CS615 - Aspects of System Administration
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1 CS615 - Aspects of System Administration Slide 1 CS615 - Aspects of System Administration DNS; HTTP Department of Computer Science Stevens Institute of Technology Jan Schaumann jschauma@stevens-tech.edu
2 Current Events CS615 - Aspects of System Administration Slide Tb/s DDoS on GitHub
3 Current Events CS615 - Aspects of System Administration Slide 3 Reminder: The Cloud is just other people s computers. AWS US-EAST-1 Region downtime leads to outages and connectivity degradation for Atlassian s Bitbucket, Confluence, and Jira, GitHub, MongoDB, NewVoiceMedia, Slack, Twilio, Zillow.
4 Keeping track... CS615 - Aspects of System Administration Slide
5 In the beginning... CS615 - Aspects of System Administration Slide 5
6 In the beginning... CS615 - Aspects of System Administration Slide 6
7 In the beginning... CS615 - Aspects of System Administration Slide 7
8 In the beginning... CS615 - Aspects of System Administration Slide 8
9 In the beginning... CS615 - Aspects of System Administration Slide 9
10 In the beginning... CS615 - Aspects of System Administration Slide 10
11 In the beginning... CS615 - Aspects of System Administration Slide 11 # Host Database # This file should contain the addresses and aliases # for local hosts that share this file. # localhost localhost. # # RFC 1918 specifies that these networks are "internal". # # # UCLA-TEST SRI-SPRM UTAH-CS
12 But then... CS615 - Aspects of System Administration Slide 12
13 The Domain Name System CS615 - Aspects of System Administration Slide 13 Computers like numbers
14 The Domain Name System CS615 - Aspects of System Administration Slide 14 Computers like numbers
15 The Domain Name System CS615 - Aspects of System Administration Slide 15 People like names. ash.cs.stevens-tech.edu
16 The Domain Name System CS615 - Aspects of System Administration Slide 16
17 The New Phonebook is here! CS615 - Aspects of System Administration Slide 17 wget -q -O - grep -c "^HOST"
18 DNS: A distributed database CS615 - Aspects of System Administration Slide 18
19 The Domain Name Space CS615 - Aspects of System Administration Slide 19 The domain name space consists of a tree of domain names.
20 DNS: A hierarchical system CS615 - Aspects of System Administration Slide 20
21 The Domain Name Space CS615 - Aspects of System Administration Slide 21 The domain name space consists of a tree of domain names. A subtree divides into zones.
22 The Domain Name Space CS615 - Aspects of System Administration Slide 22 The domain name space consists of a tree of domain names. A subtree divides into zones. Each node may contain resource records.
23 The Domain Name Space CS615 - Aspects of System Administration Slide 23
24 Domain Names CS615 - Aspects of System Administration Slide 24 ash.cs.stevens-tech.edu Domain Names are read from right to left and components separated by a..
25 Domain Names CS615 - Aspects of System Administration Slide 25 ash.cs.stevens-tech.edu. The root is known as., but is usually left out.
26 Domain Names CS615 - Aspects of System Administration Slide 26 ash.cs.stevens-tech.edu. There is a small number of top level domains.
27 Domain Names CS615 - Aspects of System Administration Slide 27 ash.cs.stevens-tech.edu. There is a number of top level domains. wget -O - ftp://rs.internic.net/domain/root.zone \ grep "IN<tab>*NS<tab>" awk {print $1} sort -u wc -l
28 Domain Names CS615 - Aspects of System Administration Slide 28 ash.cs.stevens-tech.edu. Each domain can be divided into any number of sub domains.
29 Domain Names CS615 - Aspects of System Administration Slide 29 ash.cs.stevens-tech.edu. Each domain can be divided into any number of sub domains.
30 Domain Names CS615 - Aspects of System Administration Slide 30 ash.cs.stevens-tech.edu. The left-most component of a domain name may be a hostname.
31 Fully Qualified Domain Names CS615 - Aspects of System Administration Slide 31 ash.cs.stevens-tech.edu. A hostname with a domain name is known as a FQDN.
32 The Original IANA CS615 - Aspects of System Administration Slide 32
33 NIC and Network Solutions CS615 - Aspects of System Administration Slide 33 Before the DNS, the Network Information Center (NIC) at Stanford Research Institute (SRI) allocated domain names. IANA (effectively: Jon Postel) assigned, NIC published. In 1991, this was contracted out to Network Solutions, Inc. (NSI), which held the monopoly on DNS registrations (within.com,.org,.mil,.gov,.edu, and.net) until around 1998.
