TTL=2 TTL Scopes TTL=2 Host causes problems With TTL=4 TTL Scope Boundaries drop TTL=2 TTL=0 drop TTL=3 TTL>= 32 drop TTL=4 Administrative boundary at exit TTL=3 router Affects multicast packets only Packet with TTL < limit dropped at exit router Packet with TTL >= limit passed through TTL decremented by 1 TTL=3

5 TTL Scopes Several TTL boundaries suggested Countries Organisations Departments Link -> easy Organisations invented their own By selecting a TTL just under boundary packet can be locked in Requires careful config of routers exit routers particularly Stretching the definition of TTL some topologies will fail Selecting scope boundary TTL values a black art... (magic) Scopes in Addresses Usually address selects destination With TTL scoping TTL is just as important Administrative scoped addresses created groups Address range divided into smaller blocks Local Scope Region of undetermined size But no internal boundaries Any scope boundary ends local scope , ,... when required (/14) (RC2365) (IANA) Organisation Local Scope Scopes in Addresses /24 Link Local, existed already Global scope is "the rest" or defined blocks Scope boundaries assigned administratively Rules for how scopes laid out Overlapping possible But a little tricky Scopes must be connected convex Boundaries easy to get wrong Don t rely upon them for sensitive information Addresses mostly assigned dynamically needs a protocol

6 Relative Addresses Within admin scoped blocks local scope organisation scope Highest / /24 for local scope reserved for relative assignments intended for finding other multicast addresses Relative Assignments Allocated addresses for all blocks Apply for a purpose within the scope Subtract relative address from highest possible address gives a multicast group address SAP Announcements Relative address in local scope in organisation scope v6 Multicast Addresses IPv6 Multicast Address 0x lagsscope Group Identifier Similar to IPv4 2 new fields lags Two bits defined T 0001 Transient Address P 0010 Prefix Address (RC3306) Scope Limits distribution of Multicast 1 Node Local 2 Link Local 5 Site Local 8 Organisation Local E Global v6 scopes came first v4 copied them v6 Multicast Addresses Different Scopes Different Addresses (Groups) Application wanting same group in different scopes must join each group Address Assignments Similar to IPv4 Node Local 01::1 - All Nodes 01::2 - All Routers Link Local 02::1 - All Nodes 02::2 - All Routers 02::4 - DVMRP Routers Site Local 05::2 - All Routers 05::3 - All DHCP Servers

7 ARP/ND for Multicast? Before transmitting an IP packet over ethernet (and similar) IPv4 host does ARP translate IPv4 address to Ethernet address IPv6 host does ND (Neighbour Discovery) similar purpose or multicast destinations Does that work? Who would reply? Everyone in multicast group? What Ethernet address would they send? Where did they get that from? If recipient can find out Link Level address needed to join the group all nodes must use the same one Can t sender do it the same way? Ethernet IP Multicast No dynamic protocol Algorithmic conversion rom IP address to Link address Multicast Ethernet Addresses L G mmmmmm 0 1 mmmmmmmmmmmmmmmm g g g g g g g g g g g g g g g g g g g g g g g g Need a manufacturer code (mmmmmm) Then have 2 24 multicast addresses With several manufacturer codes could have more multicast addresses IANA has a manufacturer code 00:00:5E Allocated part for IP multicast One code thought sufficient Ethernet IP Multicast Mapping Algorithm Least significant 23 bits of IPv4 address Are the least significant 23 bits of Ethernet address Examples: :00:5E:00:00:01 Note G bit is set (first 01) Bottom 23 bits the same in both forms :00:5E:7:: Note only 23 bits :00:5E:00:00:01 Same ethernet address as Each Ethernet address is generated by 32 IPv4 multicast addresses Software must filter unwanted packets