Transcript Chapter9

Computer Networks
Chapter 9 – Network Layer Addresses
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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Network Address Examples
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IP – per interface
IPX – per interface
IPv6 – per interface
CLNP – per node
AppleTalk – per interface
DECnet – per node
LAN A
Interface 0
Host
X
Interface 1
LAN B
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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Hierarchical Addresses, Fixed Bdry
• N nodes in network, N large
• N too big to keep routing info with N rows
• Aggregate addresses so all nodes in one
area have same prefix…. Hierarchical
• Balance size K of subnetwork with number
of subnetworks L
• Introduce more levels if K and L too big
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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Hierarchical Addresses, Fixed Bdry
•Level i+1 routers route
amongst Level i
networks;
•Level 1 routers route to
end nodes in same
subnetwork
37.*.*
22.*.*
41.*.*
Level 2 subnetworks
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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Hierarchical Addresses, Fixed Bdry
37.23.*
37.3.*
37.1.*
37.12.*
Level 2
Level 1
subnetwork subnetwork
22.23.*
41.12.*
41.97.*
3-level address:
22.56.*
41.5.*
22.3.*
22.12.*
41.17.*
22.1.*
end
host
Level 3 subnetworks
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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Hierarchical Addrs, Flexible Bdry
• Really, no need for
router to know its level
• No need to have fixed
fields for address levels
• Subnet address is just a
prefix
5221*
722*
71*
723*
7*
backbone
5*
31*
522*
55*
315*
311*
551*
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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Owning vs. Renting
• Initially, IP addresses obtained in blocks
from IANA
• Blocks given according to size and order
of request
• Results in non-topological addresses
• Now addresses given to providers
• Providers distribute sub-addresses
• Address must change with provider…
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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Address Types
• Unicast – single node destination
• Multicast – group of nodes destination
• Broadcast – all nodes are destinations
– May restrict to subnetwork
– May restrict number of hops
• Anycast – to any one of a group of nodes
– Useful for service discovery
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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IPv4 Addresses
• RFC 791 – generically, IP
• 4 octets long (32 bits)
• Link and host parts (boundary varies with
subnetwork)
• Subnet mask used to define boundary
– 1’s where subnet bits are, 0’s for host bits
– In practice, contiguous bits
• Address depends on subnetwork!
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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Obtaining IP Addresses
• Manually configured address and mask
• Obtain from server
– BOOTP (RFC 951)
– DHCP (RFC 1531)
– RARP (RFC 903)
– Start with LAN address, and either broadcast
to or know address of server (BOOTP, DHCP)
– Server provides mask and address
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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IPv4 Addresses (original)
Dotted Decimal
0
net
1.0.0.0 to
127.255.255.255
host
Class A address
10
net
128.0.0.0 to
191.255.255.255
host
Class B address
110
net
host
Class C address
1110
Multicast address
Class D address
11110
reserved
Class E address
192.0.0.0 to
223.225.225.225
224.0.0.0 to
239.225.225.225
240.0.0.0 to
247.255.255.255
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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Special IPv4 Addresses
Dotted Decimal
0.0.0.0
00000000000000000000000000000000
This host
000000…0000000
0.x.y.z
host
Host on this network
11111111111111111111111111111111
225.225.225.225
Broadcast on local network
net
111111…11111
Broadcast on remote network
127
anything
127.a.b.c
loopback
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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Subnet Mask
10
network
subnetwork
host
Network address
11111111111111111111111111
000000
Subnet mask
• Flexible subnet mask not supported by old
routing protocols (RIP, EGP, early BGPs)
• Solves “Three Bears Problem”
• CIDR
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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CIDR
• Classless InterDomain Routing (RFC 1519)
• Specify subnet by dotted decimal (filling in
host part with 0’s)/<bits in network address>
• Example: 227.128.64.64/27 has
32-27=5 bits of host address
• Allows geographic distribution of Class C’s:
– 194.0.0.0 – 195.255.255.255 to Europe
– 198.0.0.0 – 199.255.255.255 to Africa
– 200.0.0.0 – 201.255.255.255 to Cent. & So. Amer.
