# IBC Relayer

Running an IBC relayer for Nomic works mostly the same as with other Cosmos chains, but with a few caveats:

1. Currently, Nomic is only compatible with [Hermes](https://hermes.informal.systems) and does not support the ibc-go relayer.
2. Hermes must be configured with a custom proof spec. Please see the example configuration below.

## 1. Configure Hermes

Here's an example Hermes configuration relaying between a local Nomic and Osmosis node:

<pre class="language-toml"><code class="lang-toml"><strong># ~/.hermes/config.toml
</strong>
[[chains]]
id = 'nomic-stakenet-3'
rpc_addr = 'http://127.0.0.1:26657'
event_source = { mode = 'pull' }
grpc_addr = 'http://127.0.0.1:9001'
rpc_timeout = '10s'
account_prefix = 'nomic'
key_name = 'testkey'
store_prefix = 'ibc'
max_gas = 40000000
gas_price = { price = 0.001, denom = 'stake' }
clock_drift = '20s'
proof_specs = '''
[
  {
    "inner_spec": {
      "child_order": [
        0,
        1,
        2
      ],
      "child_size": 32,
      "empty_child": "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
      "min_prefix_length": 1,
      "max_prefix_length": 1,
      "hash": 6
    },
    "leaf_spec": {
      "hash": 6,
      "prehash_key": 0,
      "prehash_value": 0,
      "length": 4,
      "prefix": "AA"
    },
    "max_depth": 0,
    "min_depth": 0
  },
  {
    "inner_spec": {
      "child_order": [
        0
      ],
      "child_size": 32,
      "empty_child": "",
      "min_prefix_length": 0,
      "max_prefix_length": 0,
      "hash": 6
    },
    "leaf_spec": {
      "hash": 6,
      "prehash_key": 0,
      "prehash_value": 0,
      "length": 0,
      "prefix": ""
    },
    "max_depth": 0,
    "min_depth": 0
  }
]
'''

[[chains]]
id = 'osmosis-1'
rpc_addr = 'http://127.0.0.1:26757'
grpc_addr = 'http://127.0.0.1:9090'
websocket_addr = 'ws://127.0.0.1:26757/websocket'
rpc_timeout = '10s'
account_prefix = 'osmo'
key_name = 'osmosis'
address_type = { derivation = 'cosmos' }
store_prefix = 'ibc'
default_gas = 5000000
max_gas = 15000000
gas_price = { price = 0.0026, denom = 'uosmo' }
gas_multiplier = 1.1
max_msg_num = 20
max_tx_size = 209715
clock_drift = '20s'
max_block_time = '10s'
trusting_period = '10days'
trust_threshold = { numerator = '1', denominator = '3' }
[chains.packet_filter]
policy = 'allow'
list = [
  ['transfer', 'channel-5555'], # nomic-stakenet-3
]
</code></pre>

The `proof_specs` and `event_source` fields for Nomic are the main differences to note for those otherwise familiar with IBC relaying with Hermes.

Please refer to the [Hermes docs](https://hermes.informal.systems) for more information.

## 2. Run gRPC server

Nomic features a gRPC server to support IBC relaying, which implements only the minimum set of gRPC methods required by Hermes. The server does not run by default, and must be run in a separate process with:

```bash
# default port 9001
nomic grpc
```

or:

```bash
nomic grpc <PORT>
```

## 3. Fund relayer with nBTC

Fees for IBC transactions are paid with nBTC (1 sat per tx). After you've configured your relayer, you'll need to fund its Nomic account (`hermes keys list --chain nomic-stakenet-3` to see the address) with nBTC.

## 4. (Optional) Relay operator keys

To ensure that nBTC is recoverable by the remote chain's validator set in the event of an Emergency Disbursal, run:

```bash
nomic relay-op-keys <COUNTERPARTY-RPC> <CLIENT_ID>
```

This command may be re-run anytime to refresh the operator keys of the remote chain's validator set. If an Emergency Disbursal occurs on Nomic, a portion of the Bitcoin reserves equal to the nBTC held in channels backed by the specified client will become spendable by 2/3+ of the voting power of that network's top 30 validators.

## Other notes

Below are a couple other notes to keep in mind, given Nomic's custom IBC implementation.

### Channel ports

For channels supporting token transfers, the Nomic channel port **must** be `transfer`. ICS 20 is the only application-layer standard currently supported by Nomic:

```bash
hermes create channel --a-chain osmosis-1  --b-chain nomic-stakenet-3 --a-port transfer --b-port transfer --new-client-connection
```

### Manual clearing

Typically, the main Hermes process (`hermes start`) will properly relay packets between Nomic and its counterparty. However, if it seems like an event has been missed by Hermes, packets can be manually cleared (bidirectionally) with:

```bash
hermes clear packets --chain nomic-stakenet-3 --port transfer --channel channel-1
```


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