C-M-G
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Manual
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Chapter 5: Network Configuration
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5.18 VRRP / Loadbalancer *
5.18.1 Functionality VRRP
In this menu you can configure and change VRRP (Virtual Router Redundancy Protocol) units and
dependants.
VRRP means that multiple routers can be employed as virtual default routers. If the so-called master
router fails, the backup router dynamically (i.e. without manual switchover) overtakes the tasks of the
master router. For this, the routers exchange so-called VRRP-Advertisements (RFC3768) with each
other.
5.18.1.1 Behaviour of the VRRP in Backup Status
In backup status the VRRP monitors the master router to see if it is active and whether it is regularly
sending its VRRP Advertisements. In backup status the router behaves as follows:
It is not allowed to answer an ARP request for a virtual IP address
It rejects all IP packets, which have a virtual IP address as target IP address
If the router in backup status receives a VRRP Advertisement with priority 0, or the Master_Down_Timer
runs out, the following will happen:
The router sends its own VRRP Advertisement, in which it announces that it is the new master
It sends an ARP Response to announce the assignment of the virtual IP address to the new MAC
address
The Advertisement Timer is started
The router switches to master status
In case the router (that already has master status) receives another VRRP Advertisement:
With a higher priority, the router returns to the backup status
With a lower priority, the VRRP Advertisement IP packet will be rejected and the router
retains its master status
5.18.1.2 Behaviour of the VRRP-Routers in Master-Status
When the router has master status, it is immediately responsible for the forwarding of IP packets in other
IP subnetworks. Hence, it functions as a default gateway. In master status the route behaves as follows:
It sends VRRP-Advertisements in periodical intervals (normally 1s) to the backup router
It answers requests that correspond to the virtual IP address
In case, where it is not the “IP Address Owner”, it rejects all the IP packets, which have a virtual
IP address as target IP address
If the actual master router receives a VRRP Advertisement:
With higher priority as its own, then the Master_Down_Timer is started and it changes to
backup status.
With lower priority, this VRRP Advertisements will be ignored and rejected.
5.18.2 Global Definitions
Menu to configure email alerts for VRRP, which will always inform users whenever each VRRP instance
switches its state.