Riverbed SteelHead 3070-SD, User Manual

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Configuring Local Subnet Discovery on SteelHead SD | 27
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Configuring Local Subnet Discovery on
SteelHead SD
This topic describes how to configure SteelHead SD to discover global and local subnets on the LAN side
of the network. It includes these topics:
• “Overview of local subnet discovery” on page 27
• “Routing criteria” on page 27
• “Defining global subnet discovery at the organization level” on page 28
• “Defining local subnet discovery” on page 30
These procedures describe local and global subnet autodiscovery for SteelHead SD 570-SD, 770-SD,
and 3070-SD appliances and the SteelConnect SDI-2030 gateway located at the branch. For detailed
information, see the
SteelConnect Manager User Guide .
Overview of local subnet discovery
SteelHead SD provides the ability to discover subnets at the zone and site level in a branch. Local subnet
discovery identifies routes that are local to a particular branch. These routes can be reached from other
sites or branches using the overlay tunnels. Local subnet discovery allows you to define a set of routing
criteria so that routes that match the criteria are qualified as subnets local to the branch.
Ideally, all routes learned over the LAN interfaces of an appliance, on a particular branch, should be
qualified as routes local to that branch. However, this qualification isn't always straight forward. Consider
the case where OSPF is configured with both the LAN zones and the WAN uplinks attached to it. In this
case, OSPF will not be able to differentiate the routes that it learns over the LAN zones from the ones
that it learns over the WAN uplinks.
A similar problem can arise when BGP is the chosen protocol where an iBGP neighbor is established with
the LAN router and an eBGP neighbor is established with the provider-edge router over the WAN uplink.
Here BGP will not be able to call out the local subnets implicitly. Another case to consider is when the
appliance is placed behind a branch router, it loses the notion of LAN zones and WAN uplinks. The local
subnet autodiscovery feature provides a means for identifying subnets that are local to a branch.
Routing criteria
Local subnet discovery allows you to define a set of routing criteria so that routes that match the criteria
are qualified as subnets local to the branch. The routing criteria are: