lecture 15 internetworking: address structure fragmentation and reassembly
TRANSCRIPT
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Lecture 15
Internetworking:
Address Structure
Fragmentation and Reassembly
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Protocol layers across an internetwork
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IP-service model
• Datagram
• Best Effort
• Error reporting
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IP-datagrams crossing a network with various MTU’s
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Header Fields for IP over ethernet
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IP-Address Classes
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IP Addresses
Dotted Decimal Representation
• 01111111.00000101.11111111.00111111
• 255.255.255.255—broadcast address
• 0.0.0.0-forbidden
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Hierarchy and Network Classes
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Datagram Forwarding
• Host and routers with same network address can communicate directly
• Routers exchange packets between networks
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if(NetworkNum of dest.=NetworkNum of one of my interfaces) then deliver packet to destination over that interface
else
if (NetworkNium of dest. is in my forwarding table) then deliver packet to NextHop router
else
deliver packet to default router
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Forwarding table for R2
NetworkNum NextHop
1 R3
2 R1
3 Interface 1
4 Interface 0
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Local Delivery Address Translation
• Address Resolution Protocol (ARP)• ARP request induces the target to broadcast
its IP and Local address across the LAN. Requesting router then knows how to deliver the message
• Target keeps the senders local address and IP address in its own ARP table—in case it needs to ACK
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Host Configuration
• Dynamic Host Configuration Protocol (DHCP)
• DHCP Server-assigns dynamic IP addresses• New hosts broadcast DHCPDISCOVER
message to 255.255.255.255-this message does not go to other networks
• Request may use a DHCP Relay Agent to reach a server on another network
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Error Reporting
• Internet Control Message Protocol (ICMP)– Host unreachable– Reassembly failed– TTL=0– IP header checksum failed– ICMP-Redirect
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Virtual Private Network
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Tunnel Concept
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Forwarding table for router R1
NetworkNum NextHop
1 Interface 0
2 Virtual interface 0
Default Interface 1