34 Registries CS615 - Aspects of System Administration Slide 34 IANA manages the root zone (.), arpa.; gtld registries handle gtlds, cctld registries handle cctlds. ICANN accredits domain name registries. Registries may function as a Domain Name Registrar may delegate Domain Name registration control policies of allocations can (and do) censor, revoke, change,... entries (e.g. vb.ly) The domain name space is a tree; if you control one node, you control all the branches and subtrees.
35 DNS servers come in two flavors CS615 - Aspects of System Administration Slide 35 Authoritative Nameservers Recursive Nameservers
36 Hostname resolution CS615 - Aspects of System Administration Slide 36 Resolution on a recursive nameserver (aka resolver) involves a number of queries: $ nslookup ash.cs.stevens-tech.edu Server: Address: #53 Non-authoritative answer: Name: ash.cs.stevens-tech.edu Address: $
37 Hostname resolution CS615 - Aspects of System Administration Slide 37 Resolution on a resolver involves a number of queries: IP panix.netmeister.org > i.root-servers.net.domain: [1au] A? ash.cs.stevens-tech.edu. (52) IP i.root-servers.net.domain > panix.netmeister.org.62105: /8/8 (494) IP panix.netmeister.org > a.gtld-servers.net.domain: [1au] A? ash.cs.stevens-tech.edu. (52) IP a.gtld-servers.net.domain > panix.netmeister.org.53168: /6/3 (609) IP panix.netmeister.org > nrac.stevens-tech.edu.domain: [1au] A? ash.cs.stevens-tech.edu. (52) IP nrac.stevens-tech.edu.domain > panix.netmeister.org.41071: 24322*- 1/2/3 A[ domain]
38 Hostname resolution CS615 - Aspects of System Administration Slide 38 Resolution on a resolver involves a number of queries: $ host -t ns.. name server I.ROOT-SERVERS.NET.. name server D.ROOT-SERVERS.NET.. name server C.ROOT-SERVERS.NET.. name server M.ROOT-SERVERS.NET.. name server F.ROOT-SERVERS.NET.. name server A.ROOT-SERVERS.NET.. name server E.ROOT-SERVERS.NET.. name server L.ROOT-SERVERS.NET.. name server H.ROOT-SERVERS.NET.. name server J.ROOT-SERVERS.NET.. name server B.ROOT-SERVERS.NET.. name server G.ROOT-SERVERS.NET.. name server K.ROOT-SERVERS.NET. $
39 Hostname resolution CS615 - Aspects of System Administration Slide 39 Resolution on a resolver involves a number of queries: $ dig -t ns edu. [...] ;; ANSWER SECTION: edu IN NS l.edu-servers.net. edu IN NS f.edu-servers.net. edu IN NS c.edu-servers.net. edu IN NS g.edu-servers.net. edu IN NS a.edu-servers.net. edu IN NS d.edu-servers.net. ;; ADDITIONAL SECTION: c.edu-servers.net IN A d.edu-servers.net IN A l.edu-servers.net IN A [...] $
40 Hostname resolution CS615 - Aspects of System Administration Slide 40 Resolution on a resolver involves a number of queries: $ -t ns stevens.edu. [...] ;; AUTHORITY SECTION: stevens.edu IN NS nrac.stevens-tech.edu. stevens.edu IN NS sitult.stevens-tech.edu. ;; ADDITIONAL SECTION: nrac.stevens-tech.edu IN A sitult.stevens-tech.edu IN A [...] $
41 Hostname resolution CS615 - Aspects of System Administration Slide 41
42 Hostname resolution CS615 - Aspects of System Administration Slide 42 Resolution on a resolver involves a number of queries: $ nslookup ash.cs.stevens-tech.edu Server: Address: #53 Non-authoritative answer: Name: ash.cs.stevens-tech.edu Address: $
43 Hostname resolution CS615 - Aspects of System Administration Slide 43
44 Hostname resolution CS615 - Aspects of System Administration Slide 44 $ ftp -o - ftp.internic.net:/domain/db.cache more
45 Operation Global Blackout CS615 - Aspects of System Administration Slide 45
46 DNS: A distributed system CS615 - Aspects of System Administration Slide 46 There are 13 root servers.
47 DNS: A distributed system CS615 - Aspects of System Administration Slide 47 There are 13 root servers. Except... there are more.
