smom-dbis-138/docs/deployment/CCIP_BRIDGE_DESTINATIONS_AND_LINK_FUNDING.md

CCIP Bridge Destinations and LINK Funding

This document describes how to configure addDestination on each CCIP WETH9/WETH10 bridge and how to fund bridges with LINK for cross-chain fees. Use it after deploying bridges via deploy-all-mainnets-with-mapper-oracle-pmm.sh ccip (or DeployAll per chain).

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1. Overview

• Each CCIPWETH9Bridge and CCIPWETH10Bridge must have destination chains set via addDestination(uint64 chainSelector, address receiverBridge).
• Only the bridge admin can call addDestination. Use the same deployer key (or the key that owns admin) when running scripts.
• For each pair of chains (e.g. Ethereum ↔ Chain 138), you add the destination chain selector and the receiver bridge address on the other chain.
• CCIP fees can be paid in LINK (or native token depending on contract). Ensure each bridge contract has enough LINK (and/or native) to pay for ccipSend fees.

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2. Chain Selectors and .env Bridge Variables

Use these from .env (or Chainlink CCIP Supported Networks):

Chain	Chain ID	Selector (.env)	WETH9 Bridge (.env)	WETH10 Bridge (.env)
Ethereum	1	ETH_MAINNET_SELECTOR	MAINNET_CCIP_WETH9_BRIDGE	MAINNET_CCIP_WETH10_BRIDGE
BSC	56	BSC_SELECTOR	CCIPWETH9_BRIDGE_BSC	CCIPWETH10_BRIDGE_BSC
Polygon	137	POLYGON_SELECTOR	CCIPWETH9_BRIDGE_POLYGON	CCIPWETH10_BRIDGE_POLYGON
Arbitrum	42161	ARBITRUM_SELECTOR	CCIPWETH9_BRIDGE_ARBITRUM	CCIPWETH10_BRIDGE_ARBITRUM
Optimism	10	OPTIMISM_SELECTOR	CCIPWETH9_BRIDGE_OPTIMISM	CCIPWETH10_BRIDGE_OPTIMISM
Avalanche	43114	AVALANCHE_SELECTOR	CCIPWETH9_BRIDGE_AVALANCHE	(set if deployed)
Cronos	25	CRONOS_SELECTOR	CCIPWETH9_BRIDGE_CRONOS	CCIPWETH10_BRIDGE_CRONOS
Base	8453	BASE_SELECTOR	CCIPWETH9_BRIDGE_BASE	CCIPWETH10_BRIDGE_BASE
Gnosis	100	GNOSIS_SELECTOR	CCIPWETH9_BRIDGE_GNOSIS	CCIPWETH10_BRIDGE_GNOSIS
Chain 138	138	CHAIN138_SELECTOR (if set)	CCIPWETH9_BRIDGE_CHAIN138	CCIPWETH10_BRIDGE_CHAIN138

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3. Adding Destinations (addDestination)

For each bridge, call:

bridge.addDestination(destinationChainSelector, receiverBridgeAddress);

• destinationChainSelector: the selector of the destination chain (e.g. Ethereum’s selector when configuring “this chain → Ethereum”).
• receiverBridgeAddress: the address of the same type of bridge (WETH9 or WETH10) on the destination chain.

Example: On Ethereum WETH9 bridge, to allow transfers to Chain 138:

# From smom-dbis-138, with .env loaded
cast send "$MAINNET_CCIP_WETH9_BRIDGE" "addDestination(uint64,address)" "$CHAIN138_SELECTOR" "$CCIPWETH9_BRIDGE_CHAIN138" \
  --rpc-url "$ETHEREUM_MAINNET_RPC" --private-key "$PRIVATE_KEY"

Example: On Chain 138 WETH9 bridge, to allow transfers to Ethereum:

cast send "$CCIPWETH9_BRIDGE_CHAIN138" "addDestination(uint64,address)" "$ETH_MAINNET_SELECTOR" "$MAINNET_CCIP_WETH9_BRIDGE" \
  --rpc-url "$RPC_URL_138" --private-key "$PRIVATE_KEY" --legacy

