Hi Marty, You would think the router would use Net Unreachable if it had no route, rather than Host Unreachable. But I did some testing and got the same results as you. It sends Host Unreachable. I couldn't get it to send Net Unreachable, but I didn't do extensive testing. The RFC says that if the router determines it can't reach a host it can send Host Unreachable. I guess if it doesn't have a route, it's smart enough to know it can't reach the host. The RFC says this: "If, according to the information in the gateway's routing tables, the network specified in the internet destination field of a datagram is unreachable, for example, the distance to the network is infinity, the gateway may send a destination unreachable message to the internet source host of the datagram. In addition, in some networks, the gateway may be able to determine if the internet destination host is unreachable. Gateways in these networks may send destination unreachable messages to the source host when the destination host is unreachable." Thanks for the update. We now have one more piece to the puzzle. Priscilla At 05:29 PM 11/20/00, Marty Adkins wrote: >Priscilla Oppenheimer wrote: > > > > H means host unreachable. Jumping to the conclusion that there's a routing > > problem isn't logical (though I know that what's the Tech Note document > > says.) The host could be turned off. A host unreachable happens when the > > last-hop router tries to ARP for the device and doesn't get a response. > > >This isn't what I've seen and captured with a protocol analyzer, nor >viewed via debug. If any router is missing an ARP entry (or any other >type of next-hop data link address), it will silently drop the packet. >The output of "debug ip packet" will report "encapsulation failed". > >OTOH, if any router in the chain lacks a route to the destination, that >router will generate an ICMP _host_ unreachable, not network unreachable. >I agree this is not intuitive, but here's the screen output from a >WinThing attempting to ping a bogus address, and the debug output from >its default gateway: > >C:\WINDOWS>ping 10.0.0.1 > >Pinging 10.0.0.1 with 32 bytes of data: > >Reply from 192.1.63.196: Destination host unreachable. >Reply from 192.1.63.196: Destination host unreachable. >Reply from 192.1.63.196: Destination host unreachable. >Reply from 192.1.63.196: Destination host unreachable. > >Ping statistics for 10.0.0.1: > Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), >Approximate round trip times in milli-seconds: > Minimum = 0ms, Maximum = 0ms, Average = 0ms >-------------------------------------------------------------------------------------- >06:47:58: ICMP: dst (10.0.0.1) host unreachable sent to 192.1.63.198 >06:47:59: ICMP: dst (10.0.0.1) host unreachable sent to 192.1.63.198 >06:48:00: ICMP: dst (10.0.0.1) host unreachable sent to 192.1.63.198 >06:48:01: ICMP: dst (10.0.0.1) host unreachable sent to 192.1.63.198 > > Marty Adkins Email: [EMAIL PROTECTED] > Mentor Technologies Phone: 410-280-8840 x3006 > 275 West Street, Plaza 70 WWW: http://www.mentortech.com > Annapolis, MD 21401 Cisco CCIE #1289 ________________________ Priscilla Oppenheimer http://www.priscilla.com _________________________________ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
