I am simulating a simple network technology with IOU L3 images and observe a strange behavior with image version 17.15.1
The network consists of 4 routers,
One of them is named a "SourcePC" (bottom of diagram) - a router from which I do an ICMP ping (ping command)
I am pinging a "loopback 0" (192.168.4.1) interface on another router (right top side of diagram) which is behind an intermediate router (in the middle of diagram)
The "SourcePC" router has the following configuration:
configure terminal
interface ethernet 0/1
ip address 192.168.2.2 255.255.255.0
no ip proxy-arp
no shutdown
exit
ip route 0.0.0.0 0.0.0.0 192.168.2.1
In fact in target configuration there will be "no ip proxy-arp" configuration on any interface involved in this scenario
What I observe with 17.15.1 is that the "SourcePC" is making an ARP request for 192.168.4.1
This is completely different to image 15.4 -the "ping 192.168.4.1" results in "SourcePC" asking arp request of 192.168.2.1 - which is completely correct
It looks like the "no ip proxy-arp" controls only whether the router responds to an ARP request for IP from different network - but doesn't control whether the router sends such ARP request.
My questions ... is there any setting that controls that ? - How can I prevent Cisco router for doing such bizzare / incorrect thing ?
Hi everyone !!
Thank you kindly for your response and the will to help
@bb - Balaji, I think my case is diffrent. I was looking at these pages sent by you and the describe a case when the host is "incorrectly" configured with "different" mask (shorter mask, including two or more subnets). In my case I use mask /24 everywhere.
@dan - I heard about this case, but looking at "ip route" it shows that the only static route is a default route and it poings to a next hop IP.
The second image shows that there is an arp entry which was filled by a response from intermediate route - but this is because I have re-enabled "proxy arp" on intermediate router. If I disable it - there will be no ARP response and no ARP entry on "SourcePC"
Is there a chance that the real (no IOU) image works differently ? ... as I have said - the image 15.4 has a different behavior - it uses the default gateway for ICMP ping.
@MHM - how to check if the NAT is enabled ?
@Harold - I have a strange feeling the issue is very like to "ip cef" settings
Exactly the "ip cef" subject is quite unclear yet for me - I am trying to learn a little about Cisco CCNP routing subjects, but in fact my knowledge is very poor - I have not worked with Cisco routers since 2011.
