Download: Linux Virtual Server Tutorial

Linux Virtual Server Tutorial Horms (Simon Horman) VALinuxSystems Japan, K.K. with assistance from NTTComware July … … 2003. Revised March 2004 http://www.ultra Abstract The LinuxVirtual Server Project (LVS) allows load balancing of networked services such as web and mail servers using Layer 4 Switching. It is extremely fast and allows such services to be scaled to service 10sor 100softhousands of simultaneous connections. The purpose of this …

1 LVS Basics This section will cover the basics of how LVS works. How to obtain and install LVS, and how to configure for its main modes of operation. In short it will cover how to setup LVS to load balance TCPandUDP services. Terminology Linux Director: Host with Linuxand LVS installed which receives packets from end users and forwards them to real servers. End User: Host that originatesa connection. Real Server: Host that terminatesa connection. This will be running some sort of daemon such as Apache. A single host maybe actin more than one of the above roles at the same time. Virtual IPAddress (VIP): The IP address assigned to a service that a Linux Director will handle. Real IPAddress (RIP): The IP address ofa Real Server. Layer 4Switching… Forwarding Packets The LinuxVirtual Server has three different ways of forwarding packets; network address translation (NAT), IP-IP encapsulation (tunnelling) and direct routing. •Network Address Translation (NAT): A method of manipulating the source and/ordesti- nation port and/or address of a packet. The most common use of this is IP masquerading which is often used to enable RFC 1918[2]private networks to access the Internet. In the context of layer 4 switching, packets are received from end users and the destination port and IPaddress are changed to that of the chosen real server. Return packets pass through the linux director at which time the mapping is undone so the end user sees replies from the expected source. •Direct Routing: Packets from end users are forwarded directly to the real server. The IP packet is not modified, so the real servers must be configured to accept traffic for the virtual server’sIP address. This can be done using a dummy interface or packet filtering to redirect traffic addressed to the virtual server’sIP address toalocalport. The real server may send replies directly back to the end user. Thus, the linuxdirector does not need to be in the return path. •IP-IP Encapsulation (Tunnelling): Allows packets addressed to an IP address to be redirected to another address, possibly on a different network. In the context of layer 4 switching the behaviour is very similar to that of direct routing, except that when packets are forwarded they are encapsulated in an IP packet, rather than just manipulating the ethernetframe. The main advantage of using tunnelling is that real servers can be on a different networks.

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