Nortel Networks WEB OS 212777 - Manual (Page 312)

Web OS 10.0 Application Guide
312 n Chapter 12: Global Server Load Balancing
212777-A, February 2002
Using Border Gateway Protocol for GSLB
Border Gateway Protocol (BGP)-based GSLB utilizes the Internet’s routing protocols to local-
ize content delivery to the most efficient and consistent site. It does so by using a shared IP
block that co-exists in each Internet Service Provider’s (ISP’s) network and is then advertised,
using BGP, throughout the Internet.
Because of the way IP routing works, BGP-based GSLB allows for the routing protocols to
route DNS requests to the closest location, which then returns IP addresses of that particular
site, locking in the requests to that site. In effect, the Internet is making the decision of the best
location for you, avoiding the need for advanced GSLB.
Some corporations use more than one ISP as a way to increase the reliability and bandwidth of
their Internet connection. Enterprises with more than one ISP are referred to as being multi-
homed. Instead of multi-homing a network to several other networks, BGP-based GSLB
enables you to multi-home a particular piece of content (DNS information) to the Internet by
distributing the IP blocks that contain that content to several sites.
When using DNS to select the site, a single packet is used to make the decision so that the
request will not be split to different locations. Through the response to the DNS packet, a client
is locked in to a particular site, resulting in efficient, consistent service that cannot be achieved
when the content itself is shared.
For example, in multi-homing, you can connect a data center to three different Internet provid-
ers and have one DNS server that has the IP address 1.1.1.1. In this case, all requests can be
received via any given feed but are funneled to the same server on the local network. In BGP-
based GSLB, the DNS server (with the IP address 1.1.1.1) is duplicated and placed local to the
peering point instead of having a local network direct traffic to one server.
When a particular DNS server receives a request for a record (in this case, the Web switch), it
returns with the IP address of a virtual server at the same site. This can be achieved using the
local option ( /cfg/slb/gslb/local ena ) in the GSLB configuration. If one site is
saturated, then the switch will failover and deliver the IP address of a more available site.
For more information on configuring your switch to support BGP routing, see “Border Gate-
way Protocol (BGP)” on page 36 .