pppd constantly demand dialing - PPP

This is a discussion on pppd constantly demand dialing - PPP ; I have pppd 2.4.4b1 set up on Linux 2.6.12 with demand dialing enabled and it seems to try to keep the link up constantly, even when there's nothing to send. When I disconnect on the other end, it redials. I'll ...

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Thread: pppd constantly demand dialing

  1. pppd constantly demand dialing

    I have pppd 2.4.4b1 set up on Linux 2.6.12 with demand dialing enabled
    and it seems to try to keep the link up constantly, even when there's
    nothing to send. When I disconnect on the other end, it redials. I'll
    dig for details tomorrow but thought I'd shoot this out to see if this
    sounded familar to any one. Thanks in advance for any pointers.

    Chris


  2. Re: pppd constantly demand dialing

    Hello,

    Chris Nelson a écrit :
    > I have pppd 2.4.4b1 set up on Linux 2.6.12 with demand dialing enabled
    > and it seems to try to keep the link up constantly, even when there's
    > nothing to send.


    Are you sure there is no traffic at all on the link, neither transmitted
    nor received ?

    > When I disconnect on the other end, it redials.


    That sounds consistent with pppd's manpage :

    The demand option implies the persist option. If
    this behaviour is not desired, use the nopersist
    option after the demand option. The idle and hold*
    off options are also useful in conjuction with the
    demand option.

  3. Re: pppd constantly demand dialing

    Pascal Hambourg wrote:
    > Chris Nelson a écrit :
    > > I have pppd 2.4.4b1 set up on Linux 2.6.12 with demand dialing enabled
    > > and it seems to try to keep the link up constantly, even when there's
    > > nothing to send.

    >
    > Are you sure there is no traffic at all on the link, neither transmitted
    > nor received ?


    Certainly _received_ data would cause demand dialing, would it? ;-)
    I'm not 100% sure that there is no data to be sent but I haven't been
    able to figure out what might be sending.

    > > When I disconnect on the other end, it redials.

    >
    > That sounds consistent with pppd's manpage :
    >
    > The demand option implies the persist option. If
    > this behaviour is not desired, use the nopersist
    > option after the demand option. The idle and hold*
    > off options are also useful in conjuction with the
    > demand option.


    Yes, I agree.


  4. Re: pppd constantly demand dialing

    Chris Nelson a écrit :
    > Pascal Hambourg wrote:
    >
    >>Chris Nelson a écrit :
    >>
    >>>I have pppd 2.4.4b1 set up on Linux 2.6.12 with demand dialing enabled
    >>>and it seems to try to keep the link up constantly, even when there's
    >>>nothing to send.

    >>
    >>Are you sure there is no traffic at all on the link, neither transmitted
    >>nor received ?

    >
    > Certainly _received_ data would cause demand dialing, would it? ;-)


    Do you mean that as soon as pppd is launched, it establishes the link ?
    I didn't understand this, and instead thought pppd never released the
    link once established.

    > I'm not 100% sure that there is no data to be sent but I haven't been
    > able to figure out what might be sending.


    What about having tcpdump or ethereal listening on the PPP interface and
    watching what's going on ?

  5. Re: pppd constantly demand dialing

    Pascal Hambourg wrote:
    > Chris Nelson a écrit :
    > > Pascal Hambourg wrote:
    > >>Chris Nelson a écrit :
    > >>
    > >>>I have pppd 2.4.4b1 set up on Linux 2.6.12 with demand dialing enabled
    > >>>and it seems to try to keep the link up constantly, even when there's
    > >>>nothing to send.
    > >>
    > >>Are you sure there is no traffic at all on the link, neither transmitted
    > >>nor received ?

    > >
    > > Certainly _received_ data would cause demand dialing, would it? ;-)

    >
    > Do you mean that as soon as pppd is launched, it establishes the link ?
    > I didn't understand this, and instead thought pppd never released the
    > link once established.


    Yes, pppd dials as soon as it's launched. I found that RIP got
    misconfigured to be active on ppp0. Taking that out fixes the problem.

    > > I'm not 100% sure that there is no data to be sent but I haven't been
    > > able to figure out what might be sending.

    >
    > What about having tcpdump or ethereal listening on the PPP interface and
    > watching what's going on ?


    See above.


  6. Re: pppd constantly demand dialing

    "Chris Nelson" writes:

    >I have pppd 2.4.4b1 set up on Linux 2.6.12 with demand dialing enabled
    >and it seems to try to keep the link up constantly, even when there's
    >nothing to send. When I disconnect on the other end, it redials. I'll
    >dig for details tomorrow but thought I'd shoot this out to see if this
    >sounded familar to any one. Thanks in advance for any pointers.


    Something on your end is probably sending out packets onto the web. Check
    your programs. Do a tcpdump on the interface to see what is going out
    every 5 sec or minute, even when everything is supposed to be quiet.
    Ie, I doubt this is a ppp problem. Rather a computer setup problem.



  7. Re: pppd constantly demand dialing

    "Chris Nelson" writes:

    >Pascal Hambourg wrote:
    >> Chris Nelson a =E9crit :
    >> > I have pppd 2.4.4b1 set up on Linux 2.6.12 with demand dialing enabled
    >> > and it seems to try to keep the link up constantly, even when there's
    >> > nothing to send.

