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Advanced Configuration and Management Guide
Overview of Standby Router Protocol (SRP)
SRP allows alternate paths to be provided to a host. To provide path redundancy between given hosts, a virtual
router with its own unique IP addresses is created. The virtual router is created by assigning these unique IP
addresses to ports on existing routing switches in the network—routing switches that could provide a path
between the given hosts.
NOTE: Virtual IP router addresses are in addition to the IP address assigned to each IP interface.
For example, in Figure 13.1, suppose you want to provide continual connectivity between Host 1 and Host 3 with
the use of redundant paths. A virtual router is created by assigning the same virtual router IP address to all
physical interfaces that will provide redundant paths for that portion of the network. Virtual router IP address
192.53.5.1 is assigned to interfaces A and B, and the virtual router IP address 192.55.4.1 is assigned to interfaces
C and D. Notice that in both cases, these virtual addresses are in addition to their physical IP addresses.
The virtual IP address also serves as the default router for the hosts. Hosts 1 and 2 reference the virtual IP router
address 192.53.5.1 as their default router and Host 3 references the virtual router IP address, 192.55.4.1.
If Router 1 goes down, then Router 2 provides connectivity between Host 1 and Host 3.
Host 1 Host 2
Virtual
Router
Router 1
Router 2
Default Router
192.53.5.1
192.53.5.1 192.53.5.1 192.53.5.1
Default Router
192.53.5.1
192.53.5.2
192.53.5.3
(A)
(B)
Default Router
192.55.4.1
192.55.4.1 192.55.4.1192.55.4.1
Preference = 200
Active
Preference = 60
Standby
192.55.4.2 192.55.4.3
(C)
(D)
Host 3
Router 1:
Router 2:
IP Address for Interface A: 192.53.5.2
Virtual Router IP address for Interface A: 192.53.5.1
IP Address for Interface B: 192.53.5.3
Virtual Router IP address for Interface B: 192.53.5.1
IP Address for Interface C: 192.55.4.2
Virtual Router IP address for Interface C: 192.55.4.1
IP Address for Interface D: 192.55.4.3
Virtual Router IP address for Interface D: 192.55.4.1
Figure 13.1 SRP operating in an HP 9304M network
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