1 Chapter 2 (Section 2.5) Application Layer - DNS Computer Networking: A Top Down Approach Featuring the Internet, 5 rd edition. Jim Kurose, Keith Ross

1

Chapter 2 (Section 2.5)Application Layer - DNS

Computer Networking: A Top Down Approach Featuring the Internet, 5rd edition. Jim Kurose, Keith RossAddison-Wesley, July 2009. Textbook for ECE3076.

A note on the use of these ppt slides:We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!) If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.

Thanks and enjoy! JFK/KWR

All material copyright 1996-2009J.F Kurose and K.W. Ross, All Rights Reserved

Modified for GT ECE6612by Prof. John Copeland

2/25/13

06a DNS.ppt

2

DNS: Domain Name System

People: many identifiers: SSN, name, passport #

Internet hosts, routers: IP address (32 bit) -

used for addressing datagrams

“name”, e.g., www.yahoo.com - used by humans

Q: map between IP addresses and name ?

Domain Name System: distributed database

implemented in hierarchy of many name servers

application-layer protocol host, routers, name servers to communicate to resolve names (address/name translation) note: core Internet

function, implemented as application-layer protocol

complexity at network’s “edge”

06a DNS.ppt

3

DNS

DNS is Hierarchical

Why not centralize DNS? single point of failure traffic volume distant centralized

database maintenance

doesn’t scale!

DNS services Hostname to IP

address translation Host aliasing

Canonical and alias names

Mail server aliasing Load distribution

Replicated Web servers: set of IP addresses for one canonical name

06a DNS.ppt

4

Root DNS Servers

com DNS servers org DNS servers edu DNS servers

poly.eduDNS servers

umass.eduDNS servers

yahoo.comDNS servers

amazon.comDNS servers

pbs.orgDNS servers

Distributed, Hierarchical Database

Client wants IP for www.amazon.com; 1st approx: Client queries a root server to find “com” DNS

server Client queries com DNS server to get

“amazon.com” Authoritative DNS server Client queries amazon.com DNS server to get

IP address for “www.amazon.com”

06a DNS.ppt

5

DNS: Root name servers

contacted by local name server that can not resolve Top_Level name (eats in www.macdonalds.eats)

Originally there were 7 Top-Level domains (com, org, edu, mil, gov, info, arpa) Now there are hundreds ( us, uk, cn, tv, name, ...)

ICANN assigns domain names (www.icann.org)

13 root name servers worldwideb USC-ISI Marina del Rey, CA

l ICANN Los Angeles, CA

e NASA Mt View, CAf Internet Software C. Palo Alto, CA (and 17 other locations)

i Autonomica, Stockholm (plus 3 other locations)

k RIPE London (also Amsterdam, Frankfurt)

m WIDE Tokyo

a Verisign, Dulles, VAc Cogent, Herndon, VA (also Los Angeles)d U Maryland College Park, MDg US DoD Vienna, VAh ARL Aberdeen, MDj Verisign, ( 11 locations)

06a DNS.ppt

6

TLD and Authoritative Servers Top-level domain (TLD) servers: responsible for com, org, net,

edu, etc, and all top-level country domains uk, fr, ca, jp. Network Solutions, Inc. maintains servers for com TLD Educause maintains servers for edu TLD [2007 - TLD servers share responsibilities]

Authoritative DNS servers: organization’s DNS servers, providing authoritative hostname to IP mappings for organization’s servers (e.g., Web and mail). Can be maintained by organization or service provider Every “Autonomous System” (AS) must have two

(backup). Local DNS servers: organization’s DNS servers located on various

subnets to provide DNS lookups for hosts on the subnet. May not be accessible from outside the subnet. Their IP addresses are part of the host's network configuration (manual or DHCP).

PC looks first at “hosts” file. DNS Hack #0, add false info to it.

7

Local Name Server Does not strictly belong to hierarchy Each ISP (residential ISP, company,

university) has one. Also called “default name server” or

“resolver” When a host makes a DNS query, query is

sent to its local DNS server Acts as a proxy, forwards query into hierarchy. Today a DNS proxy (resolver) is built into most

DSL and cable-modem routers

06a DNS.ppt

DNS Hack #1: Change DNS configured IP to IP of attacker-controlled server (Windows Registry or UNIX /etc/resolv.conf)

06a DNS.ppt 8

requesting hostcis.poly.edu

gaia.cs.umass.edu

root DNS server

local DNS serverdns.poly.edu

1

23

4

5

6

authoritative DNS serverdns.cs.umass.edu

78

TLD DNS server

Example

$ nslookup gaia.cs.umass.edu answer 128.119.245.12

Host at cis.poly.edu wants IP address for gaia.cs.umass.edu

Host sends a "recursion-requested" query request to dns.poly.edu.

