The outbound SIP trunk is dropping calls with a 408 Request Timeout the moment the primary fiber link loses carrier. Edge appliance runs v2.4.1 on a Dell PowerEdge R740 chassis. BIOS sits at 1.12.3 and the iDRAC network adapter shows the secondary 5G NIC taking over without any MAC address conflict. Local media stays alive in survivability mode, which is fine. The problem is the SIP INVITE packets getting stuck at the edge router during the handoff.
Architect flow uses a standard Make Outbound Call block with the SIP trunk connection profile. It works fine on the primary link. Once the failover triggers, the SIP registrar on the Edge reports REGISTRATION_EXPIRED after exactly 95 seconds. The call log shows:
2024-05-12T09:14:22Z SIP/2.0 408 Request Timeout
Via: SIP/2.0/UDP 10.20.4.5:5060;branch=z9hG4bK-12345
From: +81312345678 <sip:+81312345678@edge.local>
To: <sip:+18005550199@trunk.provider.net>
Checked the community posts about MTU fragmentation on Dell NICs during link flaps. Tried dropping the Jumbo Frames setting to 1500 on the secondary interface. Didn’t help. The firewall rules are identical for both WAN ports. Edge pairing stays green in the admin console.
Environment specs:
- Genesys Cloud Edge v2.4.1 (build 2024.03.15)
- Dell R740, BIOS 1.12.3, PERC H755 controller in RAID 1
- Dual WAN: Primary 1Gbps fiber, Secondary 5G LTE modem (USB bonded)
- SIP Trunk: Generic carrier, TLS 1.2, SRTP enabled
- Architect flow: Make Outbound Call → Play Prompt → Transfer to IVR
- OS: Edge Linux custom image, kernel 5.15.0-91
Routing table on the appliance shows the default gateway swapping correctly. But the SIP keepalive packets stop reaching the carrier gateway. Looks like the network stack isn’t flushing the old socket connections fast enough during the NIC handoff. Another post mentioned tweaking the net.ipv4.tcp_retries2 value, but this is UDP traffic. The local media path bypasses the SIP stack completely, which explains why internal calls survive. Firewall is doing jack all on the secondary port.
tcpdump -i eth1 -n port 5060
IP 10.20.4.5.5060 > 203.0.113.45.5060: SIP, length: 482
IP 10.20.4.5.5060 > 203.0.113.45.5060: SIP, length: 482 (retransmit 1)
IP 10.20.4.5.5060 > 203.0.113.45.5060: SIP, length: 482 (retransmit 2)