Relay, Repair, and Traffic

In gossip mode, SOF is not observer-only by default.

That is the main reason this page exists.

If that sentence is surprising, go back to Before You Start first. The rest of this guide assumes the difference between direct UDP mode and gossip-bootstrap mode is already clear.

Default Network Posture

When gossip-bootstrap is enabled, SOF can:

  • receive live traffic from the gossip-discovered network
  • relay recent shreds through a bounded cache
  • serve bounded repair responses

This is cluster-participating behavior. Use it because you need it, not because you assume gossip is the premium path.

Control Plane Only

If you only need gossip-derived cluster topology without gossip shred ingest, use:

SOF_GOSSIP_RUNTIME_MODE=control_plane_only

Or in typed runtime setup:

use sof::runtime::{GossipRuntimeMode, RuntimeSetup};

let setup = RuntimeSetup::new()
    .with_gossip_runtime_mode(GossipRuntimeMode::ControlPlaneOnly);

That mode keeps the gossip control plane alive but does not start gossip-backed shred ingest, relay, repair, or runtime switching. It is useful when sof-tx needs topology/leader inputs but your actual data ingress comes from somewhere else. You still need a recent-blockhash source from SOF's other ingest paths, RPC, or your own control plane.

Reduce Outbound Activity

If your goal is to keep ingest while cutting outward network activity, start here:

SOF_UDP_RELAY_ENABLED=false
SOF_REPAIR_ENABLED=false

Before disabling behavior entirely, also consider narrower changes such as:

  • narrowing SOF_GOSSIP_VALIDATORS
  • keeping SOF_UDP_RELAY_REQUIRE_TURBINE_SOURCE_PORTS=true
  • lowering SOF_UDP_RELAY_MAX_SENDS_PER_SEC incrementally

Why Boundedness Matters

Relay and repair are not allowed to grow without limit.

Examples of explicit bounds:

  • relay cache window and maximum retained shreds
  • relay fanout and sends-per-second budgets
  • repair request budgets per tick
  • per-slot repair caps
  • per-peer serve limits and byte budgets

These limits are part of the anti-amplification and hot-path discipline, not just tuning details.

SOF 2026