[Host is doing a non-recursive search]

Local DNS server does a "recursive" search. This requires contacting several other DNS servers before the final answer is given to host.

06a DNS.ppt 9


gaia.cs.umass.edu

root DNS serverA3.NSLTD.COM


1

2

4

5

6

authoritative DNS server

NS1.umass.edu3

Non-recursive queries norecurse or

"iterated" query: contacted server

replies with name of server to contact

“I don’t know this name, but ask this server”

$ nslookup -norecurse -v gaia.cs.umass.edu$ nslookup -norecurse -v gaia.cs.umass.edu A3.NSLTD.COM $ nslookup -norecurse -v gaia.cs.umass.edu NS1.umass.com answer 128.119.245.12

copeland$ dig +trace www.google.com. (may have to do from ecelinsrva.ece)

; <<>> DiG 9.8.3-P1 <<>> +trace www.google.com.;; global options: +cmd. 495753 IN NS e.root-servers.net.. 495753 IN NS c.root-servers.net.. 495753 IN NS a.root-servers.net. . . . (11 lines deleted);; Received 496 bytes from 128.61.244.254#53(128.61.244.254) in 13 ms . . .com. 172800 IN NS h.gtld-servers.net.com. 172800 IN NS j.gtld-servers.net.com. 172800 IN NS e.gtld-servers.net.. . . (11 lines deleted); Received 504 bytes from 192.58.128.30#53(192.58.128.30) in 138 ms

google.com. 172800 IN NS ns2.google.com.google.com. 172800 IN NS ns1.google.com.google.com. 172800 IN NS ns3.google.com.google.com. 172800 IN NS ns4.google.com.;; Received 168 bytes from 192.55.83.30#53(192.55.83.30) in 56 ms

www.google.com. 300 IN A 74.125.196.104www.google.com. 300 IN A 74.125.196.105 . . . (4 lines deleted);; Received 128 bytes from 216.239.36.10#53(216.239.36.10) in 64 ms

“dig” with “+trace” will show the entire recursive lookup.

10

06a DNS.ppt 11

DNS: caching and updating records once (any) name server learns a mapping, it

caches the mapping (Domain’s DNS = IP) cache entries timeout (disappear) after

some time (usually 20 minutes) TLD servers typically cached longer in

local name servers• Thus root name servers not often visited

update/notify mechanisms under design by IETF RFC 2136 http://www.ietf.org/html.charters/dnsind-charter.html

DNS Hack #0: Add a “name -> IP” entry in the UNIX /etc/hosts file, or Windows Registry file.

06a DNS.ppt 12

DNS records

DNS: distributed db storing resource records (RR)

Type=NS name is domain (e.g.

foo.com) value is hostname of

authoritative name server for this domain

RR format: (name, value, type, ttl)

Type=A (AAAA for IPv6) name is hostname value is IP address

Type=CNAME name is alias name for some

“canonical” (the real) name www.ibm.com is really servereast.backup2.ibm.com value is canonical name

Type=MX value is name of

mailserver associated with name

06a DNS.ppt 13

DNS protocol, messagesDNS protocol : query and reply messages, both with same message format

msg header identification: 16 bit #

for query, reply to query uses same #

flags: query or reply recursion desired recursion available reply is authoritative

14

DNS protocol, messages

Name, type fields for a query

RRs in responseto query

records forauthoritative servers

additional “helpful”info that may be used

*

06a DNS.ppt 15

Inserting records into DNS Example: just created startup “Network Utopia” Register name networkuptopia.com at a registrar

(e.g., Network Solutions) Need to provide registrar with names and IP addresses of

your authoritative name server (primary and secondary) Registrar inserts two RRs into the .com TLD server:

(networkutopia.com, dns1.acme.com, NS)(dns1.acme.com, 212.212.212.1, A)

Put in authoritative server Type A record for www.networkuptopia.com and Type MX record for networkutopia.com into dns1.acme.com (DNS service)

DNS Hack #2 Register a domain like “myserver.ru”, have links in email like “www.usbank.com.273846.myserver.ru”.This can hide the real domain. A unique subnet can id the local resolver, and email recipient or Web page viewer.

