[j-nsp] External routes in OSPF database

[Keegan Holley]

2011/7/9 Alex D. <listensammler at gmx.de>

> Hello,
>
> we have a MPLS enabled backbone with about 30 routers. IS-IS is used as
> IGP. All routers have iBGP sessions with our two route-reflectors and get
> BGP full-feed from them.
> Now i try to setup OSPF with area 0.0.0.0 for connecting customers to one
> of our PE routers (running JUNOS 7.5R2.8).


You should upgrade as soon as possible if your hardware supports it.


> Customer should get only a default route via OSPF.
>

Are you providing internet to your customers?  If you you should use BGP or
static routes.  OSPF neighbors tax resources.  It's also not a good idea to
have all the customer routers and network routers in the same area.
 Topology changes will propogate throughout the entire network which could
cause resource issues at scale.


> Now i have the problem that all BGP routes appear as external routes in
> OSPF database, but only when adjacency to the neighbor router, a Cisco 1841,
> is up.
>

Are you sure that it is all the BGP routes?  If you redistributed the whole
table into OSPF and then advertised it to all 30 routers the network would
probably melt down. (I'm about 85% sure of that) What is the next-hop/router
ID in the routes?  Your probably learning them from the customer.  Also if
the routers weren't coming from the customer they would probably still be
there when you shut down the ospf neighbor with them.  This is another
problem with OSPF it's difficult to filter incoming routes from the
database.  If you plan to use ospf with customers you should implement some
kind of database filter to protect your routers.



> Without an adjacency, OSPF database looks like:
>  <router># run show ospf database summary
>  Area 0.0.0.0:
>     2 Router LSAs
>  Externals:
>     3 Extern LSAs
>  Interface ge-0/1/0.22:
>
> When adjacency is up, it looks like:
>  <router># run show ospf database summary
>  Area 0.0.0.0:
>     2 Router LSAs
>  Externals:
>     14396 Extern LSAs  --> after a while, there appear all BGP routes
>  Interface ge-0/1/0.22:
>
> Now my questions:
> - Is that the default behaviour of a Juniper router ?
> - Why appear all BGP routes in OSPF database as external routes not before
> adjacency is up ?
> - How can i avoid appearence of these routes in OSPF database ?
> - How do i achieve that *only* default-route is announced to customer ?
>
>
> My corresponding OSPF specidic configuration looks as follows:
>
> routing-options {
>    static {
>        route 0.0.0.0/0 discard;
>    }
>    router-id <removed>;
> }
>
> policy-options {
>    policy-statement RM_DEFAULT_ROUTE_TO_OSPF {
>        term default-route {
>            from {
>                protocol static;
>                route-filter 0.0.0.0/0 exact;
>            }
>            then accept;
>        }
>        term explicit-deny {
>            then reject;
>        }
>    }
> }
>
> protocols {
>    ospf {
>        traceoptions {
>            file ospf size 500000 files 5;
>            flag state;
>        }
>        export RM_DEFAULT_ROUTE_TO_OSPF;
>        area 0.0.0.0 {
>            interface ge-0/1/0.22 {
>                authentication {
>                    simple-password <removed>;
>                }
>            }
>            interface all {
>                disable;
>            }
>        }
>    }
> }
>
> Thanks in advance for your help...
>
> Regards,
> Alex
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