User guide

10-12 E
XTREME
W
ARE
S
OFTWARE
U
SER
G
UIDE
E
XTREME
S
TANDBY
R
OUTER
P
ROTOCOL
L
INKING
ESRP S
WITCHES
When considering system design using ESRP, direct links between ESRP switches are
useful under the following conditions:
• A direct link can provide a more direct routed path, if the ESRP switches are routing
and supporting multiple VLANs where the master/standby configuration is split
such that one switch is master for some VLANs and a second switch is master for
other VLANs. The direct link can contain a unique router-to-router VLAN/subnet,
sot that the most direct routed path between two VLANs with different master
switches uses a direct link, instead of forwarding through another set of connected
routers.
• A direct link can be used as a highly reliable method to exchange ESRP hellos, so
that the possibility of having multiple masters for the same VLAN is lessened,
should all downstream Layer 2 switches fail.
• A direct link is necessary when the ESRP HA option. The direct link is used to
provide Layer 2 forwarding services through an ESRP standby switch.
Direct links may contain a router-to-router VLAN, along with VLANs running ESRP. If
multiple VLANs are used on the direct links, use 802.1Q tagging. The direct links may
be aggregated into a load-shared group, if desired.
C
ONFIGURING
ESRP
AND
M
ULTINETTING
When configuring ESRP and IP multinetting on the same switch, the parameters that
affect the determination of the ESRP master must be configured identically for all the
VLANs involved with IP multinetting. For example, the number of links in your
configuration, the priority settings, and timer settings must be identical for all affected
VLANs.
ESRP
AND
S
PANNING
T
REE
A switch running ESRP should not simultaneously participate in the Spanning Tree
Protocol (STP) for the same VLAN(s). Other switches in the VLAN being protected by
ESRP may run STP and the switch running ESRP forwards, but does not filter, STP
BPDUs. Therefore, you can combine ESRP and STP on a network and a VLAN, but you
must do so on separate devices. You should be careful to maintain ESRP connectivity
between ESPR master and standby switches when you design a network that uses ESRP
and STP.