DITECH Packet Voice Processor, Руководство по управлению

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Media Provisioning
Packet Voice Processor Commands Manual
6.4.3 PVP Network Configuration with HSRP/VRRP Fail-Over
A Packet Voice Processor system installation can be setup to provide for router fail-
over using the Hot Standby Routing Protocol (HSRP) or Virtual Router Redundancy
Protocol (VRRP). HSRP is defined in RFC 2281. VRRP is defined in RFC 2338.
Note For a complete list of Packet Voice Processor supported protocols, see Appendix A
on page 387 .
6.4.3.1 HSRP
As defined in RFC 2281, HSRP provides a mechanism designed to support non-
disruptive failover of IP traffic in certain specific circumstances. In particular, this
protocol protects against the failure of the first hop router when the source host
cannot learn the IP address of the first hop router dynamically. The protocol is
designed for use over multi-access, multicast or broadcast capable LANs (for
example, Ethernet).
Using HSRP, a set of routers work in concert to present the illusion of a single virtual
router to the hosts on the LAN. This set is known as an HSRP group or a standby
group. A single router elected from the group is responsible for forwarding the
packets that hosts send to the virtual router. This router is known as the active router.
Another router is elected as the standby router. In the event that the active router
fails, the standby router assumes the packet forwarding duties of the active router.
Although an arbitrary number of routers may run HSRP, only the active router
forwards the packets sent to the virtual router.
To minimize network traffic, only the active and the standby routers send periodic
HSRP messages once the protocol has completed the election process. If the active
router fails, the standby router takes over as the active router. If the standby router
fails or becomes the active router, another router is elected as the standby router.
On a particular LAN, multiple hot standby groups may coexist and overlap. Each
standby group emulates a single virtual router. For each standby group, a single well-
known MAC address is allocated to the group, as well as an IP address. The IP
address should belong to the primary subnet in use on the LAN, but must differ from
the addresses allocated as interface addresses on all routers and hosts on the LAN,
including virtual IP addresses assigned to other HSRP groups.
If multiple groups are used on a single LAN, load splitting can be achieved by
distributing hosts among different standby groups.
Figure 6-4 on page 71 displays a Packet Voice Processor network configuration
using HSRP with an active and standby router to provide for router failover.
6.4.3.2 VRRP
As defined in RFC 2338, VRRP is designed to eliminate the single point of failure
inherent in the static default routed environment. VRRP specifies an election protocol
that dynamically assigns responsibility for a virtual router to one of the VRRP routers
on a LAN. The VRRP router controlling the IP address(es) associated with a virtual
router is called the Master, and forwards packets sent to these IP addresses. The
election process provides dynamic fail-over in the forwarding responsibility should
the Master become unavailable. Any of the virtual router's IP addresses on a LAN
can then be used as the default first hop router by end-hosts. The advantage gained
from using VRRP is a higher availability default path without requiring configuration
of dynamic routing or router discovery protocols on every end-host.