Strange Ping Problem

I think it gets strange during the following;

Host A = 10.1.0.8/8
Host B = 10.10.10.1/24

Ok, I just tried that exact configuration with 2 machines on a switch without any default gateway configured. I started sniffers on both too.

When A pings B. Yes, A sends ARPs for B, B replys with it's MAC, A sends an ICMP request. But B DOES NOT reply with an ICMP reply. The ping times out.

When B pings A. Nothing is sniffed at all. The ping displays "Destination host unreachable".

I better try it with gateways too and see.

What OS's are you using ? I have definately seen this on early windows version so they may have changed it in newer ones ?

Both machines are WinXP Service Pack 2.

Sounds like they actually fixed something in XP then. Like Smurf I've seen this in the past too, I think it was under NT

Another situation that propagates this issue is when the router closest to host A (in ntwk 10.1.1.0/24) participates in a routing protocol (EIGRP for instance advertising 10.1.0.0/16) and the last hop router (10.1.2.129/25) before host B doesn't participate and was set up to route back to the previous hop network's addressing scheme (10.1.2.0/25 whose edge router 10.1.2.1/25 participates in the EIGRP process also but whose core switch does not.) only and therefore without a static will never know about 10.1.1.0/24 network.

I have seen this countless times whereby a site brings up a clinic, splits their IP scheme (in this example 10.1.2.0/24 into two /25s) with the clinic (PPP or otherwise attached to the site.)

Unidirectional routing occurs. (Said in the style of "The Dude abides.")

I have seen this countless times whereby a site brings up a clinic, splits their IP scheme (in this example 10.1.2.0/24 into two /25s) with the clinic (PPP or otherwise attached to the site.)

So at the end of the day, have you seen a host "A" pinging succussfuly host "B", but host "B" timeing out when pinging host "A" ? (without firewalls offcourse)