[c-nsp] C6500 IPv6 redistribute with route-map?

[Patrick M. Hausen]

Morning,

Am 09.12.2013 um 16:26 schrieb Mark Tinka <mark.tinka at seacom.mu>:
> On Monday, December 09, 2013 03:05:17 PM Patrick M. Hausen 
> wrote:
> 
>> Just to make sure i would not accidentally inject
>> anything not belonging to my AS into my IGP.
> 
> Why would you, if you're running IS-IS only on your internal 
> links?

I do. You asked quite a few questions so instead of answering every single one
I will try to summarize where I come from (OSPF) and what I intended to do with IS-IS.

OK, picture two or more routers connected by some link (Ethernet) and each of them with
some number of external links to customers (DSL/ATM in my case):

> int fa0
>  description internal link to neighbor router
>  ip address 192.168.0.1 255.255.255.252
> 
> router ospf 1
>  passive-interface default
>  no passive interface fa0
>  network 192.168.0.1 0.0.0.0 area 0

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.

Now we add a link to a customer:

> int ATM2/0.100 point-to-point
>  description customer’s DSL
>  ip unnumbered fa0
>  pvc 1/100

In reality I use a loopback interface for the unnumbered interfaces, of course.

No we only need to route the customer’s /29.

> ip route 192.168.1.64 255.255.255.248 ATM2/0.100

Because of the very narrow configuration of the OSPF process I never need to
worry about accidentaly running my IGP on a customer’s link. All I need to
distribute that prefix across my network is:

> router ospf 1
>  redistribute static subnets


Now a different layer 2 carrier and slightly different configuration for essentially
the same effect but with bridged instead of routed PVCs:

> int ATM1/0.100 point-to-point
>  description different DSL
>  ip address 192.168.1.73 255.255.255.248
>  atm route-bridged ip
>  pvc 1/100
>   encapsulation aal5snap

To distribute this I need

> router ospf 1
>  redistribute connected subnets

because OSPF does not by default redistribute connected passive interfaces.

But possibly this router runs an external BGP link with an adress belonging
to a different AS on *some* interface. Or an RFC 1918 address somewhere for
out of band management [1]. So in reality it is:

> router ospf 1
>  redistribute connected subnets route-map redistribute-ospf


With the route map restricting routes to my own /20 as I tried to do with IS-IS.

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.

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 ;-)

Kind regards
Patrick

[1] getting rid of them currently in favor of official adresses and tight access-lists
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