Layer 3 Routing | 24717Layer 3 RoutingThis chapter contains these major sections:• Enabling Routing on page 248• IGMP Proxy on page 251• RIP Configuration on page 255• OSPF Configuration on page 257• VLAN Routing on page 262• Link Aggregation on page 269• Virtual Router Redundancy Protocol on page 271This chapter provides examples of how to use the routing features provided in the SFTOS Layer 3 Package(available only for some S-Series models) to configure your S-Series in some typical network scenarios.The examples begin with support for port routing in a simple network, and explain how to activate themost common routing protocols. A discussion of the use of VLANs with and without VLAN routing isfollowed by sections on Link Aggregation and Virtual Router Redundancy Protocol. For an introduction tothe use of services related to Layer 3, such as Access Control Lists and Differentiated Services, see theirspecific chapters in this guide.An end station specifies the destination station’s Layer 3 address in the packet’s IP header, but sends thepacket to the MAC address of a router. When the Layer 3 router receives the packet, it will minimally:• Look up the Layer 3 address in its address table to determine the outbound port• Update the Layer 3 header• Recreate the Layer 2 headerThe router’s IP address is often statically configured in the end station, although the S-Series supportsprotocols such as DHCP that allow the address to be assigned dynamically. Likewise, you may assignsome of the entries in the routing tables used by the router statically, but protocols such as RIP and OSPFallow the tables to be created and updated dynamically as the network configuration changes.Note: ECMP (Equal Cost Multi-path Routing) is supported for OSPF, not for RIP.2048 IP routes of the 3072 routes that are supported by SFTOS can be ECMP routes.6 ECMP paths are supported.Load balancing is provided automatically by a hash algorithm that is based on an XOR (eXclusive OR) ofthe 3 LSBs (Least Significant Bits) of the source and destination IP addresses.Use the maximum-paths command to set the number of paths. For details, see the maximum-pathscommand in Chapter 20, “OSPF Commands”, of the SFTOS Command Reference Guide.
