CSE 550 Computer Network Design

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CSE 550 - Computer Network Design

• Dr. Marwan Abu-Amara
• 2nd Semester (T052)

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HSRP

• Hot Standby Routing Protocol
• Cisco proprietary
• Provides automatic router backup when configured
  on Cisco routers
• Allows one router to automatically assume
  function of second router if second router fails
• Useful when users on one subnet require
  continuous access to resources in network

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HSRP

• What happens to routing when router A, router C,
  or link A-C fails?
• OSPF, Enhanced Interior Gateway Routing Protocol
  (IGRP)
• What happens to communication between Pat
  Marceau?
• ARP, RIP, ICMP Router Discovery Protocol (IRDP),
  HSRP

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HSRP

• HSRP allows two or more HSRP-configured routers
  to use MAC address and IP network address of a
  virtual router
• Each actual router is configured with MAC address
  and IP network address of virtual router

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HSRP

• Router automatically selects one of the virtual
  MAC addresses from the range of Ciscos MAC
  address block
• Instead of configuring hosts on network 192.1.1.0
  with IP address of router A, they are configured
  with IP address of virtual router as default
  router

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How HSRP works?

• Uses priority scheme to determine which
  HSRP-configured router is to be default active
  router
• Exchange of multicast messages advertise priority
  among HSRP-configured routers
• When active router fails to send a hello message
  within configurable period of time, standby
  router with highest priority becomes active
  router

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How HSRP works?

• 3 types of multicast messages
• Hello
• conveys to other HSRP routers routers HSRP
  priority and state information (every 3 seconds
  configurable)
• Coup
• when standby router assumes function of active
  router
• Resign
• router that is active router sends this message
  when it is about to shut down or when a router
  that has higher priority sends hello message

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How HSRP works?

• HSRP-configured routers are in one of the
  following states
• Active
• router is performing packet-transfer functions
• Standby
• router is prepared to assume packet-transfer
  functions if active router fails
• Speaking and listening
• router is sending and receiving hello messages
• Listening
• router is receiving hello messages

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Multigroup HSRP (MHSRP)

• Extension of HSRP that allows a single router
  interface to belong to more than one Hot Standby
  group

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Load Sharing

• Half of workstations on LAN are configured for
  router A, and other half are configured for
  router B