DNS doesn't Dial-on-demand

DNS doesn't Dial-on-demand

Post by T. Feis » Mon, 10 Jul 2000 04:00:00



Greetings.
I appear to be having a few problems with the setting up of a DNS.  We have
a reasonably sized network
of ~150 machines, and have a local DNS which does lookups for those, and
passes the rest out onto the
net.  This is not the problem, this bit works fine.  The problem being that
the DNS query to the outside
world doesn't force the router (A cisco 761, with demand set to threshold 0,
time 0 ) to dial and connect.
Any suggestions for why it won't call? (is this a router config problem, or
networking problem?)
All I can think of is that the router requires a tcp request to dial (afaik
DNS is udp?)

So far, my idea is to have ipchains log requests for dns lookup, and have
some monitor script ping a known
outside to force the connection whenever the dns does stuff. The problem
with this is that is the link is already
up, its pointless.

Anyway. If anyone can help, i'd really like to hear about it.  I doubt any
suggestions could be much worse than mine
Thanks in advance

Tom Feist
--
Linux Newbie. Sysadmin wannabe. Monkey for hire.
tom-at-bisti-dot-globalnet-dot-co-dot-uk

 
 
 

DNS doesn't Dial-on-demand

Post by Q » Mon, 10 Jul 2000 04:00:00


I have only had the opportunity to deal with a couple of Cisco routers, but
in my experience it takes a big packet to cause the router to dial.  I can't
remember what I was exactly trying to do, but whatever it was the packet
wasn't big enough or didn't repeat enough.  Is there any way to set the
router to a permanent switched config so it will stay up all the time and
redial if the link goes down?


Quote:> Greetings.
> I appear to be having a few problems with the setting up of a DNS.  We
have
> a reasonably sized network
> of ~150 machines, and have a local DNS which does lookups for those, and
> passes the rest out onto the
> net.  This is not the problem, this bit works fine.  The problem being
that
> the DNS query to the outside
> world doesn't force the router (A cisco 761, with demand set to threshold
0,
> time 0 ) to dial and connect.
> Any suggestions for why it won't call? (is this a router config problem,
or
> networking problem?)
> All I can think of is that the router requires a tcp request to dial
(afaik
> DNS is udp?)

> So far, my idea is to have ipchains log requests for dns lookup, and have
> some monitor script ping a known
> outside to force the connection whenever the dns does stuff. The problem
> with this is that is the link is already
> up, its pointless.

> Anyway. If anyone can help, i'd really like to hear about it.  I doubt any
> suggestions could be much worse than mine
> Thanks in advance

> Tom Feist
> --
> Linux Newbie. Sysadmin wannabe. Monkey for hire.
> tom-at-bisti-dot-globalnet-dot-co-dot-uk


 
 
 

DNS doesn't Dial-on-demand

Post by T. Feis » Tue, 11 Jul 2000 04:00:00



Quote:> I have only had the opportunity to deal with a couple of Cisco routers,
but
> in my experience it takes a big packet to cause the router to dial.  I
can't
> remember what I was exactly trying to do, but whatever it was the packet
> wasn't big enough or didn't repeat enough.  Is there any way to set the
> router to a permanent switched config so it will stay up all the time and
> redial if the link goes down?

From assorted fiddlings, I'm reasonably sure that a permanent link would be
possible.
The only problem is the costs involved.  Here in .uk, we're paying something
like 3 pence
per minute per channel during office hours, which is when the line gets used
the most.
Hence the dial-on-demand to try and minimise the time connected.

On a side note, is there any way to check if the router is connected to the
net, without
something like pinging an external ip? ( which would cause it to dial
regardless, and
not give a proper answer)

Cheers again

Tom Feist
--
Linux Newbie.  Sysadmin Wannabe. Monkey for hire.
tom-at-bisti-dot-globalnet-dot-co-dot-uk

 
 
 

DNS doesn't Dial-on-demand

Post by Q » Tue, 11 Jul 2000 04:00:00


If I remember correctly, you can do something like show isdn status or
something similar.  I think you can do show isdn ?, but it's been a while.




> > I have only had the opportunity to deal with a couple of Cisco routers,
> but
> > in my experience it takes a big packet to cause the router to dial.  I
> can't
> > remember what I was exactly trying to do, but whatever it was the packet
> > wasn't big enough or didn't repeat enough.  Is there any way to set the
> > router to a permanent switched config so it will stay up all the time
and
> > redial if the link goes down?

> From assorted fiddlings, I'm reasonably sure that a permanent link would
be
> possible.
> The only problem is the costs involved.  Here in .uk, we're paying
something
> like 3 pence
> per minute per channel during office hours, which is when the line gets
used
> the most.
> Hence the dial-on-demand to try and minimise the time connected.

> On a side note, is there any way to check if the router is connected to
the
> net, without
> something like pinging an external ip? ( which would cause it to dial
> regardless, and
> not give a proper answer)

> Cheers again

> Tom Feist
> --
> Linux Newbie.  Sysadmin Wannabe. Monkey for hire.
> tom-at-bisti-dot-globalnet-dot-co-dot-uk

 
 
 

1. ISDN Dial-On-Demand: Can't Stop dial with arp packets...

Hello again everybody,

I have installed linux 2.0.30 (Slackware 3.3) on a machine located
remotely from my office connected with ISDN dial-on-demand modem.   I
have diagnosed the dial-out of this machine with TCPDUMP to see why the
machine is dialing out for no reason every 6 minutes or so.

This is the packet that is received from tcp dump from remote host
(durham).

15:28:08.980232 arp who-has ryno.cit-llc.com tell durham.cit-llc.com

ryno is another linux machine on my LAN and durham is the machine on the
remote end that I would like to prevent from dialing out when this
happens.

Now, I ran into a similar problem in a previous version of linux and
modified the /usr/src/linux/net/ipv4/arp.c file and recompiling and
restarting the new kernel.  This has not worked yet as I have tried
different values for the ARP_TIMEOUT and other variables in that file.

Not sure how I can prevent this dial-out from the remote machine.
In case it matters the ISDN boxes that I use are from COMBINET now owned
by Cisco.  Maybe I can filter ARP packets from the ISDN modem?

All help is greatly appreciated.  (I need to save money on this phone
bill).

TIA

Jim Valavanis

--
____________________________________________________________________


  \   Kessler/Asher Group at     |   Whois: JV208                /
   \  the CBOE                   |   phone (312)786-4779        /
    ______  _______  _________       __        __       ______
   / ____/ /__  __/ /___  ___/      / /       / /      / ____/
  / /        / /       / /  _____  / /       / /      / /
 / /____  __/ /__     / /  /____/ / /_____  / /____  / /____
/______/ /______/    /_/         /_______/ /______/ /______/

2. tooltalk error messages

3. Sendmail, DNS, Dial-on-demand

4. Kermit for Solaris

5. pppd 2.3.5 dial-on-demand: first DNS lookup always times out

6. Xconfig problem

7. dial-on-demand, masquerading and DNS issues

8. upgrade

9. linux 2.018/kerneld/PPP dial on demand: 'network unreachable' then starts dialling

10. pppd -d just doesn't demand dial????

11. demand dialing vs. the other demand dialing

12. PPP dial-on-demand woes and other q's

13. Spppcontrol isdn dial-on-demand won't work