IP default-route command query

what does this error message mean ?

Router(config)#ip route 0.0.0.0 0.0.0.0 g0/1
%Default route without gateway, if not a point-to-point interface, may impact performance

whereas why is the below command accepted ?

Router(config)#ip route 0.0.0.0 0.0.0.0 10.1.1.2

also what is the use of ip default-gateway command on a router
and is ip default-network part of ICND1 exam syllabus ?

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Comments

scratcherbob

If you use the no ip routing global configuration command to disable routing you would then need to add a default gateway to manage the router remotely. If you do turn routing off I think its a real kick in the balls for the router.

CiscoWayne

satishtech wrote: »

what does this error message mean ?

Router(config)#ip route 0.0.0.0 0.0.0.0 g0/1
%Default route without gateway, if not a point-to-point interface, may impact performance

whereas why is the below command accepted ?

Router(config)#ip route 0.0.0.0 0.0.0.0 10.1.1.2

also what is the use of ip default-gateway command on a router
and is ip default-network part of ICND1 exam syllabus ?

I'm pretty sure the command sending the traffic to the exit interface is still accepted, it's just telling you it'll have an affect on the performance of the router.

The best thing to do is to send it to the next hop IP address.

My understanding is, if you send it to the exit interface, the router will ARP for the final destination, rather than just the next hop. It just means the router will have to spend a lot more CPU power, processing the arp requests, vs the next hop IP address method.

pinkiaiii

ill try to give some input as recently went over that topic.

if you use show ip route command on router it will give you something like that.

Gateway of last resort is not set

192.168.0.0/24 is variably subnetted, 2 subnets, 2 masks

C 192.168.0.0/24 is directly connected, GigabitEthernet0/0
L 192.168.0.2/32 is directly connected, GigabitEthernet0/0

even thou i havent setup any static ip for next router or any routing protocols,the thing is once you set up static ip or rip,you will still get message that default gateway hasn't been setup,thus say you connect another pc and manage to input wrong default gateway address,that 0.0.0.0 0.0.0.0 s0/0/0 will point pc to right exit as its default one,instead getting cant reach host message.

Now i might be wrong since only been doning ccna for last month or so,and barely covered protocols as rip,so thats my understanding.
Also been tought to use rather exit interface like g0/1 or s0/0/0 instead next ip-not remember reason correctly thou why.

as for message above user might have given you answer if connection isnt to next router rather then one few more router in the way,the arp responses might put huge pressure on your router from other networks depending on size if say your exit leads to network with 100pcs etc.
none the less hopefully someone with more knowledge will answer properly as im interested in it myself to understanding it properly.

TWX

scratcherbob wrote: »

If you use the no ip routing global configuration command to disable routing you would then need to add a default gateway to manage the router remotely. If you do turn routing off I think its a real kick in the balls for the router.

Bear in mind that there's a difference between the global-configuration commands ip default-network and ip default-gateway. The former command works only if ip routing is enabled, and appears to do the same as entering a 0.0.0.0 route. I have to admit that I do not have enough practical experience that to know if there are any other differences between the two though.

I've found that the best way to remember ip default-gateway is that it's the command I use on L2 switches to provide a a means for my management IP address to communicate out of the subnet, so it does not apply to routers in the same way.

james43026

The simple fact is this, when you use a exit interface for a route, you are implying to the router that any network that matches your static route, are directly connected to that same interface, which means it will try to arp for any destination address that matches that static route and is going to traverse the exit interface specified. By default almost all routers should function just fine with this setup, minus the fact that CPU usage could skyrocket, because of all the ARP requests. This is because of proxy ARP, and any router that is connected to that exit interface, that knows how to reach that network, will respond to the ARP request with it's own interface MAC.

satishtech

thanks Scrathcerbob , but why would anyone disable routing on a Router ?

TWX

satishtech wrote: »

...why would anyone disable routing on a Router ?

Because it's going to be used in an IPv6 environment, or in an IPX/SPX environment, or some other non-IPv4 environment only?

Right now IPv4 is default, and IPv6 is disabled. One can enable IPv6 routing and dual-stack, or can go IPv6-clean and disable IPv4.