advanced computer networks - cs716 power point slides lecture 26
TRANSCRIPT
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CS716
Advanced Computer Networks
By Dr. Amir Qayyum
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Lecture No. 26
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Internetworking
• Basics of internetworking (heterogeneity)
– IP protocol, address resolution, control messages, …
• Routing
• Global internets (scale)
– Virtual geography and addresses
– Hierarchical routing
• Future internetworking: IPv6• Multicast traffic
• MPLS
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IPv6 Wish List / Planned Support
• 128-bit addresses• Multicast traffic
• Mobility
• Real-time traffic/quality of service guarantees
• Authentication and security
• Autoconfiguration: determining local IP address
• End-to-end fragmentation
• Protocol extensions (flexible protocol)• Smooth transition spread over time is critical
– Islands of v6 and then v4, traffic is tunneled in Internet
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IPv6 Addresses• Classless addressing/routing (similar to CIDR)
• Address notation
– String of eight 16-bit hex values separated by colons
e.g . 5CFA:0002:0000:0000:CF07:1234:5678:FFCD – Only one set of contiguous zeroes can be elided, e.g .
5CFA:0002::CF07:1234:5678:FFCD
• Address assignment
– Provider-based
– Geographic
subscriber ID provider IDregion ID subnet host010
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IPv4 Packet Format Review
• 20-byte minimum
• Mandatory fields not always used (e.g .
fragmentation)
• Options are unordered list of (name, value) pairs
V ersion HLen TOS Length
Ident Flags Offset
TTL Protocol Checksum
SourceAddr
DestinationAddr
Options (variable) Pad (variable)
0 4 8 16 19 31
Data
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IPv6 Packet Format
destination address word 4
destination address word 3
destination address word 2
destination address word 1
source address word 4
source address word 3
source address word 2
source address word 1
payload length next header hop limit
version priority flow label
0 4 8 16 24 31
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IPv6 Packet Format
• 40-byte minimum
• Mandatory fields (probably) always used
• Strict order on options reduces processingtime (no need to parse irrelevant options)
option (variable number, usually fixed length)
destination address (4 words)
source address (4 words)
payload length next header hop limit
version priority flow label0 4 8 16 24 31
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IPv6 Packet Format
• Priority and flow label – Support service guarantees
– Allow “fair” bandwidth allocation
• Payload length (header not included, unlike IPv4)
• Next header
– Combines options and protocol
– Linked list of options
– Ends with higher-level protocol header (e.g . TCP)
• Hop limit is TTL field renamed to match usage
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IPv6 Extension Headers
• Extension headers (options) appear in order
1. Hop-by-hop options .. .. misc. info. for routers
2. Routing .. .. .. .. .. full/partial route to follow
3. Fragmentation .. .. .. IP fragmentation info
4. Authentication .. .. .. sender identification
5. Encrypt security payload info. about contents
6. Destination options .. .. info. for destination
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IPv6 Extension Headers
• Hop-by-hop extension – Length is in bytes beyond mandatory 8
• Jumbogram option (packet longer than 65,535 bytes)
– Payload length in main header set to 0
next header length type
0 8 16 24 31
0 8 16 24 31
value
payload length in bytes
next header 0 194 0
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IPv6 Extension Headers
• Routing extension
– Up to 24 “anycast” addresses target AS’s or providers
– Next address tracks current target
– Strict routing requires direct link, loose routing allows
intermediate nodes
0 8 16 24 31
next header 0 no.of.address
es
next address
strict/loose routing bitmap
1 – 24 addresses
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IPv6 Extension Headers
• Fragmentation extension
• Similar to IPv4 fragmentation
– 13-bit offset, – Last-fragment mark (M)
• Larger fragment identification field
0 8 16 29 31
next header reserved offset Mresvidentification
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IPv6 Extension Headers
• Security without bothering the routers
• Authentication extension
– Designed to be very flexible
– Includes Security Parameters Index (SPI) and
Authentication data at the end
• Encryption extension – Called Encapsulation Security Payload (ESP)
– Includes an SPI
– All headers and data after ESP are encrypted
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IPv6 Design Controversies
Address length
• 8-byte
– Less header overhead. Might run out in a few
decades
• 16-byte
– More overhead. Good for foreseeable future
• 20-byte – Even more overhead. Compatible with OSI
• Variable-length
– Difficult for router design
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IPv6 Design Controversies
Hop limit
• 65,535
– 32-hop paths are common now
– In a decade, much longer paths possible
• 255
– Limits lost packet lifetime (65,535 is far too long)
– Good network design makes long paths unlikely• Source to backbone
• Across backbone
• Backbone to destination
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IPv6 Design Controversies
Maximum packet size
• > 64kB: supercomputer/high bandwidthapplications
– Too much overhead to fragment data
– Want much larger packets
• 64 kB: longer packets incompatible with
low-bandwidth lines – Consider 1MB packet across 1.5 Mbps line
– Ties up line for greater than 5 seconds
– Inconveniences interactive users
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IPv6 Design Controversies
Keep IP checksum ?
• Yes
– Removing checksum from IP analogous to removing
brakes from a car
• Lighter, so you go faster
• Unprepared for the unexpected
• No – Typically duplicated in data link and transport layers
– Major expense in IPv4 routers
– In case of IPv6, it is mandatory in UDP and TCP
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IPv6 Design Controversies
Mobile hosts• Direct or Indirect ?
– Reconnect directly using canonical address
– Use home and foreign agents to forward traffic
• Mobility introduces asymmetry
– Base station signal is strong, heard by mobile units
– Mobile unit signal is weak and susceptible tointerference, not heard by base station
• No clearly superior design proposal
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IPv6 Design Controversies
Security• Where ?
– Network layer: a standard service
– Application layer • No viable standard
• Applications susceptible to errors innetwork implementations
• Too clunky to turn off
• How ?
– Political export/import issues
– Cryptographic strength issues