>dig anyhost.nt.com +norecurse -q=any ; NO NS SPECIFIED

; <<>> DiG 8.3 <<>> anyhost.nt.com +norecurse -q=any ;; res options: init defnam dnsrch;; got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 11306;; flags: qr ra; QUERY: 1, ANSWER: 0, AUTHORITY: 7, ADDITIONAL: 0;; QUERY SECTION:;; anyhost.nt.com, type = A, class = IN

;; AUTHORITY SECTION:IN SOA a.root-servers.net. nstld.verisign-grs.com. 2013022500 1800 900 604800 86400 SOA = Start of Authority Final Dot = Authoritative A.ROOT-SERVERS.NET. <- SPECIFY DNS NEXT TIME

;; Total query time: 4 msec;; FROM: bigzilla.ece.gatech.edu to SERVER: default -- 130.207.230.5;; WHEN: Fri Feb 20 08:00:38 2009;; MSG SIZE sent: 28 rcvd: 156

16

>dig @C.ROOT-SERVERS.NET nt.com. +norecurse ; SPECIFY NAME SERVER

; <<>> DiG 8.3 <<>> @C.ROOT-SERVERS.NET nt.com. +norecurse; (1 server found);; res options: init defnam dnsrch;; got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 26071;; flags: qr; QUERY: 1, ANSWER: 0, AUTHORITY: 13, ADDITIONAL: 15;; QUERY SECTION:;; nt.com, type = A, class = IN

;; AUTHORITY SECTION:com. 2D IN NS C.GTLD-SERVERS.NET. {TOP-LEVEL NS for .com}com. 2D IN NS L.GTLD-SERVERS.NET.com. 2D IN NS A.GTLD-SERVERS.NET.…;; ADDITIONAL SECTION:A.GTLD-SERVERS.NET. 2D IN A 192.5.6.30A.GTLD-SERVERS.NET. 2D IN AAAA 2001:503:a83e::2:30B.GTLD-SERVERS.NET. 2D IN A 192.33.14.30B.GTLD-SERVERS.NET. 2D IN AAAA 2001:503:231d::2:30•••

;; Total query time: 23 msec;; FROM: bigzilla.ece.gatech.edu to SERVER: C.ROOT-SERVERS.NET 192.33.4.12;; WHEN: Fri Feb 20 08:06:09 2009;; MSG SIZE sent: 24 rcvd: 512

17

>dig @192.5.6.30 nt.com. +norecurse -q=any

; <<>> DiG 8.3 <<>> @192.5.6.30 nt.com. +norecurse -q=any ; (1 server found);; res options: init defnam dnsrch;; got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 24266;; flags: qr; QUERY: 1, ANSWER: 0, AUTHORITY: 5, ADDITIONAL: 5;; QUERY SECTION:;; nt.com, type = A, class = IN

;; AUTHORITY SECTION: {Authoritative Name Servers for domain nt.com}nt.com. 2D IN NS ns-guy2.nortelnetworks.com.nt.com. 2D IN NS ns-har2.nortelnetworks.com. •••;; ADDITIONAL SECTION:ns-guy2.nortelnetworks.com. 2D IN A 47.237.0.21ns-har2.nortelnetworks.com. 2D IN A 47.251.0.21•••;; Total query time: 58 msec;; FROM: bigzilla.ece.gatech.edu to SERVER: 192.5.6.30 192.5.6.30;; WHEN: Fri Feb 20 08:07:40 2009;; MSG SIZE sent: 24 rcvd: 229-------------------------------------------------Next: dig @47.237.0.21 anyhost.nt.com. +norecurse -q=any 18

>whois nt.com

Whois Server Version 2.0

Domain names in the .com and .net domains can now be registeredwith many different competing registrars. Go to http://www.internic.netfor detailed information.

Domain Name: NT.COM Registrar: GODADDY.COM, INC. Whois Server: whois.godaddy.com Referral URL: http://registrar.godaddy.com Name Server: NS-GUY2.NORTELNETWORKS.COM Name Server: NS-HAR2.NORTELNETWORKS.COM Status: clientDeleteProhibited Status: clientRenewProhibited Status: clientTransferProhibited Status: clientUpdateProhibited Updated Date: 20-jan-2009 Creation Date: 28-sep-1990 Expiration Date: 27-sep-2010

