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Intro

1. What is an outpost chain

  • Chain that owns a different native bridge not controlled by the PP (Pessimistic Proof)
  • Is EVM compatible (in a first stage)
  • The chain already exists, we are not involved on the genesis
  • The state transition is not controlled by us (not controlled sequencer)
  • Has its own finality
  • All outposts will have a customGasToken that will be the native token of the chain
    • Outpost chains can not have native ether token
  • Examples:
    • Base
    • Optimism
    • BSC

2. Architecture

Outpost Architecture
Outpost Architecture

Key points:

  • The outpost chain has its own native bridge and sequencer — neither is controlled by the Agglayer
  • Agglayer L2 contracts (AgglayerBridgeL2, AgglayerGERL2) are deployed on the outpost chain
  • The Pessimistic Proof verifies the bridge activity on the outpost
  • The outpost needs the Agglayer Core SC to be deployed on the L1 chain

3. Particularities

  • Bridge, GER and wTokens have different addresses
  • Reorgs can happen not controlled by the agglayer
    • New functions in the bridge to manage Local Exit Tree possible mismatches

4. Flow examples

4.1 Outpost with native ETH

Example flow of an outpost having gasTokenNetwork different than native networkID/rollupID:

  • Initialize params:
    • GasTokenNetwork: 0 (ethereum)
    • GasTokenAddress: 0x000....000 (ethereum)
sequenceDiagram
    participant User
    participant L1_Base_Bridge
    participant Native_Bridge_Base
    participant Agglayer_Bridge_Base
    participant L1_Agglayer_Bridge

    Note left of User: User has ETH
    User ->> L1_Base_Bridge: bridge to base
    L1_Base_Bridge ->> L1_Base_Bridge: lock ETH
    L1_Base_Bridge ->> Native_Bridge_Base: bridge
    Native_Bridge_Base ->> User: mint baseETH
    Note left of User: User has baseETH
    User ->> Agglayer_Bridge_Base: bridge to L1 (from aggLayer)
    Agglayer_Bridge_Base ->> Agglayer_Bridge_Base: lock baseETH
    Agglayer_Bridge_Base ->> L1_Agglayer_Bridge: bridge
    L1_Agglayer_Bridge ->> User: ❌❌ There is no ETH on bridge to send ❌❌

4.2 Outpost with native token

Example flow of an outpost having gasTokenNetwork same than native networkID/rollupID: Initialize params: - GasTokenNetwork: 2 (base rollupId) - GasTokenAddress: 0x002....002 (custom address) 

sequenceDiagram
    participant User
    participant L1_Base_Bridge
    participant Native_Bridge_Base
    participant Agglayer_Bridge_Base
    participant L1_Agglayer_Bridge

    Note left of User: User has ETH
    User ->> L1_Base_Bridge: bridge to base
    L1_Base_Bridge ->> L1_Base_Bridge: lock ETH
    L1_Base_Bridge ->> Native_Bridge_Base: bridge
    Native_Bridge_Base ->> User: mint baseETH
    Note left of User: User has baseETH
    User ->> Agglayer_Bridge_Base: bridge to L1 (from aggLayer)
    Agglayer_Bridge_Base ->> Agglayer_Bridge_Base: lock baseETH
    Agglayer_Bridge_Base ->> L1_Agglayer_Bridge: bridge
    L1_Agglayer_Bridge ->> User: mint wrappedBaseETH
    Note left of User: User has wrappedBaseETH ✅