    >>
    >> Are you sure there is no traffic at all on the link, neither transmitted
    >> nor received ?


    >Certainly _received_ data would cause demand dialing, would it? ;-)
    >I'm not 100% sure that there is no data to be sent but I haven't been
    >able to figure out what might be sending.



    No. received datat will NOT cause demand dialing, since your machine has no
    idea that the data is there to be received.

    >> > When I disconnect on the other end, it redials.

    >>
    >> That sounds consistent with pppd's manpage :
    >>
    >> The demand option implies the persist option. If
    >> this behaviour is not desired, use the nopersist
    >> option after the demand option. The idle and hold=AD
    >> off options are also useful in conjuction with the
    >> demand option.


    >Yes, I agree.



    So demand will allow timeout to occur. After the timeout, it will wait for
    stuff to be sent.



  8. Re: pppd constantly demand dialing


    Unruh wrote:
    > "Chris Nelson" writes:
    >
    > >I have pppd 2.4.4b1 set up on Linux 2.6.12 with demand dialing enabled
    > >and it seems to try to keep the link up constantly, even when there's
    > >nothing to send. When I disconnect on the other end, it redials. I'll
    > >dig for details tomorrow but thought I'd shoot this out to see if this
    > >sounded familar to any one. Thanks in advance for any pointers.

    >
    > Something on your end is probably sending out packets onto the web. Check
    > your programs. Do a tcpdump on the interface to see what is going out
    > every 5 sec or minute, even when everything is supposed to be quiet.
    > Ie, I doubt this is a ppp problem. Rather a computer setup problem.


    I've rebuilt pppd with PPP_FILTER and have set active-filter to "udp
    port route" (which I think is supposed to exclude RIP) but my switch
    still dials when I have RIP enabled and doesn't when I don't.

    RIP or otherwise, is there conventional wisdom on what active-filter is
    general workable? Or is it too application-specific?


  9. Re: pppd constantly demand dialing

    Chris Nelson wrote:
    > ...
    > I've rebuilt pppd with PPP_FILTER and have set active-filter to "udp
    > port route" (which I think is supposed to exclude RIP) but my switch
    > still dials when I have RIP enabled and doesn't when I don't.
    > ...


    Have I got this backwards? I thought that what I specified for
    active-filter was filtered OUT of consideration for demand dialing but
    re-reading the pppd man page I can see that it might be interpreted as
    specifying only the packets that will be considered, not those that are
    excluded.


  10. Re: pppd constantly demand dialing

    Chris Nelson a écrit :
    > Chris Nelson wrote:
    >
    >>I've rebuilt pppd with PPP_FILTER and have set active-filter to "udp
    >>port route" (which I think is supposed to exclude RIP) but my switch
    >>still dials when I have RIP enabled and doesn't when I don't.

    >
    > Have I got this backwards? I thought that what I specified for
    > active-filter was filtered OUT of consideration for demand dialing but
    > re-reading the pppd man page I can see that it might be interpreted as
    > specifying only the packets that will be considered, not those that are
    > excluded.


    Although I've never used active-filter, I agree with your second
    reading. So you may invert your expression by prefixing it with 'not'.
    I just wonder why you need RIP over the PPP link. Didn't you say that it
    was a mistake ?

  11. Re: pppd constantly demand dialing

    Pascal Hambourg wrote:
    > Chris Nelson a écrit :
    > ...
    > Although I've never used active-filter, I agree with your second
    > reading. So you may invert your expression by prefixing it with 'not'.


    Thanks. I'll try that.

    > I just wonder why you need RIP over the PPP link. Didn't you say that it
    > was a mistake ?


    I've gone back and forth on this issue and honestly I'm still not sure
    I _need_ RIP but I want it as an option. I believe -- and I'm weak on
    RIP -- that it'll allow two systems which do RIP, reside on LANs and
    are connected via PPP to connect systems on the respective LANs. At
    least that's my goal.


  12. Re: pppd constantly demand dialing

    "Chris Nelson" writes:
    > Chris Nelson wrote:
    > > ...
    > > I've rebuilt pppd with PPP_FILTER and have set active-filter to "udp
    > > port route" (which I think is supposed to exclude RIP) but my switch
    > > still dials when I have RIP enabled and doesn't when I don't.
    > > ...

    >
    > Have I got this backwards? I thought that what I specified for
    > active-filter was filtered OUT of consideration for demand dialing but
    > re-reading the pppd man page I can see that it might be interpreted as
    > specifying only the packets that will be considered, not those that are
    > excluded.


    Yes, that's backwards. The "active-filter" determines what
    network-layer things are considered to be activity -- those that match
    are considered activity, and all else is not. The default (with no
    filter) is that all network-layer traffic is considered to be
    "activity."

    --
    James Carlson, KISS Network
    Sun Microsystems / 1 Network Drive 71.232W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677

  13. Re: pppd constantly demand dialing

    James Carlson wrote:
    > ... The "active-filter" determines what
    > network-layer things are considered to be activity -- those that match
    > are considered activity, and all else is not. The default (with no
    > filter) is that all network-layer traffic is considered to be
    > "activity."


    Thanks for the confirmation. Because Zebra's ripd sends a group
    membership on startup, just filtering rip packets wasn't enough. I
    ended up with:

    active-filter '(not (udp port route)) and (not igmp)'


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