– 202.0.0.0 – 203.255.255.255 to Asia & Pacific
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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IPX Addresses
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10 bytes long
Top 4 are network part
Bottom 6 are node part
Autoconfiguration –
– node part = MAC addr on IEEE 802 LANs
• Also easy to get MAC addr from IPX addr
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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IPX+ Addresses
• 16 bytes long
• New top 6 are domain number
– Obtained automatically from service provider
• Bottom 10 as before
• One mode of IPv6 resembles this
• Extra header added after IPX header
– Old routers only look at old header
• In domain, route on 4 byte net part
• Boundary routers route on 6 byte domain
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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IPv6 Addresses
• 16 byte addresses (128 bits)
• A.k.a. IPng (next generation)
– Needed as 32-bit address space “ran out”
• Has separate Ethertype (naughty bridges)
• Addresses (see RFC 2373) written as
– Colon separated hex – 0:0:0:0:0:0:E87F:4001
– Shortcut 0’s - ::E87F:4001
– Allow dotted decimal IP addresses in last 32 bits
::228.127.64.1
• Prefix written as address/prefix length (CIDR)
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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EUI-64
• IEEE defined 8-byte address space for
“next-generation” LANs
• EUI-48 is standard 48-bit address
• How to expand?
– Longer OUI, same address block?
– Same OUI, longer address block?
• Consider implications…
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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IPv6 Address Conventions
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::0 (this network and node)
::1 (loopback)
::IPv4 (bottom 32 bits IPv4 address, rest 0)
::FFFF:IPv4 (bottom 32 bits are IPv4, next are FFFF, rest 0 – for
IPv4 only nodes)
2000::/3 (normal aggregatable unicast – bottom 8 bytes is EUI-64*
node address)
FE80::/10 (link-local – bottom 8 bytes EUI-64*, not to be forwarded)
FEA0:/10 (site-local – bottom 8 node, next 2 subnet ID, not sent offsite)
Anycast – link prefix, then all 0’s
FF00::/8 (Multicast – flags/8, scope/4, then 112 bits of address)
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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IPv4 to IPv6 Transition
• IPv6 specification delayed
• IPv4 improvements made meanwhile:
– CIDR addressing, variable subnet masks
– DHCP for address configuration & reuse
– NAT address sharing & reuse
• Dual stack nodes
• Translators (NAT, e.g.)
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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CLNP Addresses
• Connectionless Network Layer Protocol
• ISO defined, used by DECnet Phase V,
ATM, CDPD (cellular digital packet data)
• Variable length addresses, max 20 octets
• Extra octet to specify length
• Area/ID(0-8)/SEL(1)
– Area is larger than single link – like network
– ID has no topological significance – like MAC
– SEL is like DSAP/SSAP or protocol
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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CLNP Addresses
IDP
AFI
IDI
Globally
defined
DSP
ID
SEL
Locally
defined
0-8
octets
1
octet
• Globally defined part is variable
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–
–
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IDP = initial domain part
AFI = Authority and Format Identifier
IDI = Initial Domain Identifier
DSP = Domain-specific Part
• Locally defined part also variable (>=2)
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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AppleTalk Addresses
• 3 byte addresses
– 2 bytes net (can specify range for large LAN)
– 1 byte node
• Autoconfiguration
– See chapter 11!
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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DECnet Addresses
• Phase III – 2-byte addresses, no hierarchy
• Phase IV – 2-byte addresses
– 6 bit area
– 10 bit node
• Used CLNP for packet format – delayed…
• Map DECnet address to Ethernet
– Force top 4 bytes to be AA-00-04-00
– Reassign NIC address when DECnet boots
– Better boot first!
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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Network Address Translation (NAT)
• NAT box has set of globally unique
network addresses it can assign
• Local nodes have only locally significant
addresses
• NAT assigns global address to local node
• Extend by assigning (address,port) pairs
to (address,port) pairs
• Issues with addresses passed (FTP), etc.
CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman
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