>>> Last update of whois database: Fri, 20 Feb 2009 13:33:26 UTC <<<

19


IP = 12.34.56.78

www.bigbank.com33.22.11.44

root DNS server


1 Spoofed Request for no.bigbank.com source IP = 12.34.56.78

2 Spoofed Response - source IP = 87.65.43.21Auth. DNS for bigbank.com =66.66.66.66

3

4

5

authoritative DNS server

dns.bigbank.com

8

TLD DNS server - IP = 87.65.43.21

www.bigbank.phisher.com66.66.66.66

Future requests for all URLs in bigbank.com go to =66.66.66.66

DNS Cache Poisoning

20

wireshark Display of DNS Response

ID is random nonceused to authenticateResponse to Query

21

06a DNS.ppt

DNS protocol, spoofed messages

Name, type fields for a query

RRs in responseto query

records forauthoritative servers

additional “helpful”info that may be used

*

* 16-bit ID is used to match responses to requests. To spoof, •use 1 request and 65,536 responses, or •use 256 requests and 256 responses (Birthday attack).

<- 32 bits ->

22

Local DNS NS-CNN.COM Hacker

TimeLookup www.cnn.com

www.cnn.com is 66.66.66.66










www.cnn.com is 66.66.66.66UDP Connection closed ->

66.66.66.66 cached

www.cnn.com -> 64.236.90.21(not noticed)

Correct guess of<- ID Nonce

Probable no. of hits= N / 65,354

DNS Cache Poisoning - Anticipated Attack

23

Sends a Request for a URL,and N fake Replieswith random IDs


Local DNS NS-CNN.COM Hacker

TimeLookup www.cnn.com


www..cnn.com is 66.66.66.66








Local DNS ->

caches www.cnn.com

=66.66.66.66

DNS Cache Poisoning – Bellovin Birthday Attack

24


<- Correct guess of one ID. Probable no. of hits260*N/(2^16)=1 if N =252 Prob(hits>0)=0.63Total packets = 512

<- Sending 260requests for same domain, cnn.com,and N Replieswith fake Auth. N.S. IP address.with random IDs

DNS Hack #3: Change DNS IP configured in local cache.

DOS Attack

* Local DNS sends 260 queries with different IDs.

*

Fast-Flux DNS (Botnet Distributed Phishing)•Botmaster registers his DNS server, with the “ru” TLD (Top Level DNS) as the Authority for “bg4589.ru”

•Botnet hosts sent out email to lure victims to a Phishing Web site www.bny.com.bg4589.ru (IP 23.45.67.89 )

•Problem: as soon as BNY Network Security person sees one of the emails, they do a DNS lookup (get 23.45.67.89), a “whois”, and shut the 23.45.67.89 host down.

•Solution: vary the IP address returned to one of a thousand botnet Web servers.

•Problem: BNY NetSec repeatedly does DNS lookups to get a complete list of botnet hosts.

•Solution: After several lookups from the same IP, have many other bots do a Distributed Denial of Service attack (DDoS) for several days against BNY NetSec.

25DNS Hack #4: Use a Fast Flux DNS to prevent total shutdown.

06a DNS.ppt 26

requesting hostjoe.poly.edu

root DNS server


1

23

4

5

6

authoritative DNS serverdns.urhcked.com

78

TLD DNS server

Fast Flux DNSURL in Phish -> One of Many bots

$ nslookup www.urhckd.com. answer 78.82.245.12

Host at poly.edu wants IP address for www.urhckd.com

Host sends a "recursion-requested" query request to dns.poly.edu.

[Host is doing a non-recursive search]

Local DNS server does a "recursive" search. This requires contacting several other DNS servers before the final answer is given to host.

Fast Flux - many IP’s of bot Phishing sites.

Adapted from “Computer Networking: A Top Down Approach Featuring the Internet”, by Jim Kurose & Keith Ross

$ nslookup www.urhckd.com. answer 53.119.24.124

Note: the dot after "com" below is necessary to avoid getting the same cached answer from dns.poly.edu.

New Protocols supplement DNS and DHCP on LAN

* In addition to network configuration (DHCP) and Name Resolution (DNS), it’s nice to have a list of servers available on your LAN. For example, be able to select from a list of printers.

•Link-Local: Rather than initially using the Network IP Address (host bits 0), randomly select one of 65,534 addresses in 169.254.x.x/16 (you don’t have to know the network address).

•Apple’s mDNS (UDP port 5353) is an open specification that lets a host announce a chosen Name (e.g., “Lab Printer”) in a multicast message to 224.0.0.251). Hosts running mDNS will all listen to this multicast address and add “Lab Printer” and its IP address and MAC address to the list of servers available. DNS-SD advertises Server Names and services.

