Here is the scenerio: 2 Catalyst 1912 switches connected with 100 Mbits port and set up for trunking. 6 Vlans set up on both swithes, 2 ports to a VLAN. 2 workstations 10.0.4.10/22 10.0.4.11/22. If wkstA and WkstB are in same VLAN on same switch they can ping. If wkstA and WkstB are in same VLAN on second switch they can ping. Now here is where it gets weird. If you move one of the worksations out of the VLAN on a single switch they can't ping(expected). If you are on seperate switches but in the same VLAN and ping 10.0.4.11 -t , then move the workstation to another VLAN on the switch they can still ping(not expected). My thoughts were that there must be some kind of cache on the trunk port that has source MAC's(Workstation's) associated with ISL tags. By moving the workstation to another port in a different VLAN, you still had the same source MAC and therefore would be tagged by ISL as still being in the previous VLAN and would therefore be forwarded to the port in the previous VLAN. Kinda like MLS cache flows. By doing a shut and no shut on the trunk interface or disconnecting and connecting the cable you were not able to ping so I figure the cache was cleared. Has anyone seen this on the higher end switches? Things that make you say HMMMMMM.
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