PPP default route

One of those readers that prefer to remain anonymous has left an interesting comment to my post “Almost-dynamic routing over ADSL interfaces”:

You do not need the route "ip route 0.0.0.0 0.0.0.0 Dialer0 10 track 100" and the tracking if you configure "ppp ipcp route default" on the dialer interface. Works the same way... :-)
You might be wondering why Cisco's engineers decided to pollute IOS with yet another feature. The problem they had was the way PPP over Frame Relay is implemented: it uses virtual interfaces and although you have a very static connection, you cannot bind a static interface name to it. A dynamic interface (with potentially changing name) is cloned from the virtual template every time the PPP-over-Frame-relay session is started. Obviously you cannot configure a static default route pointing to it in advance, so you need yet another feature to do it (I'll not even try to figure out how to create non-default static routes pointing to cloned interface).

5 comments:

  1. How about PPP over ATM? Can you bind it to interface with static name?

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  2. PPPoA uses the dialer interface like PPPoE or ISDN, so the interface name is configured by the operator.

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  3. But my operator thinking I'm using ATMoUSB :)
    They don't have access to my Cisco box. I put virtual-template into pvc definition and it works.

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  4. When using "ppp ipcp route default" you can't change the default metric of 0. So you can't make a PPP session a backup default route. It's good for PPP as your only or primary external default connection.

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  5. In this case, use any one of the other mechanisms (see also links in the post)

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Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.