48 DNS: A distributed system CS615 - Aspects of System Administration Slide 48 There are 13 root authorities.
49 DNS: A distributed system CS615 - Aspects of System Administration Slide 49 There are 13 root server addresses.
50 DNS: A distributed system CS615 - Aspects of System Administration Slide 50 There are hundreds of root servers.
51 DNS: A distributed system CS615 - Aspects of System Administration Slide 51 See e.g.:
52 Operation Global Blackout CS615 - Aspects of System Administration Slide 52
53 DNS: A distributed database CS615 - Aspects of System Administration Slide 53
54 DNS Resource Records CS615 - Aspects of System Administration Slide 54 More than just A and AAAA: CAA certificate authority authorization CNAME the canonical name for an alias MX mail exchange NS an authoritative name server SOA marks the start of a zone of authority SRV service locator (e.g. for kerberos) PTR a domain name pointer TXT text strings...
55 DNS Resource Records CS615 - Aspects of System Administration Slide 55 You ve all seen PTR records: $ host ash.cs.stevens-tech.edu ash.cs.stevens-tech.edu has address ash.cs.stevens-tech.edu mail is handled by 0 guinness.cs.stevens-tech.edu. $ host in-addr.arpa domain name pointer ash.cs.stevens-tech.edu. $ Stevens doesn t have write access to the in-addr.arpa domain. How does this work?
56 Creative uses of DNS Resource Records CS615 - Aspects of System Administration Slide 56 identifying sources of SPAM (via e.g. an RBL) detect spoofing (via e.g. SPF) find out if the internet is on fire: dig +short txt istheinternetonfire.com find ASN numbers by IP addresses: dig +short origin.asn.cymru.com TXT check a resolver s source port randomization (to help mitigate DNS Cache Poisoning attacks): dig +short porttest.dns-oarc.net TXT using DNS to publish SSH key fingerprints (RFC4255, ssh config(5) VerifyHostKeyDNS; for best results combine with DNSSEC)
57 CS615 - Aspects of System Administration Slide 57 Hooray! 5 Minute Break
58 CS615 - Aspects of System Administration Slide 58 Hypertext Transfer Protocol Today s Universal Internet Pipe
59 HTTP: Hypertext CS615 - Aspects of System Administration Slide 59 W W W The World Wide Web is the only thing I know of whose shortened form takes three times longer to say than what it s short for. Douglas Adams
60 HTTP: Hypertext CS615 - Aspects of System Administration Slide 60
61 HTTP CS615 - Aspects of System Administration Slide 61 Hypertext Transfer Protocol RFC2616
62 HTTP CS615 - Aspects of System Administration Slide 62 HTTP is a request/response protocol.
63 The Hypertext Transfer Protocol CS615 - Aspects of System Administration Slide 63 HTTP is a request/response protocol: 1. client sends a request to the server 2. server responds
64 The Hypertext Transfer Protocol CS615 - Aspects of System Administration Slide 64 HTTP is a request/response protocol: 1. client sends a request to the server request method URI protocol version request modifiers client information 2. server responds
65 CS615 - Aspects of System Administration Slide 65 HTTP: A client request $ telnet 80 Trying Connected to Escape character is ^]. GET / HTTP/1.0
66 The Hypertext Transfer Protocol CS615 - Aspects of System Administration Slide 66 HTTP is a request/response protocol: 1. client sends a request to the server request method URI protocol version request modifiers client information 2. server responds status line (including success or error code) server information entity metainformation content
67 HTTP: a server response CS615 - Aspects of System Administration Slide 67 HTTP/ OK Date: Sun, 31 Mar :54:40 GMT Set-Cookie: PREF=ID=c5eb56d629b347cc:FF=0:TM= :LM= : S=sIdRFdxV9YvtQOlG; expires=tue, 31-Mar :54:40 GMT; path=/; domain=.google.com Set-Cookie: NID=67=hvBnOob2NoZW4haTJVfajbcyn_jips50lKRe-8nawzdCZ6AukNR _s8cnhd6za-z2721na3tplrnxt-2zyiui23j4kdsdf8gg--pmgsmoj3jv5frezqg1elhjv92hl-w2; expires=mon, 30-Sep :54:40 GMT; path=/; domain=.google.com; HttpOnly Server: gws <!doctype html><html itemscope="itemscope" itemtype=" <head><meta content="search the...
