Hi i have 2 cisco routers 2621 attached with serial port and 1 router is also connected with pc. The problem is that i cannot ping router to router.

Why do you need 2 routers & how is that a telnet problem? How do you know when a politician is lying? His mouth is moving.

You can't ping, or telnet, across a serial port (console) connection. You would need both routers plugged in with a network cable. Which is to say, either plugged into each other with a crossover, or both plugged into your PC with network cables. Then and only then would you be able to ping both and telnet into both.

Seems like when you connect serial you can ping but you have to be on a port that has ip assigned. Ping is a poor choice to use also. Playing to the angels Les Paul (1915-2009)