WAN - SVI to Layer 3 question

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Mar 7th, 2008
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Scenerio:-Both locations have Multi Layer Switches. Location "A" -> 100mb FastEthernet, "no switchport", Layer 3 interface, with IP address configured /30 subnet mask. Location "B"-> 100mb FastEthernet Layer 2 interface, "switchport vlan 10" with VLAN10 IP address configured /30 subnet mask. This works ok however !!

What are the disadvantages and advantages of this scenerio from an High Availability and Convergence point of view ?

Thanks in advance.

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Jon Marshall Fri, 03/07/2008 - 06:11
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Main issue is that you are running STP on that link because you are going to an SVI. So a reconvergence within vlan 10 could temporarily affect forwarding.

High availability - none really as it is a single link.


gacunt1964 Fri, 03/07/2008 - 06:33
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Thanks, confirms what I thought. So on the SVI side (Vlan10), you have spanning-tree by default(But, there is only one port in the instance). So with BPDU's and associated timers this can be an restraint?

With "Switchport" configured you use "process" instead on "fast" switching for the F0/0/0 interface. Also with VLAN10 this uses "fast" instead of "process" switching.

From a routing point of view the metric used (by default) is the bandwidth of the VLAN interface(gig) and not the F0/0/0 interface.

Are there any other advantages/disadvantages ?

Is this common practice to use this configuration (i would think not)?


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