On Tuesday, December 10, 2013 10:42:34 AM Patrick M. Hausen wrote: > This enables OSPF on the link to my other router *only*. > OSPF does not by default redistribute connected or > static routes. The 0.0.0.0 looks insane but keep in mind > that it’s an inverted (wildcard) mask so essentially it > says /32.
I have ran OSPF (and sometimes still teach it, although I
teach and run IS-IS more, nowadays), I just haven't ran it
on Junos or IOS XR platforms :-).
> I’ve been doing OSPF for quite some years and IMHO this
> is a perfectly valid and sane way to run an ISP with
> subscriber lines. And I know more than one competitor
> (friendly competition ;-) doing exactly the same.
>
>
> Now … as far as I found out yesterday …
>
> IS-IS *does* by default redistribute connected subnets
> even if they are on passive interfaces. Unless you use
>
> > no isis advertise-prefix
>
> on the interface level.
I don't do much with IS-IS (keep it really simple), but yes,
"passive-interface" in IS-IS and OSPF behave differently in
IOS, as I mentioned before. I'm not sure whether this is the
spec. or something specific to Cisco, as I've only
experienced this on IOS.
"passive-interface" in IS-IS basically means:
- If an interface is defined as passive.
- Advertise whatever IP address is on it.
- But don't run IS-IS on it.
> For static subnets it’s the same as with OSPF. I can
> perfectly live with that, now that I know. I’m just
> wondering what the „redistribute connected“ command is
> for in the context of IS-IS, anyway ;-)
In essence, you're right, "redistribute connected" in IS-IS
is the same as doing "passive-interface" :-).
What I would do, if it were my network, is carry the
customer's /29 in iBGP, rather than the IGP. This scales
better, and any volatility on the customer's link is handled
better by your network since BGP oscillates in much more
controlled manner than an link state IGP would.
Cheers,
Mark.
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