Area And Subnets; Vrrp Operation - RuggedCom RuggedRouter RX1000 User Manual

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RuggedRouter User Guide

Area And Subnets

As the OSPF design is simple, an area of 0 is used. The three point-to-point T1/E1
links are placed in the area by adding 1.1.1.0/24 to it. Router 1 and 2 will include
their Ethernet links by adding subnet 1.1.2.0/24 to their area descriptions. Router 3
must also include 2.2.2.0/24 in its area description so that its existence is advertised.
The point-to-point T1/E1 interfaces and Ethernet interfaces on Router 1 and 2 must be
made active. The Ethernet interface on Router 3 can be left passive since it does not
participate in OSPF advertisements.
Router 1 and 2 must enable link-detect, to stop advertising 1.1.1.0/24 in the event of a
link failure.

VRRP Operation

Router 1 and 2 have VRRP setup on their Ethernet connection so that they can both
function as the gateway for the clients on their network segment. Normally Router 1
is the VRRP master, and only in case of a link failure to the switch or the router
failing, will Router 2 take over the virtual IP. The virtual IP used as the gateway is
1.1.2.254. Each router also has its own IP on the network so that each can be reached
individually.
If Router 1 or its Ethernet link fail, VRRP will detect the link being down and remove
the direct route to the 1.1.2.0/24. VRRP on Router 2 will stop seeing messages from
Router 1, elect itself master and will take over the gateway for the network.
OSPF on router 1 will notice the link being down (and the route to 1.1.2.0/24
disappearing) and will use information from router 2 install a route to 1.1.2.0/24 via
Router 2.
Router 3 will notice than Router 2 is now a more direct path to 1.1.2.0/24 network and
start sending to Router 2 instead of Router 1.
After the failure all routers still know how to reach the entire network, and the clients
on 1.1.2.0/24 can still send on the network using the same gateway address. The
clients will see only a MAC address change of the gateway and experience a few
seconds of network outage When the link returns, VRRP will switch back to the
master, and the routes will return to their normal state.
Note that if the Router 1 wan link fails, Router will see routes to Router3 via the
Router 1 – Router 2 wan and Ethernet links. If the faster Router 1 – Router 2 Ethernet
path fails, Router 1 will fall back to the Router 1 – Router 2 wan link.
Note that it would not be useful to leave the Ethernet 1.1.2.0/24 subnets out of the
area and turn on redistribute connected as OSPF would not use the subnets for
routing.
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