Newbie routing question

[jameszapata62417]

Hi all 

Newbie here I am learning on my own. 

I have this topology :

I can ping from PC0 to G0/0 and G0/1 of Router0, but I can't ping G0/1 of Router1 . Router0 and Router1 can ping each other. 

I have done ip route 0.0.0.0 0.0.0.0 192.168.10.1 on Router0 but that doesn't do anything. I am not using any protocols, just static routing I'm after. Any suggestions or help greatly appreciated. 

[Nithin Eluvathingal]

you made default router on Router 0 pointing  to R1Gi0/1. but the R1 router doesn't know about the network 192.168.1.X. Thats the problem. 

add below static route on R1

ip route 192.168.1.0 255.255.255.0 192.168.10.2

[Martin L]

Using static routing means every router must have entry for every network it tries to reach. using default route helps reducing number of static routes.
Ping is 2-way process: you must know how to reach destination and back to the source (destination must know how to reach source).
you could do another default route on R1 or as suggested by N.E. above, add static route.
if this still does not work, you can attach your PT file here (must be a zip format)

Regards, ML
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[Georg Pauwen]

Hello,

just a quick remark: there has been another discussion here a few days ago, and @paul driver has made a very good point about two routers having default routes towards each other. I quote Paul:

--> Having default routes pointing directly to each other is asking for trouble, If this was on a production site it could cause a lot of issues basically what you are doing here is introducing a routing loop.

So default routes are better avoided...

https://community.cisco.com/t5/routing/how-to-make-vlans-talk-to-each-other-on-two-separate-network/m-p/4129163#M337703

[Richard Burts]

I agree that a default route on each router which points to the peer router is an invitation to problems. But I think that saying default routes should be avoided is an over reaction. A default route can be a very useful tool when we want to reach external destinations. But I do agree that we need to be careful when configuring more than one default route to make sure that the default routes are consistent with each other.

[Georg Pauwen]

I was assuming that it was understood that '"default routes are better avoided..." is only in reference to this specific scenario, where two routers point default routes towards each other...

I should have been more explicit. There are, obviously, millions of default routes on edge routers...

[Martin L]

as pointed out by others "another default route on R1" is not good idea (although it works), so I edited my previous post. Thanks.

[Joseph W. Doherty]

"Router0 and Router1 can ping each other."

Ah, but, by default, pinging from R0's g0/1 interface to R1's g0/1 interface. If R0 tries to ping PC1, or R1 tries to ping PC0 that should fail, along with R0 trying to ping R1's G0/0 IP or R1 trying to ping R0's G0/0 IP.

Routers "know" the networks of directly connect networks, but they somehow need to be "informed" of any networks not directly connected. The information is either the destination network, or a larger summary that contains the destination network and the "next hop" to send the packet to.

In your network, there are 3 networks, 192.168.1.0(/24?), 192.168.10.0(/24?) and 192.168.20.0(/24?).

R0 implicitly "knows" of 192.168.1.0(/24?) and 192.168.10.0(/24?).

R1 implicitly "knows" of 192.168.1.10(/24?) and 192.168.20.0(/24?).

Each router needs to be informed of the "far" network, 192.168.20.0(/24?) for R0 and 192.168.1.0(/24?) for R1. The information also includes "next hop".

If doing static routing, you would add, to R0:
ip route 192.168.20.0 255.255.255.0 192.168.10.1
and on R1:
ip route 192.168.1.0 255.255.255.0 192.168.10.2

but that's not the only way to do it. Since in larger networks, having every unique network can be difficult (imagine supporting the Internet's routes), there are ways to summarize blocks of networks. Using the "default route", one of those ways, is basically a wildcard that matches all unknown, networks.

So, although
If doing static routing, adding, to R0:
ip route 0.0.0.0 0.0.0.0 192.168.10.1
and on R1:
ip route 0.0.0.0 0.0.0.0 192.168.10.2

Would work, if PC0 tries to ping 192.168.2.1, when R1 gets the packet, from R0, it sends it back to R0, which sends it back to R1, which . . .

This would not happen with the first set of specific destination routes, I provided.

Generally, a default route is only used from the edge of a network directing packets toward the center of a network, not the converse.