Working with large SIP packets

Publisher

Cisco Systems

URL

https://www.cisco.com/c/en/us/support/docs/unified-communications/broadworks/216690-working-with-large-sip-packets.html

Published

2020-11-11

Updated

unknown

Accessed

2026-10-02

HTTP status

200

License

Cisco documentation terms; no-redistribution; short excerpts and locators only

Source notes citing this source

• Cisco's BroadWorks tech note says routers commonly block fragmented UDP because they must buffer fragments until the whole message arrives, which attackers can exploit to exhaust memory. in context
• In Cisco BroadWorks, the Application Server parameter supportTcp under AS_CLI/Interface/SIP enables TCP for SIP. in context
• Cisco BroadWorks handles large SIP messages by switching them to TCP rather than relying on UDP fragmentation, with transport settable per interface, network server, media server and routing NE as UDP, TCP or unspecified. in context
• Cisco's BroadWorks note states Polycom phones can be set to TCPOnly, TCPpreferred or DNSnaptr transport so large SIP messages avoid UDP. in context
• Moving SIP signalling from UDP to TCP or TLS removes dependence on IP fragmentation for large messages because TCP segments data to the negotiated MSS, which is why vendors give it as the primary fix. inferred in context

Cite this source record

APA

WarmTransfer. (2020, November 11). Working with large SIP packets. WarmTransfer. https://warmtransfer.net/knowledge/sources/cisco-broadworks-216690-large-sip-packets

BibTeX

@misc{warmtransfer-cisco-broadworks-216690-large-sip-packets,
  title  = {Working with large SIP packets},
  author = {{WarmTransfer}},
  year   = {2020},
  url    = {https://warmtransfer.net/knowledge/sources/cisco-broadworks-216690-large-sip-packets},
  note   = {Cisco Systems, accessed 2026-10-02}
}