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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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24.6.2 VRRP definitions<br />

24.6.3 VRRP overview<br />

Some terms used in VRRP are:<br />

VRRP router A router running the Virtual Router Redundancy<br />

Protocol. It can participate in one or more virtual<br />

routers.<br />

Virtual router An abstract object managed by VRRP that acts as a<br />

default router for hosts on a shared LAN. It consists of<br />

a virtual router identifier <strong>and</strong> a set of associated <strong>IP</strong><br />

addresses depending on the definition, across a<br />

common LAN. A VRRP router can back up one or<br />

more virtual routers.<br />

<strong>IP</strong> address owner The VRRP router that has the virtual router's <strong>IP</strong><br />

addresses as real interface addresses. This is the<br />

router that, when up, responds to packets addressed<br />

to one of these <strong>IP</strong> addresses for ICMP pings, <strong>TCP</strong><br />

connections, <strong>and</strong> so on.<br />

Primary <strong>IP</strong> address An <strong>IP</strong> address selected from the set of real interface<br />

addresses. One possible selection algorithm is to<br />

always select the first address. VRRP advertisements<br />

are always sent using the primary <strong>IP</strong> address as the<br />

source of the <strong>IP</strong> packet.<br />

Virtual router master The VRRP router that is assuming the responsibility of<br />

forwarding packets sent to the <strong>IP</strong> addresses<br />

associated with the virtual router <strong>and</strong> answering ARP<br />

requests for these <strong>IP</strong> addresses. Note that if the <strong>IP</strong><br />

address owner is available, it will always become the<br />

master.<br />

Virtual router backup The set of VRRP routers available to assume<br />

forwarding responsibility for a virtual router if the<br />

current master fails.<br />

VRRP specifies an election protocol to provide the virtual router function<br />

described earlier. All protocol messaging is performed using <strong>IP</strong> multicast<br />

datagrams (see Chapter 6, “<strong>IP</strong> multicast” on page 237), thus the protocol can<br />

operate over a variety of multiaccess LAN technologies supporting an <strong>IP</strong><br />

multicast. Each VRRP virtual router has a single well-known MAC address<br />

allocated to it. The virtual router MAC address is used as the source in all<br />

periodic VRRP messages sent by the master router to enable bridge learning in<br />

an extended LAN.<br />

916 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong>

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