Ursalink UR75 Edge, User Manual

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UR75 User Guide
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Negative Delay (s)
When interface is down or SLA probing fails, it
will wait according to the time set here before
actually changing its status to Down. Range:
0-180 (0 refers to immediate switching).
0
Positive Delay (s)
When failure recovery occurs, it will wait
according to the time set here before actually
changing its status to Up. Range: 0-180 (0
refers to immediate switching).
1
Table 4-2-6-2 Track Parameters
4.2.6.3 VRRP
The Virtual Router Redundancy Protocol (VRRP) is a computer networking protocol that provides
automatic assignment of available Internet Protocol (IP) routers for participating hosts. This increases the
availability and reliability of routing paths via automatic default gateway selections in an IP sub-network.
Increasing the number of exit gateway is a common method for improving system reliability. VRRP adds a
group of routers that undertake gateway function into a backup group so as to form a virtual router. The
election mechanism of VRRP will decide which router undertakes the forwarding task, and the host in LAN
is only required to configure the default gateway for the virtual router.
In VRRP, routers need to be aware of failures in the virtual master router. To achieve this, the virtual
master router sends out multicast “alive” announcements to the virtual backup routers in the same VRRP
group.
The VRRP router who has the highest number will become the virtual master router. The VRRP router
number ranges from 1 to 255 and usually we use 255 for the highest priority and 100 for backup.
If the current virtual master router receives an announcement from a group member (Router ID) with a
higher priority, then the latter will pre-empt and become the virtual master router.
VRRP has the following characteristics:
- The virtual router with an IP address is known as the Virtual IP address. For the host in LAN, it is only
required to know the IP address of virtual router, and set it as the address of the next hop of the
default route.
- The network Host communicates with the external network through this virtual router.
- A router will be selected from the set of routers based on its priority to undertake the gateway
function. Other routers will be used as backup routers to perform the duties of gateway for the
gateway router in the case of any malfunction, so as to guarantee uninterrupted communication
between the host and external network.
When interface connected with the uplink is at the state of Down or Removed, the router actively lowers
its priority so that priority of other routers in the backup group will be higher. Thus the router with the
highest priority becomes the gateway for the transmission task.