Switch Meshing

Operating Notes for Switch Meshing

C a u t i o n

Because the switch automatically gives faster links a higher priority, the

 

default STP or RSTP parameter settings are usually adequate for spanning tree

 

operation. Because incorrect settings can adversely affect network

 

performance, you should avoid making changes without having a strong

 

understanding of how STP or RSTP operates. For more on STP and RSTP, refer

 

to chapter 13, “802.1w Rapid Spanning Tree Protocol (RSTP) and 802.1d

 

Spanning Tree Protocol”. Also, you may want to examine the IEEE 802.1d or

 

802.1w standard, depending on which version of spanning-tree you are using.

 

 

Filtering/Security in Meshed Switches

Because paths through the mesh can vary with network conditions, configur­ ing filters on meshed ports can create traffic problems that are difficult to predict, and is not recommended. However, configuring filters on non-meshed ports in an edge switch provides you with control and predictability.

IP Multicast (IGMP) in Meshed Switches

Like trunked ports, the switch mesh domain appears as a single port to IGMP. However, unlike trunked ports, IGMP protocol and multicast traffic may be sent out over several links in the mesh in the same manner as broadcast packets.

Static VLANs

In a network having a switch mesh domain and multiple static VLANs config­ ured, all static VLANs must be configured on each meshed switch, even if no ports on the switch are assigned to any VLAN. (The switch mesh is a member of all static VLANs configured on the switches in the mesh.)

When static VLANs are configured, the mesh is seen as a single entity by each VLAN. All ports in the mesh domain are members of all VLANs and can be used to forward traffic for any VLAN. However, the non-mesh ports on edge switches that allow traffic to move between the mesh and non-meshed devices belong to specific VLANs and do not allow packets originating in a specific VLAN to enter non-meshed devices that do not belong to that same VLAN. (It is necessary to use a router to communicate between VLANs.) For example, in the following illustration, traffic from host A entering the switch mesh can only exit the mesh at the port for hosts B and E. Traffic from host A for any other host (such as C or D) will be dropped because only hosts B and E are in the same VLAN as host A.

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