Symptom
CUBE fails to decrypt SRTP DTMF packets, resulting in DTMF events not recognized by an IVR.
Decryption of SRTP results in DTMF events with "unknown" or with unexpected payloads.
Conditions
Router used as CUBE like ISR4K or CAT8K (pending to define if vCUBE also)
RTP/SRTP interworking. SRTP in affected DTMF leg, using inband RFC2833 method.
IOS-XE 17.6.6a
Using first known affected cipher AES_CM_128_HMAC_SHA1_80
Workaround
Use another cipher in voice-class srtp crypto. Tested AEAD_AES_128_GCM to work.
Use unsecure RTP instead
Downgrade to 17.6.5 or upgrade to 17.9.X
Further Problem Description
