1. RFC 3361: DHCP Option for SIP Servers Speaker: Chung yu Wu Teacher: Quincy Wu

2. CSIE2 Outline Introduction DHCP DNS SIP server DHCP option Security Considerations Conclusion References

3. CSIE3 Introduction This document defines a DHCP option that contain that contains a list of domains or IPv4 address that can be mapped to one or more SIP outbound proxy servers 。

4. CSIE4 Introduction (cont) Outbound SIP request URL SIP request message SIP response message RTP Media stream User agent client User agent server SIP server Outbound proxy server

5. CSIE5 DHCP The Dynamic Host Configuration Protocol is a mechanism for having a DHCP server distribute IP addresses to DHCP client systems on a network 。 Can provide a DHCP client with a full set of TCP/IP configuration values ， such as netmask ， gateway address etc 。

6. CSIE6 Configuration values IP ex:10.10.16.31 netmask ex:255.255.255.0 gateway ex:10.10.16.254 DNS IP ex:163.22.2.1

7. CSIE7 DHCP Operation Find DHCP server  DHCPDISCOVER Offer IP to rent the address  DHCPOFFER Accept IP lease  DHCPREQUEST The lease confirming  DHCPACK

8. CSIE8 DHCP Operation (cont) Ethernet DHCP clientDHCP server 1.DHCPDISCOVER 2.DHCPOFFER 3.DHCPREQUEST 4.DHCPACK

9. CSIE9 DNS DNS is an Internet-wide service that provides mappings between IP addresses and hostnames 。  The DNS is a distributed database implemented in a hierarchy of name servers 。  The DNS is also an application-layer protocol  IP address — a 32 bit identifier used for addressing hosts and routing data to them  Hostname — an ASCII string used by applications

10. CSIE10 DNS (cont) Cache memory DNS server DNS client Search DNS Response DNS root Name server ncnu.edu.tw edu.tw tw hk educom ncnunctu Search www.ncnu.edu.tw Search root Search tw Search edu.tw Search ncnu.edu.tw response

11. CSIE11 SIP server DHCP option SIP server DHCP option has two encoding: 1. encoding byte value ‘enc’=0 list of domain names 2. encoding byte value ‘enc’=1 one or more IPv4 address ‘Len’: the total number of octets in the option, including the encoding byte A DHCP server MUST NOT mix the two encoding in the same DHCP message. The code for this option is 120

12. CSIE12 Domain Name List The DHCP option for this encoding has the following format: Code Len enc DNS name of SIP server 120 N 0 s1 s2 s3 s4 s5

13. CSIE13 Example of Domain Name List Ex: ncnu.edu and ncnu.com 120 21 0 4 “n” “c” “n” u” 3 “e” “d” “u” 0 4 “n” “c” “n” u” 3 “c” “o”“m” 0

14. CSIE14 IPv4 Address List The DHCP option for this encoding has the following format:  Minimum length is 5  The length MUST be a multiple of 4 plus one 120 n 1 a1 a2 a3 a4 a1……….. Code Len enc Address 1 Address 2

15. CSIE15 Example of IPv4 Address List 120 5 1 a3 16 10 21 Display the address

16. CSIE16 Security Considerations Modify the response from a DHCP server SIP user agent could be led to contact a rogue SIP server ， possibly one that then intercepts call requests or denies service 。

17. CSIE17 Conclusion Defines DHCP option: -List of domain names -IPv4 address Can be mapped to one or more SIP outbound proxy servers

18. CSIE18 References RFC 2131 Dynamic Host Configuration Protocol RFC3261 Session Initiation Protocol RFC2119 Key words for use in RFCs to indicate requirement levels