ISDN Problem when IP CEF/Fast Switching enabled

Unanswered Question
Dec 20th, 2008
User Badges:


I am on a ISDN dial to a remote router.

I encountered a problem whereby I cannot see the LAN segment over the remote router when CEF & fast switching are enabled on both the dialer & gigaEthernet interface. However, when CEF & Fastswitching are disabled on both the dialer & ethernet, it works fine. Have any1 encounter the similar?

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Giuseppe Larosa Sat, 12/20/2008 - 23:54
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

Hello Lum,

you should provide more details to get better help:

a) platform : what model is your router ?

b) IOS version

c) configuration of dialer, isdn and DDR

In general, in some specific rare cases I saw the need to disable CEF or fast switching usually with IPSec and NAT, but be aware that this has an impact on router performance.

What happens if you disable CEF and fast switching only on the dialer ?

Hope to help



This Discussion