In simple terms
Inter-Blockchain Communication, usually shortened to IBC, is a set of rules that lets separate blockchains send tokens and messages to each other directly. It is like two banks that each keep an up-to-date copy of the other's signature book, so they can confirm every transfer themselves without a middleman.
Definition
A protocol that lets independent blockchains exchange tokens and data by verifying each other's state with on-chain light clients.
In depth
IBC was developed in the Cosmos ecosystem and is used by many chains built with the Cosmos SDK, although its design is not limited to them. Each connected chain runs a light client of the other that tracks its block headers and validator set, so it can check cryptographic proofs that a packet was committed on the counterpart. Off-chain relayers carry packets and proofs between chains, and they cannot forge them, because each chain verifies the proofs itself. Communication runs over connections and channels, with application standards on top, such as ICS-20 for fungible token transfers. A token moved over IBC carries a denomination trace recording its path, so the same asset arriving by different routes appears as different tokens.
What does Inter-Blockchain Communication (IBC) mean?
Two chains first establish a connection by creating a light client of each other and completing a handshake, then open a channel for a specific application such as token transfers. When a user sends tokens, the source chain escrows or burns them and records a packet commitment. A relayer picks up the packet and submits it to the destination chain with a proof. The destination chain checks the proof against its light client and mints a voucher token for the user. An acknowledgment travels back, and if the packet times out instead, the source chain refunds the tokens.
An example
Someone holds 100 ATOM on the Cosmos Hub and wants to trade on a decentralized exchange running on another Cosmos chain. They send the tokens over IBC, paying a fee of about $0.01, and within a minute they see 100 ATOM on the destination chain, recorded under a long IBC denomination. Sending the tokens back over the same channel returns them as ordinary ATOM.
Figures are illustrative only.
What beginners get wrong
- Many people assume IBC tokens with the same name are interchangeable. A token that arrived through a different route or channel has a different denomination, and apps may treat it as a separate asset.
- Some users believe relayers hold or control the funds in transit. Relayers only carry messages and proofs, and the chains verify those proofs themselves.
- It is easy to think IBC makes every connected chain equally safe. A light client verifies what the other chain's validators agreed on, so a chain with a weak or compromised validator set can still send bad data.
- Some users expect IBC to reach any blockchain. It works only between chains that implement it and have set up connections, although extensions such as IBC Eureka reach beyond the Cosmos ecosystem.
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