| Author |
Default routes question
|
|
| Boulware5 2004-01-12, 9:16 pm |
| Something I'm not totaly clear on. Let's say I have 3 routers, routerA, routerB, routerC. RouterC is a stub router which connects to the ISP. If you want to set up static routes for all, I know you also need to specify a default route. If the interface to routerC that goes to the internet is 192.168.1.1, do you have to *both* specify the default network *and* add the default route to routers A and B? The book we are using gives two examples, one using "ip route 0.0.0.0 0.0.0.0 192.168.1.1" and another using "ip default-network 192.168.1.1". So what I'm asking is if you have to specify both on routers A and B? | |
| DrWatsonJr 2004-01-12, 10:17 pm |
| Hey man,
It's to my understanding that both will accomplish the same thing. You use the ip default-network as a gateway of last resort when you have a routing protocol configured (otherwise you would use the ip default-gateway command). I would just use the "ip route 0.0.0.0 0.0.0.0 x.x.x.x" and you should be fine. | |
| Boulware5 2004-01-12, 10:21 pm |
| Yeah re-reading that section in the book, it seems like they are trying to say you can use either or. | |
|
|
| ZacDogg 2004-01-13, 1:00 am |
| ISP---C---B---A
If the above is what you are dealing with and I am following your question correctly, routerC will need a default route to the ISP, routerB will need a default route to routerC's interface that connects C & B and routerA will need a default route to routerB's interface that connects B & A.
You couldn't add a default-network on router's B & A to 192.168.1.0/24 because those routes aren't already existing in those router's to begin with. The "ip default-network" command flags an existing network as a default. Hope that made sense. The links that Darth added explain it pretty well.
Zac | |
| Boulware5 2004-01-13, 1:09 am |
| quote:
Originally posted by ZacDogg
ISP---C---B---A
routerB will need a default route to routerC's interface that connects C & B and routerA will need a default route to routerB's interface that connects B & A.
Why would router A need a default route to router B when we are assigning a static rout between A and B. Wouldn't router A need a default route to only router C since we already assigned a route from A to B? All packets not defined specifically by me will go to the specific interface for the default route (router C).
Now.. I may not make any sense. I have only taken my first cisco class last week. 
ADDED: By "default route" do you mean static route? If so, that makes a lot more sense to me. | |
| Demijohn 2004-01-13, 11:38 am |
| Router A doesn’t need a static route to reach B because A is directly connected to the B-A network. Router A will need a default route via B to reach C or the ISP.
Router B is directly connected to both the C-B and B-A networks so no routes are needed to reach those networks. A default route will be needed to get to the ISP and beyond.
Router C will need a default route via the ISP, and a static route to A.
Default routes are static routes, but static routes are not necessarily default routes. | |
| Boulware5 2004-01-13, 12:57 pm |
| quote:
Originally posted by Demijohn
Router A doesn’t need a static route to reach B because A is directly connected to the B-A network. Router A will need a default route via B to reach C or the ISP.
Router B is directly connected to both the C-B and B-A networks so no routes are needed to reach those networks. A default route will be needed to get to the ISP and beyond.
Router C will need a default route via the ISP, and a static route to A.
Default routes are static routes, but static routes are not necessarily default routes.
I see now what your saying. So routers directly connected to each other don't need static routes? | |
| Demijohn 2004-01-13, 2:56 pm |
| quote:
So routers directly connected to each other don't need static routes?
That is correct. | |
| ZacDogg 2004-01-13, 5:38 pm |
| quote:
I see now what your saying. So routers directly connected to each other don't need static routes?
They don't need static to reach only the other routers directly connected interface. To reach any other interface on that router and anything beyond it, it will need a route, be it static or dynamic.
quote:
Why would router A need a default route to router B when we are assigning a static route between A and B. Wouldn't router A need a default route to only router C since we already assigned a route from A to B?
The problem here is if you assign a default pointing to routerC, routerA doesn't know how to get to routerC. So, A needs a default/static to B, B needs a default/static to C and statics to any other networks than the directly connected on A, and C needs a default/static to the ISP and statics to A and any other networks on B.
quote:
Default routes are static routes, but static routes are not necessarily default routes.
Well said. | |
| dmaftei 2004-01-15, 9:08 am |
| quote:
Originally posted by Demijohn
Default routes are static routes...
I don't think that's true. If I remember correctly you can configure your routing protocols to generate and install default routes for you. | |
| Demijohn 2004-01-15, 12:11 pm |
| Your right. Folks might want to check this link as a starting point to a more detailed understanding of how this works. It's probably beyond CCNA level. |
|
|
|