Cisco ISR Routers

ISR ROUTER

An ISR integrates other network features into the router other than just routing features. Used mostly in small offices on ADSL lines, they offer things like VPN, firewall, and encryption services. An example of an ISR is the Cisco 851W.

Cisco's line of integrated services routers (ISRs) provide multiple services, along with high-speed network transmission rates, in one package . Billed as networking without boundaries, these routers provide a higher degree of functionality than an average wireless router. An ISR is a good option for larger businesses that operate in an office setting. This router can replace several other devices by providing numerous functions at once.

VLAN 1 minimization

Generally when a Vlan is removed from the allowed list on a trunk link then all traffic of that vlan are dropped by the switch on that link.
But when Vlan 1 is removed from the allowed list the switch continues to pass some vlan1 traffic like cdp and vtp, only no more user(i.e. data) traffic is passed, this process is VLAN 1 minimization.

VLAN related info ......

Number of Vlan's supported on cisco switches

In general old 2950 switches will support upto 64 vlans and newer 2960 switches will support upto 255 vlans.

When we talk about 64 and 250 vlans it does not mean that you cannot create more than 64 vlans it just means that only 64 vlans will be having per vlan spanning tree instance.

For example 2950 as a VTP client will learn all normal-range VLANs, with VLAN IDs 1 to 1005; VLAN IDs greater than 1005 are extended-range VLANs and are not stored in the VLAN database. The switch must be in VTP transparent mode when you create VLAN IDs from 1006 to 4094.

Again mostly all switches support normal vlans upto 1005 but if we talk of per vlan spanning tree it depends on hardware and also on image it is running.
Like 2950 running standard image only supports 64 per vlan spanning tree and 2950 with enhance image supports upto 250 per vlan spanning tree instance but still both will let you create more than 64 and 250 vlans just that per vlan spanning tree instance will be only supported on 64 and 250 vlans depending upon image they are running.

And in this situation when you have more than 64 vlans on switch running standard image it is recommended not to run PVST+ but to confiure MST.