09-Addressing - IP Addressing and Forwarding EE122 Fall...

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1 IP Addressing and Forwarding EE122 Fall 2011 Scott Shenker http://inst.eecs.berkeley.edu/~ee122/ Materials with thanks to Jennifer Rexford, Ion Stoica, Vern Paxson and other colleagues at Princeton and UC Berkeley
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Announcements • Submission instructions have been sent – Does everyone understand? – Please make sure your instructional account works • Switching to 122: awaiting instructions 2
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Agenda for Today • Quick Security Review • IP Addressing • IP Forwarding And an anagram contest! 3
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Quick Security Analysis of IP Packet Header More for mindset than content The workings of a paranoid mind…. . 4
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Focus on Sender Attacks • Ignore (for now) attacks by others: – Traffic analysis – Snooping payload – Denial of service • Focus mostly on vulnerabilities sender can exploit 5
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IP Packet Structure 4-bit Version 4-bit Header Length 8-bit Type of Service (TOS) 16-bit Total Length (Bytes) 16-bit Identification 3-bit Flags 13-bit Fragment Offset 8-bit Time to Live (TTL) 8-bit Protocol 16-bit Header Checksum 32-bit Source IP Address 32-bit Destination IP Address Options (if any) Payload
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7 IP Address Integrity • Source address should be the sending host – But, who’s checking? – You could send packets with any source you want Why is checking hard?
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8 Implications of IP Address Integrity • Why would someone use a bogus source address? • Launch a denial-of-service attack – Send excessive packets to the destination – … to overload the node, or the links leading to the node – But: victim can identify/filter you by the source address • Evade detection by spoofing – Put someone else’s source address in the packets o Or : use many different ones so can’t be filtered • Or: as a way to bother the spoofed host – Spoofed host is wrongly blamed – Spoofed host may receive return traffic from the receiver
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9 More Security Implications • Version field (4 bits) …. ? – Issue: fledgling IPv6 deployment means sometimes connectivity exceeds security enforcement – E.g., firewall rules only set up for IPv4 • Header length (4 bits) …. ? – Controls presence of IP options o E.g., Source Route lets sender control path taken through network - say, sidestep security monitoring – IP options often processed in router’s slow path o Allows attacker to stress router for denial-of-service – Firewalls often configured to drop packets with options.
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10 Security Implications of TOS? (8 bits) • Attacker sets TOS priority for their traffic? – If regular traffic does not set TOS, then network prefers the attack traffic , greatly increasing damage • What if network charges for TOS traffic … – … and attacker spoofs the victim’s source address?
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This note was uploaded on 01/09/2012 for the course ELECTRICAL 122 taught by Professor Shenker during the Spring '11 term at University of California, Berkeley.

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09-Addressing - IP Addressing and Forwarding EE122 Fall...

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