Using the existing script (Ethereum mainnet)

For Ethereum WETH9/WETH10 bridges, you can use:

# From repo root, with .env loaded
scripts/ccip/ccip-configure-destination.sh --token weth9 --action add --selector <DEST_CHAIN_SELECTOR> --receiver <RECEIVER_BRIDGE_ADDR> --pk "$PRIVATE_KEY" --rpc "$ETHEREUM_MAINNET_RPC"
scripts/ccip/ccip-configure-destination.sh --token weth10 --action add --selector <DEST_CHAIN_SELECTOR> --receiver <RECEIVER_BRIDGE_ADDR> --pk "$PRIVATE_KEY" --rpc "$ETHEREUM_MAINNET_RPC"

Repeat for each destination chain (BSC, Polygon, Base, Optimism, Avalanche, Cronos, Gnosis, Chain 138) using the correct selector and the corresponding bridge address on that chain.

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4. LINK Funding and Activation Scope

• CCIP charges fees for each cross-chain message; bridges typically pay in LINK (or native) depending on the contract’s feeToken and ccipSend usage.
• Per chain: Ensure the bridge contract holds enough LINK (and native for gas) so it can pay CCIP fees when users call sendCrossChain (or equivalent).
• Important distinction:
  • Destination-only receipt on a chain does not by itself require LINK on that chain's bridge contract, because ccipReceive(...) does not pay the CCIP fee.
  • Outbound sending from a chain does require a fee payment path on that chain's bridge contract.
• Current WEMIX nuance:
  • CCIPWETH9Bridge may be configured for native-fee mode by setting feeToken = address(0).
  • CCIPWETH10Bridge still requires LINK in the current implementation.
• How to fund:
  1. Get LINK on the same chain as the bridge (e.g. from an exchange or faucet).
  2. Transfer LINK to the bridge contract address (the same address you use for addDestination), or use any approved mechanism (e.g. admin top-up function if the contract has one).
• LINK token addresses per chain are in .env (e.g. CCIP_GNOSIS_LINK_TOKEN, CCIP_ETH_LINK_TOKEN, etc.) and on Chainlink CCIP Supported Networks.
• Script: Run scripts/deployment/fund-ccip-bridges-with-link.sh to send LINK to all CCIP bridges (sources .env; set --link amount, default 10 LINK; use --dry-run to print commands only).

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5. Script: Configure all destinations

From repo root (with .env loaded):

# Step A: Chain 138 → each mainnet (requires RPC_URL_138)
# Step B: Each mainnet → Chain 138 (requires CHAIN138_SELECTOR in .env)
bash scripts/deployment/configure-all-ccip-bridge-destinations.sh

Use --dry-run to print commands only. Step A uses --gas-limit (default 200000) to avoid RPC estimateGas issues on Chain 138; "destination already exists" means that lane is already configured. Step B: optional .env overrides for high-fee chains: BRIDGE_ETH_GAS_PRICE=40000000, BRIDGE_ARBITRUM_GAS_PRICE=25000000, BRIDGE_AVALANCHE_GAS_PRICE=140000000.

6. Checklist (post-deploy)

• Run configure-all-ccip-bridge-destinations.sh (and retry any failed chains).
• For each deployed bridge (WETH9 and WETH10) on each chain, call addDestination for every other chain you want to support (using that chain’s selector and the receiver bridge address).
• Fund each bridge contract with LINK (and native if needed) on its chain.
• Run a small test transfer per lane (e.g. 138 ↔ Ethereum, 138 ↔ BSC) and verify on explorers.

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7. References

• Runbook: docs/deployment/ALL_MAINNETS_DEPLOYMENT_RUNBOOK.md
• Script (Ethereum): scripts/ccip/ccip-configure-destination.sh
• Bridge config (138 ↔ Mainnet): scripts/deployment/configure-bridge-destinations.sh (note: may use different ABI; prefer addDestination(uint64,address) for CCIPWETH9/CCIPWETH10)
• WETH CCIP deployment: docs/operations/integrations/WETH_CCIP_DEPLOYMENT.md