SIP ALG | Junos OS

Publisher

Juniper Networks

URL

https://www.juniper.net/documentation/us/en/software/junos/alg/topics/topic-map/security-sip-alg.html

Published

unknown

Updated

unknown

Accessed

2026-09-25

HTTP status

200

License

Juniper copyright; all rights reserved; no-redistribution; short excerpts and locators only

Source notes citing this source

• An ALG can be detected by capturing the same SIP message on both sides of the NAT device. If Via, Contact, Record-Route or the SDP c= and m= values differ between the two captures, the device has rewritten the SIP payload, beyond translating the IP and UDP headers. inferred in context
• Juniper's SIP ALG topic page states that the SIP ALG is disabled by default on SRX devices and enabled by default on other devices. disputed in context
• The Junos SIP ALG monitors SIP transactions and dynamically creates pinholes for RTP and RTCP, based on the addresses and ports it extracts from the SDP. in context
• Juniper documents that the Junos SIP ALG modifies the Via, Contact, Route and Record-Route headers and the SDP c= and m= fields. in context
• On Junos OS, show security alg status in operational mode shows whether the SIP ALG is enabled. in context
• One-way or no audio is a plausible result of an ALG that rewrites the SDP c= or m= values incorrectly, or opens RTP pinholes for the wrong address or port. The far end then sends RTP to a destination that does not reach the phone. inferred in context

Cite this source record

APA

WarmTransfer. (2026, September 25). SIP ALG | Junos OS. WarmTransfer. https://warmtransfer.net/knowledge/sources/juniper-junos-sip-alg-topic

BibTeX

@misc{warmtransfer-juniper-junos-sip-alg-topic,
  title  = {SIP ALG | Junos OS},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/sources/juniper-junos-sip-alg-topic},
  note   = {Juniper Networks, accessed 2026-09-25}
}