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Nash!Com rDNS Replacement
This problem is specific to Lotus Domino Servers running on Windows platforms. However this solution might also help to increase performance on other operating systems like Linux. The solution is based on a Servertask that copies documents from standard domlog.nsf into a new Domino log database while checking the name for the requesting IP address. This is done asynchronous and has no impact on server performance because is independent from the HTTP stack. It uses an internal cache that not just caches the names but also the status for the request. In case an IP address has no name it will not requesting it again for the following requests. This does significantly reduce the time for resolving addresses if the IP has no DNS entry specified. Some technical background This section contains very technical information we found out about the webserver response time problem some customers had accessing a Domino based website. We identified this problem as not being a Domino problem. The problem is caused by and combination of the winsock-request performed by Domino, that only occurs on NT platforms in combination with 'some' client environments if DNS Lookup is enabled in the server document. It is not caused by Domino, but Domino is using a feature of NT that isn't working the way it should work. Lotus Domino uses the winsock function gethostbyaddr() to resolve the requesting IP address to get the host name. The gethostbyaddr() call uses the following sequence:
Steps one and two are just local actions and are handled very fast. Step three uses a DNS query to resolve the address via IN-ARPA PTR (address-to-name) records. This should be fast, because it queries the local ISPs DNS server in most configurations. If the DNS server is not authoritative for the domain and does not hold the entry in cache it makes a query to another DNS server. But after the local DNS server found out about the address it holds it in it's cache (until time to live is reached). Therefore subsequent queries result in a non authoritative but faster answer from the local DNS server. Step four uses a NetBIOS Adapter Status Request (RFC 1001/1002) directly to the requesting client. This might be a performance problem, if the query has no success. Using a small winsock test program we found out that the timeout interval is approximately 5 seconds. Lotus Domino uses gethostbyaddr() for each GET request. In most cases you have a lot of GET requests for frameset, frames and pictures. If each of the request forces a NetBIOS Adapter Status Request that times out. If the address isn't found or timed out, it can't be cached. If a DNS name is specified, the DNS query gets a fast response. But if no DNS entry is defined and the NetBIOS Adapter Status Request times out we get the slow answer time the customer found out using their proxy or any other client using an IP address without DNS. It depends on the configuration of the firewall on the other side if the NetBIOS Adapter Status Request times out. The port used for this kind of lookups is port 137 and is called Netbios Name Service. The NetBIOS Adapter Status Request Feature was introduced in NT Version 3.51 and I could not find any way to disable this feature. MSDN Article ID: Q138086 describes this feature.
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