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Juniper Networks/Cisco Systems Switch Interoperability Cookbook

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To verify all switches send traffic only over the spanning tree interfaces in forwarding

state, generate a known quantity of frames from Spirent TestCenter or other source and

compare switch interface packet counters with those sent and received on each interface.

Interfaces in blocking state will receive spanning tree BPDU frames but should transmit

no frames.

To determine convergence time, disable one of the spanning tree interfaces in forwarding

state while offering a known quantity of frames from Spirent TestCenter or other traffic

generator. Convergence time can be derived from frame loss. For example, if Spirent

TestCenter generates traffic at a rate of 1,000 frames per second, each dropped frame is

equivalent to 1 millisecond of convergence time. If the switches drop 47 frames, then

rapid spanning tree convergence time is 47 ms.

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Objective!

To verify interoperability of a multiple spanning tree topology between Juniper and Cisco

switches.

To measure convergence time of a multiple spanning tree topology between Juniper and

Cisco switches after link failure.

Background!

As defined in IEEE specification 802.1s, the multiple spanning tree protocol (MSTP)

adds loop prevention and redundancy on a per-VLAN basis. With MSTP, individual

spanning tree topologies can be configured for each VLAN.

Topology!

This example uses redundant links between two Juniper switches and one Cisco switch.

VLAN IDs of 2001 and 2002 have been defined on both the Juniper and Cisco switches,

and MSTP is enabled on all switches.

Figure 14 illustrates the MSTP validation test bed. This example involves a standalone

Juniper EX4300 switch; a Juniper Virtual Chassis Fabric (comprised of two Juniper

QFX5100 and one Juniper EX4300 switches); and a Cisco Nexus 7010.

As shown in the figure, the links interconnecting each switch are trunk ports that allow

tagged traffic from VLAN IDs 2001 and 2002. Two access-mode ports are configured on

each switch: One apiece for VLAN IDs 2001 and 2002. Traffic offered from the Spirent

TestCenter traffic generator/analyzer verifies the spanning tree topology in each VLAN.

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Cisco Ex SERIES Instrukcja Użytkownika Strona 59