Table of Contents
Historical Classes of networks
|Class||Leading bits||Range||Subnet/Classful/Natural mask|
|A||0||0.0.0.0 - 127.255.255.255|
Cisco says 126.x.x.x
- 127.0.0.1 used for local loopback
|B||10||188.8.131.52 - 184.108.40.206||255.255.0.0|
|C||110||192.0.0.0 - 220.127.116.11||255.255.255.0|
|D (multicast)||1110||18.104.22.168 - 22.214.171.124||126.96.36.199-188.8.131.52 are global scoped - can be used across Internet|
|E (reserved)||1111||240.0.0.0 - 255.255.255.255|| |
- Class of IP address entirely determined by value of first octet.
- Public routable ip addrs managed by ICANN - Internet Corporation for Assigned Names and Numbers - assign to registries (e.g. ARIN - American Registry for Internet Numbers, IANA (outside of NA) - Internet Assigned Numbers Authority)
- InterNIC - Internet Network Information Center - old org that did ICANN's job
One to one traffic
- dhcp - dynamic host configuration protocol, cisco says use even on small networks
- APIPA - Auto Priv IP Addr - not routeable
255.255.255.255 everywhere on our subnet
192.168.100.255/24 local subnet/directed broadcast on any subnet
endpoints join a group (e.g. group with addr 184.108.40.206)
Registered multicast addrs
220.127.116.11 Base Address (Reserved) [RFC1112][JBP]
18.104.22.168 All Systems on this Subnet [RFC1112][JBP]
22.214.171.124 All Routers on this Subnet [JBP]
126.96.36.199 Unassigned [JBP]
188.8.131.52 DVMRP Routers [RFC1075][JBP]
184.108.40.206 OSPFIGP OSPFIGP All Routers [RFC2328][JXM1]
220.127.116.11 OSPFIGP OSPFIGP Designated Routers [RFC2328][JXM1]
18.104.22.168 ST Routers [RFC1190][KS14]
22.214.171.124 ST Hosts [RFC1190][KS14]
126.96.36.199 RIP2 Routers [RFC1723][GSM11]
188.8.131.52 IGRP Routers [Farinacci]
184.108.40.206 Mobile-Agents [Bill Simpson]
220.127.116.11 DHCP Server / Relay Agent [Unknown]
18.104.22.168 All PIM Routers [Farinacci]
See http://www.iana.org/assignments/multicast-addresses/ for a complete list.
Overview of how multicast works
Quoted from http://www.cisco.com/en/US/tech/tk828/technologies_white_paper09186a0080092942.shtml.
- The client sends an IGMP join message to its designated multicast router. The destination MAC address maps to the Class D address of group being joined, rather being the MAC address of the router. The body of the IGMP datagram also includes the Class D group address.
- The router logs the join message and uses PIM or another multicast routing protocol to add this segment to the multicast distribution tree.
- IP multicast traffic transmitted from the server is now distributed via the designated router to the client's subnet. The destination MAC address corresponds to the Class D address of group
- The switch receives the multicast packet and examines its forwarding table. If no entry exists for the MAC address, the packet will be flooded to all ports within the broadcast domain. If a entry does exist in the switch table, the packet will be forwarded only to the designated ports.
- With IGMP V2, the client can cease group membership by sending an IGMP leave to the router. With IGMP V1, the client remains a member of the group until it fails to send a join message in response to a query from the router. Multicast routers also periodically send an IGMP query to the "all multicast hosts" group or to a specific multicast group on the subnet to determine which groups are still active within the subnet. Each host delays its response to a query by a small random period and will then respond only if no other host in the group has already reported. This mechanism prevents many hosts from congesting the network with simultaneous reports.
- In order to limit broadcast domain.
- WAN link that only needs 2 addrs
- interesting octet - the last subnet mask byte - uses borrowed bits
- Subnets created = 2^s where s is number of borrowed bits
- 192.168.1.0 24 bits natural mask
- if we borrow 3 bits - we have 2^3 = 8 subnets
- available hosts = 2^h - 2 where h is number of host bits in subnet mask
- 192.168.1.0 8 host bits
- 2^8 - 2 = 253
network addr 172.16.0.0 255.255.224.0 or /19 subnet
directed broadcast 172.16.31.255 (1s for host bits)
usable ip addrs 172.16.0.1 - 172.16.31.254
Private IP ranges (RFC1918)
10.0.0.0 - 10.255.255.255 (10/8) def subnet mask 255.0.0.0
172.16.0.0 - 172.31.255.255 (172.16/12) def subnet mask 255.255.0.0
192.168.0.0 - 192.168.255.255 (192.168/16) def subnet mask 255.255.255.0
link-local/self assigned address
169.254.0.0 - 169.254.255.255 (169.254/16) def subnet mask 255.255.0.0
APIPA (Auto Priv IP Addressing) 0 non-routable addr assigned to a host that did not hav ip addr manually or dynamically assigned
- should not be sent to router for routing
- TTL should be 1
192.0.2.0 - 192.0.2.255 (192.0.2.0 /24)
- VLSM - Variable Length Subnet Masks - don't have to do subnetting on classful boundaries.
- CIDR - Classless Inter-Domain Routing (RFC1519) - Uses VLSM to allow a subnetting network/host boundaries to happen on any bit boundary.
IP Packet - (RFC791)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
|Version4| IHLInternet Header Length is
the length of the internet
header in 32 bit words,
and thus points to the
beginning of the data.
Note that the minimum
value for a correct header
is 5 32-bit words. |Type of Service| Total Lengthentire packet size,
including header and data,
in bytes |
| IdentificationIDs fragments for
reassembly |FlagsBit 1 - Do Not Frag (1)
Bit 2 - More Frags (1)| Fragment Offset |
| Time to Livenum of hops until pkt
is dropped. Keeps routing
loops from happening. | Protocole.g. | Header Checksum |
| Source Address |
| Destination Address |
| Options | Padding |
| Data ... |
- Protocol Numbers
- ICMP (Protocol 1)
- TCP (Protocol 6)
- UDP (Protocol 17)
see http://www.iana.org/assignments/protocol-numbers for more...