Trampoline Routing

Trampoline routing allows a sender with limited routing information to delegate pathfinding to intermediate trampoline nodes. Instead of computing the full route to the destination, the sender only needs a route to the first trampoline node — the rest of the path is handled by the trampoline nodes themselves.

Why Trampoline Routing?

In a standard multi-hop payment, the sender must know the entire network topology to compute a route. This is problematic for:

• Lightweight clients (e.g., mobile wallets) that don't store the full network graph
• Privacy-conscious users who don't want to reveal the full route
• Nodes behind NAT that have limited visibility of the network

How It Works

Sender → [Outer Onion] → First Trampoline → [Inner Onion] → Next Trampoline → ... → Final Recipient

1. The sender builds a normal outer onion to the first trampoline node
2. The remaining route is encoded in an inner trampoline onion
3. Each trampoline node peels one layer of the inner onion and forwards the payment
4. The final recipient sees only the final payload and settles the payment

Using Trampoline Routing

Set trampoline_hops in the send_payment RPC to specify trampoline nodes:

{
  "jsonrpc": "2.0",
  "method": "send_payment",
  "params": [
    {
      "invoice": "fibt1...",
      "trampoline_hops": [
        { "pubkey": "<trampoline_node_1_pubkey>" },
        { "pubkey": "<trampoline_node_2_pubkey>" }
      ],
      "max_fee_amount": "0x5F5E100"
    }
  ],
  "id": 1
}

Fee Behavior

• The sender routes to the first trampoline with final_amount + max_fee_amount

• Any fee spent on the outer route reduces what the first trampoline receives

• The remaining fee budget is split evenly across trampoline hops as build_max_fee_amount

• The forwarding fee follows the standard TLC fee formula:

  fee = ⌈(amount_to_forward × fee_rate) / 1,000,000⌉

Constraints

Privacy Benefits

Trampoline routing improves payment privacy because:

• The sender only knows the route to the first trampoline
• Trampoline nodes only know the previous and next hop
• The final recipient cannot see the full route

Related Topics

• Payment Lifecycle — how payments are processed
• P2P Message Protocol — message-level details