This article presents our work proposing in-network caching in IP-based networks by adding a content identifier into a newly defined IPv6 extension header, where the new architecture is named CAIP. CAIP abandons the complicated name-based forwarding table in ICN, and instead integrates IP routing lookup with cache index lookup, which is compatible with the IP network and also inherits the proven advantages of ICN. Cache index exchanging and cooperative caching are implemented between one-hop CAIP enabled neighboring routers, which is simple but efficient. Moreover, for per-chunk caching, as an extension, bitmap is introduced to merge multiple request packets into one. Performance analysis shows that CAIP gains significant performance improvement in terms of access delay and traffic load.