I am working on a strange problem here : there is a switch (Catalyst 2950-24, IOS 12.1(9)EA1) that "forgets" the MAC address table entry of another switch (same type and IOS), despite the direct connection between the two (EtherChannel including Fe0/23 and Fe0/24).
The effects are quite nasty : any IP interaction (a ping, for example) with the VLAN1 produces a flooding of packets, which are eventually destructed due to TTL expired. By so, many packets which should be switched get discarded.
The problem has appeared on 2 of my LANs recently, without any structural change or upgrade. After boot or a direct ping between the 2 switches, the situation is OK as long as the MAC address table keeps the entry. The problem appears after a moment, which seems to equal the MAC address table aging time.
A quick fix that works is to set a static Mac Address Table entry ("mac-address-table static" command), but it remains quick & dirty.
Besides, I would really like to understand what can make Mac Address auto-learning fail like this. Any idea ?
(other technologies involved at LAN level are STP and HSRP)