IBM RackSwitch G8000, Application Manual

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© Copyright IBM Corp. 2011 Chapter 25. Virtual Router Redundancy Protocol
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Master and Backup Virtual Router
Within each virtual router, one VRRP router is selected to be the virtual router
master. See “Selecting the Master VRRP Router” on page 300 for an explanation of
the selection process.
Note: If the IPv4 address owner is available, it will always become the virtual router
master.
The virtual router master forwards packets sent to the virtual router. It also responds
to Address Resolution Protocol (ARP) requests sent to the virtual router's IPv4
address. Finally, the virtual router master sends out periodic advertisements to let
other VRRP routers know it is alive and its priority.
Within a virtual router, the VRRP routers not selected to be the master are known as
virtual router backups. If the virtual router master fails, one of the virtual router
backups becomes the master and assumes its responsibilities.
Virtual Interface Router
At Layer 3, a Virtual Interface Router (VIR) allows two VRRP routers to share an IP
interface across the routers. VIRs provide a single Destination IPv4 (DIP) address
for upstream routers to reach various destination networks, and provide a virtual
default Gateway.
Note: Every VIR must be assigned to an IP interface, and every IP interface must
be assigned to a VLAN. If no port in a VLAN has link up, the IP interface of
that VLAN is down, and if the IP interface of a VIR is down, that VIR goes
into INIT state.
VRRP Operation
Only the virtual router master responds to ARP requests. Therefore, the upstream
routers only forward packets destined to the master. The master also responds to
ICMP ping requests. The backup does not forward any traffic, nor does it respond to
ARP requests.
If the master is not available, the backup becomes the master and takes over
responsibility for packet forwarding and responding to ARP requests.