wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

19-14 Industrial Communication Systems
LAN
Master
Router rA VRID 1
Priority: 250
Ethernet IP address:
192.168.44.2
rA
VRID 1
Virtual IP 192.168.44.1
rB
Backup
Router rB VRID 1
Priority: 20
Ethernet IP address:
192.168.44.3
FIGURE 19.8
Simple VRRP example.
When the problem with router rA is resolved, and depending on its configuration, either of two
situations would occur:
• If Router rA is configured to start as master, it will force an election immediately by sending its
first advertisement as master. Router rB will receive this advertisement and transition to backup
state.
• If Router rA is configured to start as backup, it will transition from initialization to backup state.
Nothing will happen until it receives an advertisement from router rB. Router rB has a lower
priority than router rA, so router rA will start an election by commencing its transition to master
state and sending an advertisement. When it receives this advertisement, router rB will transition
to backup state because router rA has higher priority.
Although VRRP is based on Cisco’s proprietary Hot Standby Router Protocol (HSRP, [26]) concepts,
VRRP is actually a standardized version of Cisco’s HSRP. Those protocols, while similar in concept, are
not compatible. There are a great number of implementations besides the Cisco devices one.
References
1. R. Zurawski, ed., The Industrial Communication Technology Handbook, CRC Press, Boca Raton,
FL, 2005.
2. W. Stallings, High Speed Networks and Internets. Performance and Quality of Service, Prentice Hall,
Englewood Cliffs, NJ, 2002.
3. J. García Tomás, J.L. Raya, and V. Rodrigo, Alta velocidad y calidad de servicio en Redes IP, Ed.
Ra-Ma, Alfaomega, Mexico, 2002.
© 2011 by Taylor and Francis Group, LLC