•Microsoft’s NetBios Name Service (NBNS) is similar, but uses the Network Broadcast Address (host bits all 1). UPnP protocol Simple Service Delivery (SSDP) advertises services.

•The IETF is developing a similar Internet standard - Service Location Protocol (SLP).

en.wikipedia.org/wiki/MDNS 2/26/10 27

DNSSEC – DNS Security Extensions

en.wikipedia.org/wiki/DNSSEC 2/26/13 28

DNSSEC works by digitally signing records for DNS lookup using public-key cryptography. The correct DNSKEY record is authenticated via a chain of trust, starting with a set of verified public keys for the DNS root zone which is the trusted third party.

New DNS record types were created or adapted to use with DNSSEC: RRSIG, DNSKEY, DS, NSEC, NSEC3, NSEC3PARAM.

When DNSSEC is used, each answer to a DNS lookup will contain an RRSIG DNS record, in addition to the record type that was requested. The RRSIG record is a digital signature of the answer DNS resource record set. The digital signature can be verified by locating the correct public key found in a DNSKEY record.

Stub resolvers (host software) are "minimal DNS resolvers that use recursive query mode to offload most of the work to a recursive name server.”

A validating stub resolver can also potentially perform its own signature validation by setting the Checking Disabled (CD) bit in its query messages, for end-to-end DNS security for domains implementing DNSSEC.

Reverse DNS Lookups

en.wikipedia.org/wiki/DNSSEC 2/26/13 29

Reverse DNS Lookups (e.g., nslookup 130.207.225.101)

> nslookup 130.207.225.101

101.225.207.130.in-addr.arpa name = seiya.ece.gatech.edu.

The “arpa” top-level domain is now only used for reverse lookups. ARPA has been redefined as standing for “Address and Routing Parameter Area.”

For looking up a IPv4 address, the dotted-decimal text string is reversed, and the domain name “in-addr.arpa” is added. Like normal name lookups, the recursion proceeds from right to left. If the block of addresses 130.207.0.0/16 are assigned to the Autonomous System (AS) gatech.edu, then Georgia Tech (OIT) is responsible for maintaining a database for x.y.207.130 (addresses 130.207.0.0 to 130.207.255.255).

The domain for IPv6 addresses is ip6.arpa.

dig www.ece.gatech.edu [ MX records not shown]; <<>> DiG 9.6-ESV-R4-P3 <<>> www.ece.gatech.edu;; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 56886;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 5;; QUESTION SECTION:;www.ece.gatech.edu. IN A;; ANSWER SECTION:www.ece.gatech.edu. 28800 IN A 130.207.225.101;; AUTHORITY SECTION:ece.gatech.edu. 28800 IN NS dns1.gatech.edu.ece.gatech.edu. 28800 IN NS dns3.gatech.edu.;; ADDITIONAL SECTION:dns1.gatech.edu. 28800 IN A 128.61.244.253dns1.gatech.edu. 28800 IN AAAA 2610:148:1f00:f400::3dns3.gatech.edu. 28800 IN A 168.24.2.35;; Query time: 37 msec;; SERVER: 192.168.1.1#53(192.168.1.1) {note: mail handlers (MTAs) not shown.};; WHEN: Mon Feb 25 12:50:39 2013;; MSG SIZE rcvd: 213

30

nslookup -q=ANY gatech.edu {note: use domain name only, for MX info}Server: 192.168.1.1Address: 192.168.1.1#53

gatech.eduorigin = brahma5.dns.gatech.edumail addr = hostmaster.gatech.eduserial = 380555175refresh = 10800retry = 3600expire = 2592000minimum = 60

Name: gatech.eduAddress: 130.207.160.29gatech.edu nameserver = dns1.gatech.edu.gatech.edu nameserver = heath.dpo.uab.edu. {Backup DNS at U. Alabama}gatech.edu nameserver = dns3.gatech.edu.gatech.edu nameserver = dns2.gatech.edu.gatech.edu mail exchanger = 10 mx1.gatech.edu.gatech.edu mail exchanger = 10 mx2.gatech.edu.gatech.edu text = "MS=ms45592394"gatech.edu text = "MS=ms74949178" 31

Documents

1 Chapter 2 (Section 2.5) Application Layer - DNS Computer Networking: A Top Down Approach Featuring the Internet, 5 rd edition. Jim Kurose, Keith Ross