68 The Hypertext Transfer Protocol CS615 - Aspects of System Administration Slide 68 Server status codes: 1xx Informational; Request received, continuing process 2xx Success; The action was successfully received, understood, and accepted 3xx Redirection; Further action must be taken in order to complete the request 4xx Client Error; The request contains bad syntax or cannot be fulfilled 5xx Server Error; The server failed to fulfill an apparently valid request
69 HTTP: A client request CS615 - Aspects of System Administration Slide 69 $ telnet 80 Trying Connected to Ecape character is ^]. GET / HTTP/1.0 HTTP/ Moved Permanently Date: Mon, 05 Mar :41:06 GMT Server: Apache Location: Vary: Accept-Encoding Content-Length: 235 Connection: close Content-Type: text/html; charset=iso
70 HTTP: A client request CS615 - Aspects of System Administration Slide 70 $ printf "HEAD / HTTP/1.1\r\nHost: openssl s_client -quiet -ign_eof -connect 2>/dev/null HTTP/ Found Date: Mon, 05 Mar :53:38 GMT Server: Apache Location: Vary: Accept-Encoding Content-Type: text/html; charset=iso
71 HTTP: A client request CS615 - Aspects of System Administration Slide 71 $ printf "HEAD /ses/cs HTTP/1.1\r\nHost: openssl s_client -quiet -ign_eof -connect 2>/dev/null HTTP/ Moved Permanently Date: Mon, 05 Mar :54:51 GMT Content-Type: text/html; charset=utf-8 Location:
72 HTTP: A client request CS615 - Aspects of System Administration Slide 72 $ printf "HEAD /schaefer-school-engineering-science/departments/computer-science HTTP/1.1\r\nHost: www openssl s_client -quiet -ign_eof -connect 2>/dev/null HTTP/ OK Date: Mon, 05 Mar :56:37 GMT Content-Type: text/html; charset=utf-8 Connection: keep-alive Expires: Sun, 19 Nov :00:00 GMT Last-Modified: Mon, 05 Mar :44:39 GMT [...]
73 HTTP: A client request CS615 - Aspects of System Administration Slide 73
74 HTTP - more than just text CS615 - Aspects of System Administration Slide 74 HTTP is a Transfer Protocol serving data, not any specific text format. Accept-Encoding client header can specify different formats such as gzip or deflate for compression etc. communications, etc. corresponding server headers: Content-Type and Content-Encoding
75 HTTP - more than just static data CS615 - Aspects of System Administration Slide 75 HTTP is a Transfer Protocol what is transferred need not be static; resources may generate different data to return based on many variables. CGI resource is executed, needs to generate appropriate response headers server-side scripting (ASP, PHP, Perl,...) client-side scripting (JavaScript/ECMAScript/JScript,...) applications based on HTTP, using: AJAX RESTful services JSON, XML, YAML to represent state and abstract information
76 HTTP Proxy Servers CS615 - Aspects of System Administration Slide 76 HTTP traffic usually is very asymmetric a lot of the content is static network ACLs may restrict traffic flow
77 HTTP overload CS615 - Aspects of System Administration Slide 77 Ways to mitigate HTTP overload: DNS round-robin to many web servers load balancing web cache / accelerators (reverse proxies) content delivery networks These solutions depend on the location within the network and the scale of the environment.
78 Load Balancing CS615 - Aspects of System Administration Slide 78
79 Load Balancing: Inbound CS615 - Aspects of System Administration Slide 79
80 Load Balancing: Outbound CS615 - Aspects of System Administration Slide 80
81 Load Balancing: Direct Server Return CS615 - Aspects of System Administration Slide 81
82 Content Delivery Networks CS615 - Aspects of System Administration Slide 82
83 Content Delivery Networks CS615 - Aspects of System Administration Slide 83 cache content in strategic locations determine location to serve from via geomapping of IP addresses (beware IPv6 aggregation!) often uses a separate domain to distinguish small objects/large objects or dynamic content/static content either out-sourced or in-house (if your organization is a Tier-1 or Tier-2 peering partner) request routing happens via Global Server Load Balancing, DNS-based request routing, anycasting etc. provides vast amounts of interesting data about your clients (see
84 CDN Implications CS615 - Aspects of System Administration Slide 84 your CDN sees all your traffic your CDN controls your TLS certificate keys your CDN is a multi-tenant environment your CDN may impose restrictions on your clients separation of cache-able content may require multiple (second-level) domains
85 CS615 - Aspects of System Administration Slide 85 HTTP and DNS Both HTTP and DNS are trivial to set up. Both HTTP and DNS are not trivial to get right.
86 Reading CS615 - Aspects of System Administration Slide 86 HTTP etc.: RFC 2616, 2818, REST: CDNs:
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