I'm currently working at a client site were I have been asked to stabilize a network following a major failure of a portion of it in June of last year. The network is designed as follows:
Two campuses are supported by a network designed with two Gig interlinked (cross campus) core switches (Cisco 6000's one at each site). Each of these two in turn support diverse Gig uplinks to four distribution switches (again Cisco 6000's, two at each site, there are links between pairs of distribution switches at each campus). OSPF is configured in three main area groups across all devices.
Each pair of site distribution switches supports dual uplinks to stacked (up to six maximum, on average four per stack) 3750's at the access layer. The initial task was to replace the supervisor engines on the two failed distribution switch units (one at each campus).
There is a single VTP domain, with approximately 200 vlans in it. All trunk links carried all of the vlans as no âswitchport trunk allowâ statements were applied. Redundant vlan's were removed and relevant âswitchport trunk allowâ statements to each of the trunk uplinks from distribution to access layer as well as within the core were applied.
Both distribution switches are now back on line. The task now is to analyse and optimize the configuration of firstly Spanning Tree (pvst) as it has been shown that the network failure was mainly due to many pvst instances being supported at the access layer. Secondly HSRP. My questions are in relation to spanning tree.
1. STP has elected six root bridges across various access switch stacks and one distribution switch. Is it advisable to leave this configuration as it is, or should I attempt to select the two core switches as primary and secondary root bridges for the VLAN's, is it ok for access switches to be configured as root bridges. What is the best approach to go about this work ??
2. What is the purpose of STP in a layer three environment like this, surely OSPF takes care of redundant links and loops etc ??
3. How can STP cause two supervisor engines to fail at the distribution layer ??
4. Basic Question: why is a native VLAN necessary
5. What is VLAN leakage.