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Gateway Redundancy
These are also commonly called first-hop redundancy protocols
(FHRP)because the first router hop is given high availability. Some
of Gateway Redundancy
protocols are
Hot Standby Router Protocol (HSRP)
Virtual Router Redundancy Protocol (VRRP)
Gateway Load Balancing Protocol (GLBP)
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Packet-Forwarding Review
When a host must communicate with a device on its local subnet,
it cangenerate an Address Resolution Protocol (ARP) request, wait
for the ARP reply, and
exchange packets directly.
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Packet-Forwarding Review
However, if the far end is located on a different subnet, the
host must relyon an intermediate system (a router, for example) to
relay packets to and from that
subnet. A host identifies its nearest router, also known as the
default gateway or
next hop, by its IP address. And then, the host first sends an
ARP request to find the
gateways MAC address.
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GLBP Physical Layout
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Single Virtual Gateway for Enterprise Network
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GLBP Physical Layout
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GLBP Routers Group
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GLBP Physical Layout
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Example : 192.168.1.1
Single Virtual Gateway IP
is represented by GLBPRouters
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GLBP Physical Layout
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Example : 192.168.1.1
Single Virtual Gateway IP
is represented by GLBPRouters
Clients ip address setting
IP address 192.168.1.2Subnet Mask 255.255.255.0
Gateway 192.168.1.1
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GLBP More Detail
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Active Virtual Gateway
The trick behind this load balancing lies in the GLBP
group. One router is elected the active virtual gateway
(AVG).
This router has the highest priority value, or the highest
IP
address in the group, if there is no highest priority. The
AVGanswers all ARP requests for the virtual router address.
GLBP group numbers range from 0 to 1023. The router
prioritycan be 1 to 255 (255 is the highest priority),
defaulting
to 100.
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Active Virtual Gateway - AVG
Routers participating in GLBP must monitor each
others presence so that another router can assume the role
of
a failed router. To do this, the AVG sends periodic hello
messages to each of the other GLBP peers. In addition, itexpects
to receive hello messages from each of them.
GLBP Hello Interval 3 seconds
GLBP Holdtime 10 seconds
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Active Virtual Forwarder - AVF
Each router participating in the GLBP group canbecome an AVF, if
the AVG assigns it hat role, along with avirtual MAC address. The
virtual MAC addresses always havethe form 0007.b4xx.xxyy. The
16-bit value denoted by xx.xx
represents six zero bits followed by a 10-bit GLBP groupnumber.
The 8-bit yy value is the virtual forwarder number.
Example 0007.b400.0101
0007.b4 = default00.01 = GLBP group number
01 = AVF number
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Active Virtual Forwarder - AVF
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5/8/2013 13ACH Network Professional Training Center
Now Lets Start Practical
..!!!!
