# Bridge Hub questions **URL:** \ **Category:** Tech Talk\ **Tags:** xcm\ **Created:** [April 24, 2023, 12:47am UTC](https://forum.polkadot.network/t/bridge-hub-questions/2693 "2023-04-24T00:47:38Z")\ **Posts on this page:** 1\ **Showing post:** 5
**Author:** ![bkontur](https://dub1.discourse-cdn.com/flex005/user_avatar/forum.polkadot.network/bkontur/32/1112_2.png) [@bkontur](https://forum.polkadot.network/u/bkontur)\ **Post date:** [April 25, 2023, 10:34am UTC](https://forum.polkadot.network/t/bridge-hub-questions/2693/5 "2023-04-25T10:34:37Z")
> [@xlc](#): > > What are the exact steps to bridge DOT from Statemint to Statemine? We are running the whole setup on Rococo/Wococo, where we move (periodically) ROC from Rococo:Rockmine2 (statemine runtime) to Wococo:Wockmint (westmint runtime), so it is more close to the “bridge KSM from Statemine to Statemint”. Initialize bridge itself (allow tracking Rococo/Wococo finality): 1. (BridgeHubRococo) initialize bridge - Rococo governance call `xcm::Transact` with [initialize](https://github.com/paritytech/cumulus/blob/6ffe4f31c5cadfec490be7f64f3faf6b2c40cea8/bridges/modules/grandpa/src/lib.rs#L256) call 2. (BridgeHubWococo) initialize bridge - Wococo governance call `xcm::Transact` with [initialize](https://github.com/paritytech/cumulus/blob/6ffe4f31c5cadfec490be7f64f3faf6b2c40cea8/bridges/modules/grandpa/src/lib.rs#L256) call Steps to allow bridge transfer were: 1. (Rococo) `force_open_hrmp_channel(rockmine2_para_id, bridge_hub_rococo_para_id)` and back as governance call 2. (Statemine) add configuration to allow send assets to Wococo:Wockmint - Rococo governance call `xcm::Transact` with [add\_exporter\_config](https://github.com/paritytech/cumulus/blob/43ee62707d80b46a954a5742117b258b6996f3a2/parachains/pallets/bridge-transfer/src/lib.rs#L372) call 3. (Wococo) `force_open_hrmp_channel(wockmint_para_id, bridge_hub_wococo_para_id)` and back as governance call 4. (Wockmint) add configuration for trusted `UniversalOrigin/Alias` mapping - Wococo governance call `xcm::Transact` with [add\_universal\_alias](https://github.com/paritytech/cumulus/blob/43ee62707d80b46a954a5742117b258b6996f3a2/parachains/pallets/bridge-transfer/src/lib.rs#L464) call 5. (Wockmint) add configuration for trusted `reserve location` - Wococo governance call `xcm::Transact` with [add\_reserve\_location](https://github.com/paritytech/cumulus/blob/43ee62707d80b46a954a5742117b258b6996f3a2/parachains/pallets/bridge-transfer/src/lib.rs#L523) call 6. (Wockmint) create asset for `ROC` in `pallet_assets::ForeignAssets` instance - Wococo governance call `xcm::Transact` with `pallet_assets::force_create` call (looks like too much configuration, but adding new stuff does not require runtime upgrade and governance can decide about everything ) > [@xlc](#): > > What’s the XCM going to look like? > What is the reserve chain for DOT on Statemine? I am not sure what exactly “reserve chain for DOT on Statemine” means, but as it works now: - user sends some of his ROCs from Rococo:Rockmine2 to Wococo:Wockmint account with new extrinsic [transfer\_asset\_via\_bridge](https://github.com/paritytech/cumulus/blob/43ee62707d80b46a954a5742117b258b6996f3a2/parachains/pallets/bridge-transfer/src/lib.rs#L304) - first, ROCs are moved to reserve account on Rococo:Rockmine2 - it is still [open question](https://github.com/paritytech/cumulus/pull/2013#discussion_r1166707994) if reserve account will be sovereign account of local bridge hub parachain (in this case BridgeHubRococo) or sovereign account of target remote parachain (in this case Wococo:Wockmint), but probably it will be SA of target remote parachain and for that we need to finish this PR: [https://github.com/paritytech/polkadot/pull/7016](https://github.com/paritytech/polkadot/pull/7016) - second, reserved ROCs are sent with xcm over bridge as `ReserveAssetDeposited` instruction [here](https://github.com/paritytech/cumulus/blob/43ee62707d80b46a954a5742117b258b6996f3a2/parachains/pallets/bridge-transfer/src/lib.rs#L687-L693) - it is still [open for case](https://github.com/paritytech/cumulus/pull/2013#discussion_r1171077178) when we want to send back foreign assets (we should not do reserve but burn instead from reserve account) - so, here is XCM with `ReserveAssetDeposited` which will come to the local bridge hub (BridgeHubRococo) (captured from logs): ```rust Xcm([ "UnpaidExecution"{ "weight_limit":"Unlimited", "check_origin":"None" }, "ExportMessage"{ "network":"Wococo", "destination":X1(Parachain(1000)), "xcm":"Xcm("[ "WithdrawAsset(MultiAssets("[ "MultiAsset"{ "id":"Concrete(MultiLocation"{ "parents":1, "interior":"Here" }")", "fun":Fungible(50000000000) } ]"))", "BuyExecution"{ "fees":"MultiAsset"{ "id":"Concrete(MultiLocation"{ "parents":1, "interior":"Here" }")", "fun":Fungible(50000000000) }, "weight_limit":"Unlimited" }, "ReserveAssetDeposited(MultiAssets("[ "MultiAsset"{ "id":"Concrete(MultiLocation"{ "parents":2, "interior":X1(GlobalConsensus(Kusama)) }")", "fun":Fungible(100000000) } ]"))", "ClearOrigin", "DepositAsset"{ "assets":"Definite(MultiAssets("[ "MultiAsset"{ "id":"Concrete(MultiLocation"{ "parents":2, "interior":X1(GlobalConsensus(Kusama)) }")", "fun":Fungible(100000000) } ]"))", "beneficiary":"MultiLocation"{ "parents":0, "interior":X1(AccountId32{ "network":"None", "id":[212,53,147,199,21,253,211,28,97,20,26,189,4,169,159,214,130,44,133,88,133,76,205,227,154,86,132,231,165,109,162,125] }")" } } ]")" } ]) ``` - realyer relays xcm from BridgeHubRococo to BridgeHubWococo - BridgeHubWococo routes xcm over hrmp to the Wococo:Wockmint - Wococo:Wockmint’s XcmExecutor is configured (by governance) with trusted `UniversalOrigin/Alias` and `reserve location` - so it executes/dispatches xcm bellow - buy execution is paid from SA of source parachain (in this case Rococo:Rockmine2) and SA is calculated with [https://github.com/paritytech/polkadot/pull/7016](https://github.com/paritytech/polkadot/pull/7016) ```rust Xcm([ UniversalOrigin("GlobalConsensus(Rococo))", DescendOrigin(X1(Parachain(1000))), "WithdrawAsset(MultiAssets("[ "MultiAsset"{ "id":"Concrete(MultiLocation"{ "parents":1, "interior":"Here" }")", "fun":Fungible(50000000000) } ]"))", "BuyExecution"{ "fees":"MultiAsset"{ "id":"Concrete(MultiLocation"{ "parents":1, "interior":"Here" }")", "fun":Fungible(50000000000) }, "weight_limit":"Unlimited" }, "ReserveAssetDeposited(MultiAssets("[ "MultiAsset"{ "id":"Concrete(MultiLocation"{ "parents":2, "interior":X1(GlobalConsensus(Kusama)) }")", "fun":Fungible(100000000) } ]"))", "ClearOrigin", "DepositAsset"{ "assets":"Definite(MultiAssets("[ "MultiAsset"{ "id":"Concrete(MultiLocation"{ "parents":2, "interior":X1(GlobalConsensus(Kusama)) }")", "fun":Fungible(100000000) } ]"))", "beneficiary":"MultiLocation"{ "parents":0, "interior":X1(AccountId32{ "network":"None", "id":[212,53,147,199,21,253,211,28,97,20,26,189,4,169,159,214,130,44,133,88,133,76,205,227,154,86,132,231,165,109,162,125] }")" } } ]) ``` - result is that user received ROCs on Wococo:Wockmint in `pallet_assets::ForeignAssets` instance with assetId: `MultiLocation { parents: 2, X1(GlobalConsensus(Kusama)) }` _Note: Kusama is here because statemine runtime has hard-coded NetworkId as Kusama and we dont have rockmine copy of statemine with Rococo NetworkId_ @xlc hope, this answers also to your [comment](https://github.com/paritytech/cumulus/pull/2013#issuecomment-1516037941), we actually dont have any high level spec, we have several (now not up-to-date) hackmds based on which this [PR](https://github.com/paritytech/cumulus/pull/2013) is done, so we could consider this post as a latest up-to-date high level spec --- _[View the full topic](https://forum.polkadot.network/t/bridge-hub-questions/2693)._