Home / NAT, ICE, and the ALG problem
NAT, ICE, and the ALG problem
Why embedded addresses break, and what rport, STUN, TURN, ICE, SIP ALGs, and media latching each actually do.
7 rooms42 quiz items
Rooms
- Embedded addresses and NAT
SIP and SDP embed IP addresses. NAT rewrites the packet header and leaves those embedded addresses behind.
- rport and symmetric responses
RFC 3581 adds rport so the response is sent to the source address and port the request came from.
- STUN server-reflexive addresses
STUN, RFC 8489, lets a client learn the address a server sees. It obsoletes RFC 5389.
- TURN relays
TURN, RFC 8656, allocates a relay when host and server-reflexive paths fail. It obsoletes RFC 5766.
- ICE candidate types
ICE is RFC 8445, which obsoletes RFC 5245. Candidates are host, srflx, prflx, and relay.
- The SIP ALG problem
A SIP ALG rewrites SIP and SDP in transit and often corrupts the call. It cannot rewrite TLS.
- Media latching on an SBC
Many SBCs learn the remote RTP address from the first packet instead of trusting c=. That is deployment practice, and RFC 5853 is the requirements RFC.
Ecosystem
SIP does not replace workforce management, quality monitoring, CRM, emergency policy, or a messaging registry. It is the session seam those systems hang from. Compliance notes on this page are educational and are not legal advice.