Which IGP to Use & Understanding Gas Amounts

Two different types of IGP contracts are provided. Read below to understand which one to use and how to use it.
When using the default ISM (for most applications)
If your application makes use of the default Interchain Security Module (ISM) for security by either not specifying a custom ISM or specifying the MultisigIsm, your application can make use of the DefaultIsmInterchainGasPaymaster.
The default ISM is the default security module for Hyperlane messages, so if you don't know if you're using the default ISM for security, then you are automatically using the default ISM.
When using the DefaultIsmInterchainGasPaymaster, the _gasAmount to use when calling the payForGas or quoteGasPayment functions only needs to be the amount of gas that your message's recipient handle function will use at the destination.
Behind the scenes, the DefaultIsmInterchainGasPaymaster is configured to automatically add to the provided _gasAmount all overhead gas amounts that your message will use at its destination-- this includes any gas used by the Mailbox or the default ISM (for example, verifying validator signatures). This allows messages to be fully paid for without requiring any knowledge of the internal gas usage of the destination's Mailbox contract or default ISM when a message is processed.
Find the deployed DefaultIsmInterchainGasPaymaster addresses here.
See Examples to see how this is used in practice.
When using a custom ISM (advanced)
If you are using a custom ISM, you must instead use the provided InterchainGasPaymaster. This IGP requires that the _gasAmount used when calling the payForGas or quoteGasPayment functions accounts for all gas required by the relayer to process the message on the destination chain.
The gas amount required to process the message should include:
Intrinsic transaction gas costs, including gas for calldata
The amount of gas used by the Mailbox.process function
The amount of gas used by the ISM
The amount of gas used by the message's recipient handle function
Find the deployed InterchainGasPaymaster addresses here.​
TL;DR
Application ISM
IGP Contract
_gasAmount
Default / MultisigIsm
DefaultIsmInterchainGasPaymaster
Only recipient handle function gas usage
A custom ISM
InterchainGasPaymaster
All gas used by a transaction that processes the message

Application ISM	IGP Contract	_gasAmount
Default / MultisigIsm	`DefaultIsmInterchainGasPaymaster`	Only recipient `handle` function gas usage
A custom ISM	`InterchainGasPaymaster`	All gas used by a transaction that processes the message

Paying the Correct Amount

Refunds

Last modified 1mo ago