Information about Packet Duplication
Cisco IOS XE Catalyst SD-WAN devices use packet duplication to overcome packet loss.
Packet duplication sends copies of packets on alternate available paths to reach Cisco IOS XE Catalyst SD-WAN devices. If one of the packets is lost, a copy of the packet is forwarded to the server. Receiving Cisco IOS XE Catalyst SD-WAN devices discard copies of the packet and forward one packet to the server.
Packet duplication is suitable for edges with multiple access links. Once packet duplication is configured and pushed to your device, you can see the tunnel packet duplication statistics.
Packet Duplication for Large Packets Using Underlay Fragmentation
When packets are intercepted for duplication, the system queries the IP database using the incoming tunnel ID. It then fetches the duplicate tunnel object. The system compares the packet length with the path maximum transmission unit (PMTU) of the duplicate tunnel. If the packet length is smaller than the duplicate tunnel's PMTU, the packets are duplicated.
Starting from Cisco IOS XE Catalyst SD-WAN Release 17.15.1a, packet duplication with underlay fragmentation ensures that packets get duplicated even when the packet size is more than the PMTU of duplicate tunnel.
For more information on how to enable underlay fragmentation, see VFR and Underlay Fragmentation.
To monitor packet duplication statistics, see View Loss Percentage, Latency, Jitter, Octet, and Packet Duplication Information for Tunnels.
Supported Traffic
Cisco IOS XE Catalyst SD-WAN Devices support packet duplication for the following traffic types:
From Cisco IOS XE Catalyst SD-WAN Release 16.12.1b:
IPv4 traffic over IPv4 tunnel
From Cisco IOS XE Catalyst SD-WAN Release 17.15.1a:
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IPv4 traffic over IPv6 tunnel
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IPv6 traffic over IPv4 tunnel
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IPv6 traffic over IPv6 tunnel