DHCP option for SIP servers

1
DHCP option for SIP servers

• Henning Schulzrinne
• Gautam Nair
• Columbia University

2
Overview

• SIP (RFC 2543) Session Initiation Protocol
• Originally, mainly for setting up multimedia
  conferences and IP telephone calls
• Now also proposed for instant messaging and
  presence (SIMPLE WG)

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SIP servers

• SIP proxy server routes requests
• Typically, found like email server (except via
  DNS SRV, not MX)
• Outbound proxy used for all outbound requests,
  regardless of destination
• For firewall control, policy enforcement, name
  mapping

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How to find the SIP server

• Needs to be configured into client
• Many clients are IP phones -gt automate
• DHCP option

DHCP option
length
Sip.example.com
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Name resolution

• Note this is probably a case that will appear
  more often
• Use SRV lookup for name
• If none, use CNAME/A/AAAA(?) lookup
• Allow dotted-quad (128.59.16.1) as exception
  since users will use it anyway (all applications
  do)

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Considerations

• Needs to work with existing DHCP servers -gt DNS
  string (RFC 1035) \3sip\6foobar\2de not likely to
  be workable, would need new entry type
• Characters are the same as in DNS entries,
  whatever that is exactly (ASCII, currently see
  IDN)

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Summary

• Necessary for deployment of SIP
• Consensus of SIP working group
• May be applicable to other SRV-based lookups
  where numeric IP address is not appropriate
• DHCPv6?