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Content Lookup

   figure155
Figure 3: Internet Name Resolution Protocol

Name lookup is supported by the Internet Name Resolution Protocol (INRP); this protocol is reverse-compatible with DNS, using the same record types and packet format, but with different underlying semantics. Clients initiate a content request by contacting a local content router, just as they would contact a preconfigured DNS server. Their requests may include just the ``server'' portion of a URL, although in the long run it would be advantageous to include the entire URL.

Each content router maintains a set of name-to-next-hop mappings, just as an IP router maps address prefixes to next hops. (This name routing information is maintained using a dynamic routing protocol detailed below.) When an INRP request arrives, the desired name is looked up in the name routing table, and the next hop is chosen based on information associated with the known routes. The content router forwards the request to the next content router, and in this way the request proceeds toward the ``best'' content server, as shown in Figure 3. The routing information kept for a name is typically just the path of content routers to the content server, although it may be augmented with load information or metrics directly measured by a content router.

When an INRP request reaches the content router adjacent to the ``best'' content server, that router sends back a response message containing the address of the preferred server. This response is sent back along the same path of content routers. If no response appears, intermediate content routers can select alternate routes and retry the name lookup. A client application which is INRP-aware can also request exclusion of a non-responsive server in an INRP request.

In this fashion, client requests are routed over the best path to the desired content in the normal case, yet can recover from a failing server or out-of-date routing information. INRP thus provides an ``anycast'' capability at the content level, with network and client control to re-select alternatives based on direct experience with the chosen server.

Routing is done at the granularity of server names rather than full URLs (although the latter could be useful for proxies or content transformers). This decision does limit some possible caching applications, but provides little practical obstacle to web designers, since directory names from the file portion of a URL can be moved into the front of the server name (i.e., http://foo.com/bar/index.html can become http://bar.foo.com/index.html). Routing is longest-suffix match, since this can be much more efficiently performed than other possible matches on URLs.

Relaying the name lookup request across the same path as the packets are to flow ensures that naming is as available as endpoint connectivity-- and that the replica selected is actually reachable. Moreover, the trust in name lookup matches the trust in delivery because both depend on the same set of network nodes. Also, the name lookup load for a path is imposed just on the routers on that path, so upgrading a router on that path for increased data capacity can also upgrade the name lookup capacity on that path. Additionally, we are exploring piggybacking connection setup these name lookups, in which case the name lookup would progress all the way to the content server itself.


next up previous
Next: Name-Based Routing Up: Network-Integrated Content Routing Previous: Network-Integrated Content Routing

Mark Geoffrey Gritter
Fri Jan 19 09:19:43 PST 2001