3Com 4007, Implementation Manual, Page: 405 / 684

VRRP and Other Networking Operations 405
Spanning Tree
Protocol (STP)
Figure 46 earlier in this chapter shows how you can set up VRRP parallel
routers to provide total redundancy in your inter-LAN operations.
However, because VRRP uses MAC addresses in its advertisements, this
topology can represent a bridge loop to STP. In this parallel topology,
VRRP advertisements must go out on the network in AllClosed mode with
IgnoreSTP (Ignore Spanning Tree Mode)
enabled .
Carefully evaluate your bridging and routing topologies before you
incorporate VRRP into your network operations.
Dynamic Routing
Protocols (RIP, RIP-2,
OSPF)
The dynamic routing protocols RIP, RIP-2, and OSPF have their own
facilities to track routes across networks. You can continue to use these
protocols with VRRP routers, but on any given subnetwork, you must
configure the same routing protocols with the same parameters.
Figure 47 shows how, in a parallel routing environment, OSPF is
configured on each interface in the 99.99.1.0 subnetwork, and RIP-2 is
configured on each interface in the 99.99.2.0 subnetwork. The device AA
has a gateway of Router A.
If Router A becomes unavailable, Router B can take over because the
99.99.1.0 subnetwork has OSPF configured for each routing interface. If,
however, dynamic routing protocols are configured on a router-per-router
basis, so that Router B had RIP-2 configured on the router’s interface to
the 99.99.1.0 subnetwork, the gateway becomes unavailable because of
a dynamic routing protocol mismatch.