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The 09-localhost light client module integrates with core IBC through a single sentinel localhost connection. The sentinel ConnectionEnd is stored by default in the core IBC store. This enables channel handshakes to be initiated out of the box by supplying the localhost connection identifier (connection-localhost) in the connectionHops parameter of MsgChannelOpenInit. The ConnectionEnd is created and set in store via the InitGenesis handler of the 03-connection submodule in core IBC. The ConnectionEnd and its Counterparty both reference the 09-localhost client identifier, and share the localhost connection identifier connection-localhost. 
/ CreateSentinelLocalhostConnection creates and sets the sentinel localhost connection end in the IBC store.
func (k Keeper)

CreateSentinelLocalhostConnection(ctx sdk.Context) {
    counterparty := types.NewCounterparty(exported.LocalhostClientID, exported.LocalhostConnectionID, commitmenttypes.NewMerklePrefix(k.GetCommitmentPrefix().Bytes()))
    connectionEnd := types.NewConnectionEnd(types.OPEN, exported.LocalhostClientID, counterparty, types.ExportedVersionsToProto(types.GetCompatibleVersions()), 0)

k.SetConnection(ctx, exported.LocalhostConnectionID, connectionEnd)
}
Note that connection handshakes are disallowed when using the 09-localhost client type.