Specifications
Industrial Networking Solutions
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Industrial Ethernet Switches >
Introduction to Managed Ethernet Switches
Layer 3 switches use the IP address to make switching decisions,
just like a router, but use hardware optimized to transmit data just as
fast as Layer 2 switches. The 802.1Q VLAN of a Layer 2 switch allows
network operators to configure and maintain their network more
effectively, but cross VLAN communication still relies on traditional
Layer 3 routers. Both routers and Layer 3 switches use a routing
protocol and routing table to determine the best path. However,
compared to routers, which are usually software-based, Layer 3
switches are relatively faster and less expensive. This is due to their
built-in switching hardware with optimized chips and full-wire speed
IP frame forwarding performance suitable for interconnecting VLANs.
Moxa’s Layer 3 switches can be used to partition a large-scale LAN
into multiple subnets for better network performance.
What is a Layer 3 Switch?
Instead of using MAC tables in the way that Layer 2 Ethernet switches
them, the EDS-828 has a built-in IP routing table to support the
forwarding of IP frames. Network administrators need to configure and
maintain this IP routing table manually, and if changes are made to the
network topology, the network administrator will need to reconfigure
the routing table.
Static Routing
In addition to static routing, the EDS-828 has a built-in IP routing
table that can be set up and updated dynamically by RIP (routing
information protocol). RIP is an often used routing protocol that relies
on the Bellman-Ford algorithm and “hop count” measurement to
determine how packets should be routed from one network to another.
Routing Information Protocol (RIP)
The EDS-828 also supports OSPF (open shortest path first), which
uses “Link State” instead of “hop count” to determine the network
route. OSPF is more complicated than RIP. However, compared to
RIP, OSPF has faster network convergence and results in less network
traffic. Both RIP and OSPF are usually referred to as Interior Gateway
Protocols (IGP).
Open Shortest Path First (OSPF)
LAN A
LAN B
Layer 3
Switch
The EDS-828’s built-in IP routing table can be updated and maintained
both statically and dynamically. If the network is small and fixed, the
network administrator may decide to configure the IP routing table
manually. However, any change in the network topology will require
the network administrator to reconfigure the settings manually. If the
network is extended or the network topology is changed frequently,
using dynamic routing provides an efficient way to enhance network
stability and reduce the time it takes to effect network convergence.
Dynamic routing protocol allows devices to detect and respond to
network changes automatically. In this case, network administrators
do not need to reconfigure the settings after the network changes.
The EDS-828 supports Distance Vector Multicast Routing Protocol
(DVMRP), which is used to share information between routers to
transport IP multicast packets between networks. DVMRP resembles
RIP, but is extended for multicast delivery to forward packets. The
router generates a routing table with the multicast group for which
it knows the corresponding distances. When a multicast packet is
received by a router, it is forwarded by the routing interfaces specified
in the routing table.
The EDS-828 supports the Protocol Independent Multicast—Dense
Mode (PIM-DM), which is designed mainly for multicast LAN
applications with high bandwidth. PIM-DM is optimized to guarantee
delivery of multicast packets so as not to reduce overhead. The PIM-
DM multicast routing protocol assumes that all downstream routers
would like to receive multicast messages, and relies upon explicit
pruning messages from downstream routers to remove branches
from the multicast delivery tree that do not contain multicast group
members. PIM-DM is an efficient protocol since most receivers are
interested in the multicast data, but does not scale well across larger
domains in which most receivers are not interested in the data.
Static versus Dynamic
Distance Vector Multicast Routing Protocol (DVMRP)
Protocol Independent Multicast—Dense Mode (PIM-DM)
Intelligent Layer 3 Network Control