From: Rob Laidlaw (laidlaw@consecro.com)
Date: Wed Mar 31 2004 - 23:33:49 GMT-3
This is covered in Halabi's "Internet Routing Architecture" somewhere in the
last few chapters. Basically what the route-map statement on the default
information-originate does is tell the router that it can inject a default
route into ospf as long as the route-map considitions are met. In this case
you want to make sure that the bgp route is from a particular neighbor so
what you'd do is this:
isp1 = 1.1.1.1
isp2 = 2.2.2.2
on the one router you'd have this:
access-list 10 permit 0.0.0.0
access-list 11 permit 1.1.1.1
route-map default permit 10
match ip add 10
match ip next-hop 11
route ospf 100
default information-originate route-map default
and on the other you'd have:
access-list 10 permit 0.0.0.0
access-list 11 permit 2.2.2.2
route-map default permit 10
match ip add 10
match ip next-hop 11
route ospf 100
default information-originate route-map default
This the two routers will only advertise a if the route map is true, which
means that you have a default route (access-list 10) and it is next-hop is
the ebgp neighbor (access-list 11).
Because this box is learning the default from the other ospf router, if it
were not for the route-map, it would continue to inject a default because it
would still have one even if the ebgp neighbor went down. Because the other
ospf default does not match the route map, router 1 will stop injecting the
default.
I would recommend checking out the halabi book for more info on this, it
under a section that deals with advertising defaults from mutliple ospf
routers.
Hope this helps.
-Rob
----- Original Message -----
From: "Scott, Tyson C" <tyson.scott@hp.com>
To: <ccielab@groupstudy.com>
Sent: Wednesday, March 31, 2004 4:26 PM
Subject: OT:Default-information originate in OSPF
> I have a question. I have been looking for a couple of hours to find a
> good explanation of the route-map option when originating a default
> route in OSPF
>
> http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft
> /122tcr/122tip2r/p2ftospf.htm#wp1025098
>
>
> This is the only link I can find. Or every link points back to this.
>
> What I am testing is options for using this besides calling from a route
> in the routing table. It says if you want to specify parameters besides
> the route in the routing table use the always keyword in addition to the
> route-map but it doesn't say after that what are the available
> parameters you can specify.
>
> Any one have any ideas?
>
> My idea was to stop advertising the default route if the eBGP peer
> relationship was down but I am unsure as to how to do this.
>
> For instance scenario as follows:
>
> ROUTER2 can still learn the external routes via ROUTER1 so it can still
> see the route in the routing table via iBGP. So if link to ROUTER4 goes
> down I want the default-information to stop being forwarded from ROUTER2
> into OSPF without the dependency on the route missing from the routing
> table. Or will setting the types of routes also work. IE:
>
> Route-map TEST permit 10
> Match route-type external
> Match ip address prefix-list TEST
>
> Ip prefix-list TEST permit 141.1.5.0/24
>
> ROUTER3 ROUTER4
> | |
> eBGP eBGP
> | |
> ROUTER1-------iBGP------ROUTER2
> | |
> OSPF OSPF
> INJECT DEFAULT INJECT DEFAULT
> | |
> ====================================
> | |
> | OSPF Area 0 |
> | |
> ====================================
>
> _______________________________________________________________________
> Please help support GroupStudy by purchasing your study materials from:
> http://shop.groupstudy.com
>
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Thu Apr 01 2004 - 08:15:50 GMT-3