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Distributed Systems: Naming (Continued): 

Distributed Systems: Naming (Continued) CS 654 Lecture 11 October 23, 2006

Example: DNS: 

Example: DNS Name space is a tree of nodes. Label can be 63 characters. Max name is 255 characters. Subtree is a domain. Pathname is a domain name. A zone is the part of the tree that a nameserver is responsible for. A domain is made up of one or more zones.

DNS Node: 

DNS Node The most important types of resource records forming the contents of nodes in the DNS name space.

DNS Subdomains: 

DNS Subdomains Part of the description for the vu.nl domain which contains the cs.vu.nl domain.

Example: X.500: 

Example: X.500 DNS resolves a name to a node in the namespace graph. X.500 is a directory service, which allows more general queries. Consists of a set of records. Each record is a list of attribute-value pairs, with possible multiple values.

X.500 Directory Entry: 

X.500 Directory Entry A simple example of a X.500 directory entry using X.500 naming conventions. /C=NL/O=Vrije Universiteit/OU=Math. & Comp. Sc.

Slide8: 

Collection of all entries is a Directory Information Base (DIB). Each naming attribute is a Relative Distinguished Name (RDN). The RDNs, in sequence, can be used to form a Directory Information Tree (DIT).

The X.500 Name Space (2): 

The X.500 Name Space (2) Part of the directory information tree.

Children Nodes: 

Children Nodes Two directory entries having Host_Name as RDN.

Mobile Entities: 

Mobile Entities

Naming vs. Locating: 

Naming vs. Locating DNS works well because we assume that local layer changes often, but that it is also efficient. Suppose we want to change a.cs.binghamton.edu to foo.cs.soton.ac.uk. How? Change the IP address for a. Make a “symbolic link” from a to b. Compare and contrast?

Naming versus Locating Entities: 

Naming versus Locating Entities Direct, single level mapping between names and addresses. Two-level mapping using identities and separate location service.

Broadcast/multicast Location: 

Broadcast/multicast Location How does Ethernet addressing work? MAC address How does your switch/hub know the IP to MAC address mapping? ARP, sends request, gets answer Disadvantage? Multicast uses? Location (cannot be used for transmission) Question, how does the post office deal with mobility?

Forwarding: 

Forwarding When entity moves, leave a reference. Disadvantages? Chain too long if lots of movement. Vulnerable to failure Performance is bad

Forwarding Pointers in SSP: 

The principle of forwarding pointers using (proxy, skeleton) pairs. Forwarding Pointers in SSP

Shortcut: 

Shortcut Redirecting a forwarding pointer, by storing a shortcut in a proxy.

Home-Base Approaches: 

Home-Base Approaches Mobile IP All hosts use fixed IP as ID (home location). Initially directed to home agent Tunnels first packet, then responds

Home-Based Approaches: 

Home-Based Approaches The principle of Mobile IP.

Hierarchical Approaches: 

Hierarchical Approaches First try local registry, then try the home. Can generalize to multiple tiers.

Hierarchical Approaches: 

Hierarchical Approaches Hierarchical organization of a location service into domains, each having an associated directory node.

Slide22: 

R E: N1 N1 E: Addr N2 E: N2 E C

Hierarchical Approaches: 

Hierarchical Approaches Looking up a location in a hierarchically organized location service.

Hierarchical Approaches: 

Hierarchical Approaches An example of storing information of an entity having two addresses in different leaf domains.

Hierarchical Approaches: 

Hierarchical Approaches An insert request is forwarded to the first node that knows about entity E.

Hierarchical Approaches: 

Hierarchical Approaches A chain of forwarding pointers to the leaf node is created.