In January I described how I configured my Cisco 2651XM router to pass traffic between two VLANs on my Cisco 2950T-24 switch. Today I decided to try upgrading the switch IOS, but that required applying a management IP to the switch. Because switches do not receive IPs on individual ports, I applied the IP to VLAN 1:Unfortunately, this did not work. I could not reach the router from the switch and vice-versa. I think the wrinkle in my setup involves the router.”]
Source: https://taosecurity.blogspot.com/2005/03/switch-to-router-on-stick.html