01-10-2011 10:39 AM - edited 03-06-2019 02:54 PM
Suppose you have these lines as part of a router's configuration:
no ip routing
no ip cef
interface FastEthernet0/0
ip address 192.168.0.1 255.255.255.0
no ip route-cache
duplex auto
speed auto
interface FastEthernet0/1
ip address 192.168.1.1 255.255.255.0
no ip route-cache
duplex auto
speed auto
ip default-gateway 10.0.0.1
When I have pinged 172.16.0.1 I have seen an ARP request with target address 10.0.0.1 sent out both the interfaces.
I have done this strange test because it was not clear which interface the router would have chosen in order to forward the packet.
Then I have thought that with the configuration ip default-gateway 192.168.0.2 the router would have chosen only interface fa0/0 in order to forward the packet. But instead the router have sent an ARP request with target address 192.168.0.2 out both the interfaces again.
This could make sense because without routing enabled all the interfaces are equivalent. So, is it correct to say that, without routing enabled, the router is like a "primitive" host with multiple interfaces? I have used the term "primitive" because normally a "non primitive" host does a minimal routing work instead.
Thanks.
01-10-2011 10:54 AM
Hi Speculor,
I am not able to understand the confusion!
The ip routing command is configured and that makes the device to work a layer 2.
The configuration and the description till test 1 makes perfect sense. Can you paste in the show run from the switch and give me a clear picture of the test conducted.
Questions to be answered:
1. Where did you initiated the ping from?
2. A show arp would aslo helpful
HTH
Rahul
01-10-2011 11:15 AM
Hello Rahul and thanks for your answer.
I am doing some tests with the GNS simulator and with a 7200 router.
I was pinging from the router itself and noting that, with the no ip routing command, those ARP requests are always sent
out both the interfaces, and it does not depends on ip addresses of interfaces and gateway.
You have said that the device works a layer 2: this is may be the best explanation and so the ARP broadcast are sent out all interfaces.
I was a little confused, may be for the presence of interfaces with ip addresses.
01-10-2011 11:24 AM
Hi Sepcilor,
When IP routing is disabled, the router will act as an IP end host for IP packets destined for or sourced by it, whether or not bridging is enabled for those IP packets not destined for the device. To re-enable IP routing, use the ip routing command.
Link for reference:
http://www.cisco.com/en/US/docs/ios/12_2/ip/configuration/guide/1cfipadr.html#wp1001889
HTH
Rahul
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