IP Route Command help

rford2798

Hi, I am working on some of my commands, getting ready for testing. One I am having some trouble with is IP route/ static routes. I thought I had a good understanding of it, but it seems like I cannot actually apply when I try to do it in Packet Tracer. The command is:

ip route (destination/remote network id and subnet)(local exiting interface or next hop ip).

I setup a Packet Tracer Lab like this:

PC1-S1-R1-R2-R3-S3-PC3

I have R1, R2 and R3 connected via serial. Connections on R1 and R2 are on s0/0/0 and on R2 to R3 on s0/0/1.

This is my addressing scheme:
R1 - s0/0/0 - 172.31.16.1/24
R1 - g0/1 - 192.168.1.1/24
R2 - s0/0/0 - 172.31.16.2/24
R2 - s0/0/1 - 172.30.17.1/24
R3 - s0/0/1 - 172.30.17.1/24
R3 - g0/1 - 192.168.2.1/24
PC1 - 192.168.1.2/24
PC3 - 192.168.2.2/24

If I want R1 to communicate with PC3, I would do:
ip route 192.168.2.0 255.255.255.0 172.31.16.2

When I do this in Packet Tracer, it is not working, I use a route on R3 pointing back to R1 as well:
ip route 192.168.1.0 255.255.255.0 172.30.17.1

Am I missing something or not understanding the command right?

Legacy User

Do you have a static route on R2 pointing to each side?

rford2798

I do not, would I need to configure a static route on each router both ways, I guess have routes on each device going to and from instead of just R1 and R3?

Priston

Without any static routes if you issue the show ip route command on R1
172.31.16.0/24, 192.168.1.0/24 are the only networks R1 knows about.

if you issue the show ip route command on R2
172.31.16.0/24, 172.30.17.0/24 are the only networks R2 knows about. (R2 doesn't know where either 192.168.x.x networks are)

if you issue the show ip route command on R3
172.30.17.0/24, 192.168.2.0/24 are the only networks R3 knows about.

Your telling R1 to go to R2 to get to the 192.168.2.0/24 network and R2 doesn't know where the 192.168.2.0/24 network is.

This is why we have routing protocols If you add more and more routers static routes would be a nightmare.

rford2798

Ok, that makes sense... I still have some work to do with studying...

Legacy User

Its cool dude, just keep studying and working on it, its a marathon not a race. Things will click over time.

james43026

Another helpful piece of advice(and I know you didn't do this in your example above). You shouldn't use an interface for a static route, as this causes the router to assume that the destination network is directly attached to the destination interface, and it will arp for every single destination address, thus possibly giving you an unnecessarily large ARP cache, introducing latency, and increasing CPU utilization. Both the latency and CPU utilization comes from the fact that a packet that needs an ARP request would be punted to the CPU for process switching / interrupt switching, instead of being processed by CEF, which is far slower, especially if we are talking a hardware based CEF router. The point is, be very careful with attaching interfaces to static routes.

toasterboy1

Might just be miss typed but do your R2 and R3 s0/0/1 interfaces really both have the same ip address: 172.30.17.1/24?