TTL

TTL rewriting sets IPv4 Time To Live to a fixed value.

yaml

l3-rewrite:
  ttl: true
  ttl-value: 128

ttl-value accepts values from 1 to 255 and defaults to 64. It can also be set with the --l3-rewrite-ttl-value command-line flag or the UA3F_L3_REWRITE_TTL_VALUE environment variable. The netfilter and eBPF acceleration paths use the same target value.

TTL rewriting is useful when the gateway should normalize outgoing packet TTL values.

When using the netfilter path with software flow offload enabled, ttl-value: 255 cannot guarantee an outgoing TTL of 255. UA3F sets the ingress TTL to the target value plus one to compensate for the forwarding decrement, but IPv4 TTL is limited to 255 and cannot be set to 256. As a result, forwarded packets on the offload path leave with TTL 254, while packets on the normal POSTROUTING path still leave with TTL 255. Disable flow offload if all outgoing packets must have TTL 255.

TTL ​

TTL