IPv4 addresses basically come in three flavors Public, Private and Multicast. The main difference between Public and Private addresses is the fact that private addresses are not rotatable on the Internet. They actually are, but ISP’s put measures in place to block the routing of private addresses. This design is not by accident, and has allowed IPv4 to survive as long as it has. Even with the recent depletion of IPv4 addresses large and small Corporations continue to run their networks behind Network Address Translation, and will continue to do so for years to come.
Where n = networks, and h = hosts
IPv4 Address Space
- A – [ 00000000 ] to [ 01111111 ] Range 0 to 127
- A – [ 10.0.0.0 – 10.255.255.255 ] = 16,777,216
- B – [ 10000000 ] to [ 10111111 ] Range 128 to 191
- B – [ 172.16.0.0 – 172.31.255.255 ] = 1,048,576
- C – [ 11000000 ] to [ 11011111 ] Range 192 to 223
- C – [ 192.168.0.0 – 192.168.255.255 ] = 65,536
RFC 1918 Private Address Space
- A – [ 10.0.0.0 – 10.255.255.255 ]
- B – [ 172.16.0.0 – 172.31.255.255 ]
- C – [ 192.168.0.0 – 192.168.25.255 ]
Link Local Address Range
- 169.254.0.0 to 169.254.255.255
- 224.0.0.0 to 224.0.0.255
- TTL = 1
Positional Values
- 128, 64, 32, 16, 8, 4, 2, 1
- High order: 128 + 64 + 16 = 240
- Low order: 8 + 4 + 2 + 1 = 15
- High + Low: 240 + 15 = 255
Building Subnet Blocks
Building [ 1 ] network block from 172.16.1.0/24
Block bits: 2^0 = 1
Block host bits: 2^8 – 2 = 254
Block = .0 Broadcast = .255
Building [ 2 ] network blocks from 172.16.1.0/25
Block bits: 2^1 = 2
Block hosts bits: 2^7 – 2 = 126
Blocks: .0 .127 Broadcasts: .126 .255
Building [ 4 ] network blocks from 172.16.1.0/26
Block bits: 2^2 = 4
Block host bits: 2^6 – 2 = 62
Blocks: .0 .64 .128 .192 Broadcasts: .63 .127 .191 .255
Building [ 8 ] network blocks from 172.16.1.0/27
Block bits: 2^3 = 8
Block host bits: 2^5 – 2 = 30
Blocks: .0 .32 .64 .96 .128 .160 .192 .224 Broadcasts: .31 .63 .95 .127 .159 .191 .223 .255
Building [ 16 ] network blocks from 172.16.1.0/28
Block bits: 2^4 = 16
Block host bits: 2^4 – 2 = 14
Blocks: .0 .16 .32 .48 .64 .80 .96 .112 .128 .144 .160 .176 .192 .209 .224 .240 Broadcasts: .15 .31 .47 .63 .79 .95 .111 .127 .143 .159 .175 .191 .208 .223 .239 .255
Building [ 32 ] network blocks from 172.16.1.0/29
Block bits: 2^5 = 32
Block host bits: 2^3 – 2 = 6
Blocks: .0 .8 .16, .24 .32 .40 .48 .56 .64 .72 .80 .88 .96 .104 .112 .120 .128 .136 .144 .152 .160 .168 .176 .184 .192 .200 .208 .216 .224 .232 .240 .248
Broadcasts: .7 .15 .23 .31 .39 .47 .55 .63 .71 .79 .87 .95 .103 .111 .119 .127 .135 .143 .151 .159 .167 .175 .183 .191 .199 .207 .215 .223 .231 .139 .247
Building [ 64 ] network blocks from 172.16.1.0/30
Block bits: 2^6 = 64
Block host bits: 2^2 – 2 = 2
Blocks: .0 .4 .8 .12 .16 .20 .24 .28 .32 .36, .40 .44 .48 .52 .56 .60 .64 .68 .72 .76 .80 .84 .88, .92 .96 .100 .104 .108 .112 .116 .120 .124 .128 .132 .136 .140 .144 .148 .152 .156 .160 .164 .168 .172 .176 .180 .184 .188 .192 .196 .200 .204 .208 .212 .216 .220 .224 .228 .232 .236 .240 .244 .248 .252 Broadcast: .3 .7 .11 .15 .19 .23 .27 .31 .35, .39 .43 .47 .51 .55 .59 .63 .67 .71 .75 .79 .83 .87, .91 .95 .99 .103 .107 .111 .115 .119 .123 .127 .131 .135 .139 .143 .147 .151 .155 .159 .163 .167 .171 .175 .179 .183 .187 .191 .195 .199 .203 .207 .211 .215 .219 .223 .227 .231 .235 .239 .243 .247 .251
