Hi, First of all I'm sorry if this not a really good place to ask, but I spotted very strange behavior using Linphone and Freeswitch. I'm not sure that this is 100% Freeswitch bug, but maybe you point me to proper direction. Test environment: Linphone =SRTP==> Freeswitch =SRTP==> 2nd Linphone Linphone & 2nd Linphone located behind NAT in same private network. 1) This invite is sent from Linphone to Freeswitch: I left only SDP part where all ciphers are listed(same I did for all other sip packages) a=crypto:1 AES_CM_128_HMAC_SHA1_80 inline:2QEye591aHIqRwdLODMrr8ieQBBHl5WdIizE0NH2. a=crypto:2 AES_CM_128_HMAC_SHA1_32 inline:d6K8m+tGEMvkEbRm5Zzy6KQkrlwS78l7wGufgx8S. a=crypto:3 AES_CM_256_HMAC_SHA1_80 inline:PMvGinW3fpIejXOWDskUNWUhBX1KRlhrPkbrP0Nv4L/+My1V7w2r/ALSyLhkPg==. a=crypto:4 AES_CM_256_HMAC_SHA1_32 inline:ZsdwMe0D+RauGydaQ90qG7pfOvdW6m9cxjbBhJ5AUaNSTecse9Sk3lRzlgZuSA==. 2) Trying from Freeswitch 3) Freeswitch replies Proxy Authentication Required 4) ACK from Linphone 5) Linphone sends one more invite to Freeswitch: a=crypto:1 AES_CM_128_HMAC_SHA1_80 inline:2QEye591aHIqRwdLODMrr8ieQBBHl5WdIizE0NH2. a=crypto:2 AES_CM_128_HMAC_SHA1_32 inline:d6K8m+tGEMvkEbRm5Zzy6KQkrlwS *As we can see this is something very strange, cause Linphone first invite send 4 ciphers, but now it sends only 2 and it looks like that second one is missing something.* 6) Trying from freeswitch 7) Invite sent from Freeswitch to 2nd Linphone a=crypto:1 AEAD_AES_256_GCM_8 inline:jotCMStRYMvwWT18wMqmgwAu6mVBKaIkENGh8HLF0UYFEcwGnoQpM0m4juU. a=crypto:2 AEAD_AES_128_G And as we can see in Invite from Freeswitch to 2nd Linphone ciphers are completely different from what Linphone sent in second Invite. I think this is not 100% Linphone bug. What you think? Full sip trace you can find in attachemnt, additionnally I will rase same issue on Linphone side. With kind regards, Jurijs