Default Routing

datchcha

Ok, I am having a hard time grasping the concept of Default Routing.

Model:
Router1
E0:10.0.0.1
S0:10.0.1.1
Router2:
S0:10.0.1.2
E0:10.0.2.1
S1:10.0.3.1
Router3:
S0:10.0.3.2
S1:68.123.85.123 (ISP)

Question:
I place a default route on Router3 right? I am using static routes, but what i do not understand is – if i only place a default route on router 3, how does the local area network on Router1, E0 knows how to get to the Internet from Router3? I am super confused about this. Any help is greatly appreciated.

Netstudent

If you are using static routing, then you would have to go to each router and create a default route that points to Router3. Then on router3 you would need to create a default route to the internet. lets say a packet left Router1's E0 network destined for the internet. WHen the packet comes in router1, then it checks the routing table. It will see that it does not have an entry for the desintation network, and it will use the default route that you created to point to router3.

If you were using a routing protocol then you would add your subnets to the routing process, and then you would use the redistribute static command on router3 after you created the default route on router3. This would then send out a static route to the other routers saying "Hey if you get a packet that you don;t know about, send it to the edge router".

lex0429

anyone feel free to correct me...
A default route is used when a router doesnt have the destination network route in its routing table. It can only be used when there is only 1 exit point on the router.

Router A ----> Router B <

---

Router C

A, and B could have default routes but not B...Think along the lines of a default gateway...its that 1 exit point out of your network to the internet

datchcha

Netstudent wrote:

If you are using static routing, then you would have to go to each router and create a default route that points to Router3. Then on router3 you would need to create a default route to the internet. lets say a packet left Router1's E0 network destined for the internet. WHen the packet comes in router1, then it checks the routing table. It will see that it does not have an entry for the desintation network, and it will use the default route that you created to point to router3.

If you were using a routing protocol then you would add your subnets to the routing process, and then you would use the redistribute static command on router3 after you created the default route on router3. This would then send out a static route to the other routers saying "Hey if you get a packet that you don;t know about, send it to the edge router".

What should me default route look like on Router1?

I would use the ip default-gateway command right, since i am not using and routing protocols?

OK, so what you are saying is that i should create the following on Router1: ip router 0.0.0.0 0.0.0.0 10.0.1.2. Router2: ip router 0.0.0.0. 0.0.0.0 10.0.3.2. Router3: ip default-dateway or ip route 0.0.0.0 0.0.0.0 s1 (later will show AD as 0) is this all currect?

Oh and Congrads on the CCNA Netstudent. Hope to be with you soon.

Netstudent

yep that would work, but you will not use the ip default-gateway command. Basically you just created routes to send all unknown destination traffic to the internet.

the ip default-gateway command should only be used when ip routing is disabled on the router.

This article should clear up any confusion you have.
http://www.cisco.com/warp/public/105/default.html

earlier I said redistribute static which is for EIGRP, but or OSPF it would be default information orginate.


And thanks for the congrats!