what is the defference between these interfaces? S0, S0/0, S0/0/0
thanks for your urgent reply
If you go back to an old 2500 module, you might see that its serial port in built directly into the box, much as its Ethernet port. So the box has Ethernet 0 and serial 0.
On more recent routers that have replaced the 2500 series such as the 2800 series, serial ports aren't directly built into the box, instead there may be multiple module slots. When you place a multiple port card in such slots (e.g. HWIC-4T, see http://www.cisco.com/en/US/prod/collateral/modules/ps5949/ps6182/product_data_sheet0900aecd80274416.html), to identify an individual port, you need to identify both the slot and the port. One reason for this, i.e. where you just don't number all ports in sequence, since not all modules slots have to be used and when they are used they might host a different number of ports, other port numbers are not impacted.