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USENIX Technical Program - Abstract - 13th Systems Administration Conference - LISA '99

NetMapper: Hostname Resolution Based on Client Network Location

Josh Goldenhar, Cisco Systems, Inc.


Large buildings, sprawling campuses and multiple remote sites have led to an explosion in the number of IP networks for corporate computing. Workgroups are spread over multiple networks. Servers are configured with multiple network interfaces in an attempt to optimize access. When geographic or capacity issues arise, separate servers which replicate desired functionality are placed in network proximity to their clients. Some of these servers provide tool trees which have operating system (OS) and architecture specific binaries. The optimal server or server interface for a given client may or may not have a presence on the client's network. In such an environment, how can an administrator guarantee a network client is utilizing the desired network interface or server?

NetMapper provides a framework for resolving hostnames (real or virtual) based on the client host's location within a network hierarchy. For servers with multiple network interfaces, NetMapper chooses the best interface. For multiple servers providing replicated services via a virtual hostname, NetMapper chooses the best server. For file servers providing OS and architecture specific filesystems, NetMapper chooses the best server taking into account client OS, architecture and network attributes. In all cases, 'best' is defined by the NetMapper administrator. As a side benefit, NetMapper allows systems and network administrators to view their network hierarchy at-a-glance.

The core of NetMapper functionality is a Perl module ( and a configuration daemon (nmconfd) which serves the configuration information to NetMapper clients. NetMapper has been implemented in the Cisco engineering environment by developing a small program called localmapper which runs on all UNIX clients and generates entries in the client's local /etc/hosts file. localmapper optionally generates a small NFS automounter map for OS and architecture specific remote partitions. This fairly small collection of tools allows systems administrators to choose which servers UNIX network clients use based on geography, workgroup or any arbitrary rationale that can be defined via groups of networks.

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