Re: ISDN preference

[Robert J. McKay <nospam [at] mckay.com>]

On Mon, 24 Jan 2000, Damion Yates wrote:

> sheflug - http://www.sheflug.co.uk
>
> On Mon, 24 Jan 2000, French, Alastair wrote:
>
> > I need to connect a small private network (with a linux box currently acting
> > as a firewall and performing masqerading) via ISDN.
> >
> > As far as I can see I have three options
> >
> > ISDN router, connected via a secondary network card on the linux box
>
> I think this is the most expensive option, you won't be able to use Linux's
> masqerading support, but often routers come with their own NAT, it's possibly
> easier to setup as it's all they are supposed to sit their doing, so the
> instructions will be specific and correct, you'll probably lack support for
> some protocols, like realmedia, irc's DCC and more as they come. Linux's
> masqerading support is good and constantly worked on. This would be a solid
> state system you won't hear if left on all the time.

This isn't really a problem at all. If you want to use NAT on the linux
box instead of the router you can just have the router assign the IP to
the linux box via dhcp and then whenever it connects the linux box gets
the IP directly and you can make it do all the work. The NAT on my router
seems to work fine with realmedia and IRC anyway although I have had
troubles with Netmeeting.

> > External ISDN TA, via serial port on Linux box

> I've done this, I had a crap old 486 and had to get an extra isa serial card
> to be able to do 115200 baud to the isdn box. It was just like a modem to
> the OS, AT caused OK to come back, AT [at] MENU gave a fancy menu (if you like
> that) this meant setting up pppd was trivial (no change from normal modem
> only faster), it was _really_ fast, faster than I thought 64kpbs could give,
> which made me wonder about 56k modems vs 64k ISDN, I'd pretty much say ISDN
> is worth the difference in cost after seeing it in action.

> It did take about 7 seconds before I had reliable tcp/ip to anywhere (dial on
> demand using kerneld's /sbin/request-route system), but as this was much
> faster than a modem I didn't mind the pause.
>
> > Internal ISDN TA in linux box

> This is much more low level, could be more difficult to get working, My dad's
> done this (with some coaching by phone from me, as he's still learning
> Linux), you use a different pppd for synchronous ppp (ipppd).

> You're much closer to the ISDN layers and so have more cool abilities, should
> you want to play with them (you're own ISDN to another owned ISDN in a
> company for example), this is less use for just connecting to an ISP, but you
> could do fancy stuff with CLIP (Caller ID) and suchlike, it's up to you.
> Once setup this is gonna be the same as an external TA, but probably cheaper
> and from what I've heard the connection time can be much faster. If I was
> gonna do ISDN gateways again, I'd use this myself, much more fun and fiddly,
> more control, MUCH cheaper.

Although what you say is true and this option will almost certainly
mean slightly more work it may not be that big a deal.

> You'll need your masqerading Linux box on all the time for the later two,
> that is about the only advantage of using an ISDN router.

He'd need to do that anyway since he's planning to use it as a firewall.
Routers are very reliable, they generally just work that's why I like
them.

> > Something I also need to know is how to do channel bonding (bundling) the
> > router would handle this automatically I would have thought, but what about
> > the others

Yes, routers generally take care of that (mine does you just set one
setting from 64kb to Bandwidth on Demand or 128K with bandwidth on demand
it brings up the second channel after the first one has been fully
saturated for some specified time like 5 seconds). I have no idea how to
do it on an internal or external TA but it's certainly possible. There may
very well be some gotchas there and it probably makes a big difference
what TA you're using.

> You'd need to see which ISP's will support this, all three should work with
> BONDing though.

Most ISPs seem to support it.. Even freeserve does although freeserve's
implementation is pretty poor and only works about 50% of the time.
Nildram works flawlessly and they're a great ISP.

Regards,

Robert McKay.

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