1. Part I: Core networking concepts Naming & Addressing

2. Names and addresses Names are identifiers –Used by end users / applications to interact with your system system components to interact with each other –Name operators compare, resolve, bind/un-bind Addresses: names that locate objects Good names should be decoupled from addresses

3. Names or addresses? NYU ID /home/jinyang/doc/lec2.ppt www.nytimes.com 199.239.137.245 http://www.nytimes.com/world 00:18:8B:06:DC:CB BitTorrent: f22bd0823..c86a5

4. Addresses

5. Design considerations Addresses are used by routers to forward packets to an endpoint Should be uniquely allocated Don’t have to be user-friendly Should enable scalable routing

6. IP address evolution Original scheme: –8-bit net (area) / 24-bit host (intra-area) Why distinguishing net and host? Why’s wrong with 8-bit net? –256 is not enough nets –Most networks don’t have 16 million hosts

7. Class-based IP address MIT 18.*.*.* Apple 17.*.*.* NYU 128.122.*.* Microsoft 207.46.*.*

8. Forwarding based on class- based address 1.Examine first 1/2/3 bits, 2.Perform a lookup according to net #

9. Class-based --> CIDR Why not class-based addresses? –Class A is wasteful! –Too many organizations are > C, but < B –Too many entries at routers CIDR: classless inter-domain routing –Represent net size explicitly 216.239.32.0/19 61.135.0.0/16 –Allocate appropriate size –Allocate hierarchically

10. Hierarchical allocation Sprint At&t ISP Another ISP 12.0.0.0/8 12.4.0.0/16 12.4.240.0/20

11. Forwarding w/ CIDR addresses Longest prefix match –12.4.225.69 matches 12.24.225.0/20 instead of 12.0.0.0/8 Non-trivial –10-100 millions pkts/sec –Memory latency 5-10 ns

12. Still not enough IP address? NAT (Network address Translator) Maps external address/port pairs to internal address/port pairs –Rewrites src/dst addresses! NAT breaks –global reachability –Protocols that identify host w/ IP addresses

13. IPv6 128-bit addresses –Different classes of addresses –Hierarchically allocated addresses like CIDR –Lower 64-bits are interface ID Simplified header format –40 bytes as opposed to 20 in IPv4

14. IPv6 deployment options Embed v4 addresses in low bits of IPv6 Tunnel IPv6 packets over IPv4 networks Applications must be dual-stacked or use a v4-to-v6 translator

15. IPv6 deployment status

16. Names

17. Design Considerations Ensuring uniqueness 1.Central naming authority 2.Hierarchical delegation 3.Pseudo-randomly 4.Content hashes Intended audience: humans or machines?

18. DNS Why domain names? –IP addresses are not user friendly –Need topology-independent names Early 80s: hosts.txt file, maps host name  IP DNS: distributed service, maps domain name  IP –Record types: A, NS, MX, CNAME, PTR …

19. Deep hierarchy Hierarchical names enable delegation.com.edu.gov.cn.uk.nyu.cs.news. flat www

20. Resolving hierarchical names Stub resolver application cs.nyu.edu DNS server root name server.com name server.google.com name server Root servers might become bottlenecks? Long latency? Query: www.google.com Response:.com NS a.gtld-servers.nett Q: www.google.com R: google.com NS ns1.google.com Q: www.google.com R: www.google.com A 216.239.32.10

21. Replicating servers for capacity/availability Each sub-tree (zone) is kept at  2 name servers 13 root servers –[A-M].root-servers.net –Geographically diverse: VA, CA, MD, Japan etc. Another 13 name servers for.com,.net

22. Caching Stub resolver cs.nyu.edu DNS server root name server com name server google name server Query: www.google.com Response:.com NS a.gtld-servers.nett Q: www.google.com R:.google.com NS ns1.google.com Q: www.google.com R: www.google.com A 216.239.32.10.com NS.google.com NS www.google.comwww.google.com A All record types are cached according to TTL Caching NS records is effective at reducing latency Stub resolver Stub resolver

23. Caching, continued Cache negative response –10-42% lookups result in a neg answer –Most neg answers are for reverse IP lookups Setting low TTL for A records harmful? –Not really [Jung et. al. 2002] –Most DNS cache hits happen in short succession Sharing DNS caches at multiple sites useful? –Not really –Names follow zipf distribution, misses are for rare names

24. “Innovative uses” of DNS load balancing/server selection DNS server returns different A records to different clients at different times Short TTL: e.g. 60 sec for Akamai

25. “Innovative” uses of DNS spam blacklisting Is 125.191.168.35 a spam source? Resolve name 35.168.191.125.bl.spamcop.net

26. Problems with current naming/addressing

27. A layered naming architecture “Almost every problem in computer science can be solved by another level of indirection” -- David Wheeler 70s

28. LNA Proposal overview User level descriptor (ULD) e.g. email, search string SID EID IP Youtube -> (SID_a5f4) SID_a5f4 -> (EID_365a, TCP, port 80) EID_365a -> IP_12.4.224.3

29. Claimed Advantage #1: Host mobility Authors’ claim –TCP breaks if hosts change IPs –Difficult to initiate connection to mobile host How LNA solves it? Devil’s advocate

30. Claimed Advantage #2: Service/data migration/replication Authors’ claim –URL-based links break if domain name changes –No name for replicated data How LNA solves it? Devil’s advocate

31. Claimed Advantage #3: Accommodating middle boxes Authors’ claim –No explicit support for network-level middle boxes –No explicit support for application-level middle boxes Devil’s advocate