Siemens SIMATIC NET System Manual page 47

VRRPv3
Version 3 of VRRP is based on Version 2. VRRPv3 has the following characteristics:
● VRRPv3 supports IPv4 and IPv6. Both can be configured and operated at the same time
with VRRP3.
● Simultaneous operation of VRRPv2 and VRRPv3 is not possible.
● You can only use VRRPv3 in conjunction with VLAN interfaces. Router ports are not
supported.
Dynamic routing with OSPFv2
Open Short Path First is a routing protocol developed by the Internet Engineering Task
Force (IETF). With OSPF, CIDR (Classless Inter-Domain Routing) and VLSM (Variable
Length Subnet Mask) are also implemented.
The routers setup a, neighborhood database (LSDB = Link State DataBase). The
neighborhood database is the heart of OSPF and contains information on the topology of the
network.
To set up the neighborhood database, the router needs to learn its direct neighbor routers.
To do this, the router sends out Hello packets following initialization. The neighbor routers
exchange packets (LSA - Link State Advertisements) that describe the content of their
database. When the exchange of information with the neighbor router is completed the
neighborhood database of the neighbor routers is the same.
The neighborhood database is used to calculate routes based on the SPF algorithm
(Shortest Path First). The algorithm creates a hierarchical tree structure (Shortest Path Tree)
in which each destination with the shortest (loop-free) and most inexpensive route is entered.
The algorithm uses the costs of the path as a metric. The costs can be, for example, the data
rate of the connection or the reliability of the connection. The entries from the tree are
adopted in the routing table. If several routes with the same costs exist for a destination, the
data is transferred via different routes to achieve load distribution.
The routers continuously test the state of the connection between themselves by exchanging
Hello packets. If a connection is disrupted, the router sends a message to its neighbor
router. The neighbor router updates its database and sends the message to its neighbor
router and so on until the modification has passed through the entire network.
To limit the size of the routing table, OSPF can divide a network (autonomous system) into
hierarchical areas. Each area has its own neighborhood database and its own shortest path
tree.
By dividing into areas, if there is change in the topology, the entire network is not loaded with
messages so that OSPF manages with relatively low overheads.
If several neighbor routers can be reached in an area, the designated router (DR) and the
backup designated router (BDR) are identified based on Hello packets. By identifying the
designated router, the topology is simplified. The designated router then sends the message.
To send a frame from area 1 to area 2, the frame is first sent to the area border router (ABR)
of area 1. The ABR connects its area to the backbone area. The ABR of area 1 sends the
frame to the router in the backbone area that forwards the frame to the ABR of area 2. The
backbone area (area 0) is used to distribute routing information about the reachability of
areas between area border routers. A frame is sent to another AS via an Autonomous
Industrial Ethernet
System Manual, 09/2019, C79000-G8976-C242-10
Basics of communication with Industrial Ethernet
1.3 Technologies of Industrial Ethernet
47