IPv4 Multicasting
The processes of mapping Layer 3 to Layer 2 addresses is accomplished with the help of a special 24 bit HEX value of 01:00:5E. This special reserved 24 bit address prefix makes up half the Layer 2 address. Fortunately mapping the renaming portion of the address is very simple. All we need to do is take the remaining 23 bits ( 24 – 1 ) bits of the Layer 3 address and simply convert into HEX, and added to the remaining portion.
Class D Range – [ 224.0.0.0 – 239.255.255.255 ]
- Link Local – [ 224.0.0.0 – 224.0.0.255 ]
- Globally Scoped – [ 224.0.1.0 – 238.255.255.255 ]
- Source Specific – [ 232.0.0.0 – 232.255.255.255 ]
- GLOP – [ 223.0.0.0 – 223.255.255.255 ]
- Limited Scope – [ 239.0.0.0 – 239.255.255.255 ] – Similar to RFC 1918
Link Local Examples
- 169.254.0.0/16 –169.254.255.255
- Range – [ 224.0.0.0 – 224.0.0.255 ]
- RIPv2 – 224.0.0.9
- EIGRP – 224.0.0.10
- OSPF – 224.0.0.5 – 224.0.0.6
- TTL = 1
Reverse Path Forwarding
- If ingress ( multicast ) traffic is observed on multiple interfaces
- Use the underlying IGP unicast routing protocol to forward the traffic out the correct interface
Protocol Independent Multicast
- PIM Dense Mode: Builds source distribution trees
- PIM Sparse Mode: Builds unidirectional shared trees rooted at a Rendezvous Points or RPs
Rendezvous Points
- Static RP – As the name implies it’s a static configuration
- Auto RP – Advertise availability automatically
Internet Group [ Management ] Protocol
In a typical deployment IGMPv1, IGMPv2 or IGMPv3 would be configured on Routers, and Clients. The IGMP Snooping Protocol would be configured within the Switching infrastructure. The IGMPv1 or IGMPv2 Protocol on the Routers will manage the group Joins and Leaves such as ( *, G ) and ( S, G ) join messages. For example an IGMP join message might look something like this ( *, 239.0.0.5 ) where the star in the source is independent. A source specific join might look like something like this ( 239.0.0.20, 239.0.0.5 ) etc. The IGMP protocol will send Joins in the form of a IGMP Report messages such as flooding, pruning, and grafting.
- IGMPv1
- IGMPv2 – Leave Messages
- IGMPv3 – Leave Messages + Source Specific – [ 232.0.0.0 – 232.255.255.255 ]
- IGMP Snooping
- 60 Second update timer
Conversion Example
Remember when converting from Layer 3 to Layer 2 the first half of the [ MAC address ] is already done 01:00:5E. Overlapping can occur depending on the address range..!
- Address: 239.1.10.10
- Convert the last [ three ] octets in this case 1.10.10
- 0000.0001 0000.1010 0000.1010
- Flip the left most bit to 0 if it’s not already 0
- Convert 0000.0001 0000.1010 0000.1010 into HEX
- 0000.0001 = 01
- 0000.1010 = 0a
- 0000.1010 = 0a
- 01.0a.0a
- 01:00:5E.01.0a.0a
