Cisco WS-X6416-GE-MT - Interface Module - Expansion Manual de usuario descargar pdf (Pagina 46)

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is maintained during a supervisor failover. This helps to reduce the failover time. However, the port

states are not maintained, so connections to other devices will flap.

The failover time for the system to start forwarding traffic in RPR+ is approximately 30 seconds.

The actual failover time is dependent on the size and complexity of the configuration.

Nonstop Forwarding with Stateful Switchover (NSF/SSO)

Both Cisco IOS Software and the Cisco Catalyst OS support NSF with SSO. The primary

differentiators apply in where and how these features are applied, with the more advanced forms of

these features being deployed first in Cisco IOS Software. SSO expands the RPR+ capabilities to

provide transparent failover of Layer 2 protocols when a supervisor failure occurs. SSO is stateful

for Layer 2 protocols. PFC and Distributed Forwarding Card (DFC) hardware tables are maintained

across a switchover. This allows for transparent failover at Layer 2 and Layer 4. NSF works in

conjunction with SSO to help ensure Layer 3 integrity following a switchover. It allows a router

experiencing the failure of an active supervisor to continue forwarding data packets along known

routes while the routing protocol information is recovered and validated. This forwarding can

continue to take place by using graceful restart mechanisms that allow peering arrangements to

recover upon failover, thus avoiding unnecessary route flaps and network instability.

The failover time is 0 to 3 seconds with NSF/SSO. More information on NSF/SSO can be found at

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/prod_white_paper0900aecd80

1c5cd7.shtml.

Hot Standby Router Protocol (HSRP)

The Hot Standby Router Protocol (HSRP) provides network redundancy for IP networks, helping

ensure that user traffic immediately and transparently recovers from first hop failures in network

edge devices or access circuits. HSRP provides a Layer 2 and Layer 3 virtual address that is

shared between two or more Cisco routing devices to help ensure network resiliency. It uses an

election algorithm combined with statically assigned virtual IP address and Layer 2 MAC address

for transparent fault recovery. For more information, visit

http://www.cisco.com/en/US/partner/tech/tk648/tk362/tk321/tsd_technology_support_sub-

protocol_home.html.

Virtual Router Redundancy Protocol (VRRP)

The Virtual Router Redundancy Protocol (VRRP) provides a function very similar to the Cisco

proprietary Hot Standby Router Protocol (HSRP). VRRP is designed to eliminate the single point of

failure inherent in a 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 failover

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.

Gateway Load Balancing Protocol (GLBP)

The Gateway Load Balancing Protocol (GLBP) provides load-balancing over multiple gateways

through a single virtual IP address and multiple virtual MAC addresses. This protocol is similar to

Host Standby Router Protocol (HSRP) and Virtual Router Redundancy Protocol (VRRP). GLBP

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