Information Technology Reference
In-Depth Information
4.
If Router A goes offline, Router B takes over as the active router, continuing the deliv-
ery of the workstation's packets. The change is transparent to the workstation.
VRRP
VRRP is a router redundancy protocol defined in RFC 3768. RFC 5768 defined VRRPv3
for both IP v4 and IP v6 net work s. VRRP is bas ed on Cis co's HSRP, but is not compat ible.
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 ad-
dresses 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 re-
sponsibility should the master become unavailable. This allows any of the virtual router IP
addresses on the LAN to be used as the default first hop router by end hosts. The virtual
router backup assumes the forwarding responsibility for the virtual router should the mas-
ter fail.
GLBP
GLBP protects data traffic from a failed router or circuit, such as HSRP, while allowing
packet load sharing between a group of redundant routers. The difference in GLBP from
HSRP is that it provides for load balancing between the redundant routers. It load balances
by using a single virtual IP address and multiple virtual MAC addresses. Each host is con-
figured with the same virtual IP address, and all routers in the virtual router group partici-
pate in forwarding packets. GLBP members communicate between each other through
hello messages sent every three seconds to the multicast address 224.0.0.102, User Data-
gram Protocol (UDP) port 3222. GLBP benefits include
Load sharing:
GLBP can be configured in a way that traffic from LAN clients can be
shared by multiple routers.
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Multiple virtual routers:
GLBP supports up to 1024 virtual routers (GLBP groups)
on each physical interface of a router.
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Preemption:
GLBP enables you to preempt an active virtual gateway with a higher-
priority backup.
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Authentication:
Simple text password authentication is supported.
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Server Redundancy
Some environments need fully redundant (mirrored) file and application servers. For exam-
ple, in a brokerage firm where traders must access data to buy and sell stocks, two or more
redundant servers can replicate the data. Also, you can deploy Cisco Unified Communica-
tions Manager (CUCM) servers in clusters for redundancy. The servers should be on differ-
ent networks and use redundant power supplies. To provide high availability in the server
farm module, you have the following options:
Single attachment:
nisms (HSRP, GLBP) to dynamically find alternate router.
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