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C H A P T E R 9 Enterprise Standby Router Protocol
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address or IPX NetID. It is possible for one switch to be master for
one or more VLANs while being in standby for others, thus
allowing the load to be split across participating switches.
If you configure OSPF and ESRP, you must manually configure an
OSPF router identifier (ID). Be sure that you configure a unique
OSPF router ID on each switch running ESRP. For more
information on configuring OSPF, refer to Chapter 11.
To have two or more switches participate in ESRP, the following
must be true:
• For each VLAN to be made redundant, the switches must have the
ability to exchange packets on the same layer 2 broadcast domain
for that VLAN. Multiple paths of exchange can be used, and
typically exist in most network system designs that take
advantage of ESRP.
• In order for a VLAN to be recognized as participating in ESRP,
the assigned IP address or the IPX NETid for the separate
switches must be
identical . Other aspects of the VLAN, including
its name, are ignored.
• ESRP must be enabled on the desired VLANs for each switch.
ESRP cannot be enabled on the VLAN default.
• Enterprise Discovery Protocol (EDP) must be enabled on the
ports that are members of the ESRP VLANs (The default setting
is enabled.).
To verify EDP status, use the following command:
show ports <portlist> info {detail}
Determining the ESRP Master
The ESRP master switch (providing layer 3 routing and/or layer 2
switching services for a VLAN) is determined by the following
factors:
• Active ports —The switch that has the greatest number of active
ports takes highest precedence. A load-sharing port group is
considered a single port.
• Tracking information — In a typical Layer 3 router redundancy
configuration (in which the ESRP switches are routing to a
"cloud" or router backbone), you can use the VLAN that links the