cebuano wrote: > > Just want to follow up on my first question. It turned out to > be a > misbehaving interface, i.e. Layer 1 issue. You do get a reply > with > a broadcast Ping from each host in the subnet. > However, in spite of the one router interface giving me issues, > I'm > Still trying to TRACE the logic as to how a second router can > elicit > a PING reply from the first router when Router1 cannot initiate > the > PING, in spite of the fact that both have each other's ARP > table > Aware of each other. If only the "debug ip icmp" would give you > an > Error output when the PINGs don't succeed.
The "debug ip packet" command might give you more useful data. It does output data even when the interface fails to actually send the packet. Also, put a protocol analyzer on the network. Analyzers make better troubleshooting tools than routers do. You said you can ping RtrA's e0 from RtrB, but can't ping RtrB's e0 from RtrA. This is indeed strange. Once you have fixed the physical-layer issues, check for access lists. That's one of the few things I can think of that would cause this problem. Also, check subnet masks. A router interface could receive a ping request and reply to it just fine, even its subnet mask is wrong. But it might fail to send a ping correctly if its subnet mask is wrong. Actual behavior when there are L1-L3 problems and misconfigurations can be pretty strange. It's often a waste of time to try to figure out the logic because the behavior may be inherently illogical under error conditions. Unless your job is to write the error-handling software routines, why ask why? Just fix the problem. That's the advice I have been giving to network admins for years and it has often helped them be more efficient. :-) Priscilla > Thanks. > Elmer > P.S. Kevin, I wish I had vocabulary like yours :-> > > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On > Behalf Of > Kevin Cullimore > Sent: Sunday, August 18, 2002 3:08 PM > To: [EMAIL PROTECTED] > Subject: Re: Simple (silly) question on PING [7:51580] > > ----- Original Message ----- > From: "cebuano" > To: > Sent: 17 August 2002 11:35 pm > Subject: Simple (silly) question on PING [7:51580] > > > > Hi all, > > Just two simple but annoying PING questions. > > 1. Why is it that on a broadcast medium, you can issue ping > > 224.0.0.5 and have all OSPF routers respond (according to > CCO), but > when > > I do a simple ping 192.168.10.255 on the subnet, no replies > are seen > > from all the interfaces on this subnet? I know you'll say my > brain is > > getting fried from too much "rack exposure". > > This is one of those cases that underscore the extent to which > communication > protocol specifications sometimes define a range of acceptable > behavior > in > the face of a given set of conditions rather than a single > acceptable > option. In some cases, the RFCs/Standards don't provide a > reccomendation > for > how a given implementation should behave, leading to real-world > interoperability issues. A more obvious case where these > considerations > matter involve the inexplicably persistent notion that distinct > implementations of a given standard should behave identically > given > identical circumstances. In this case, whether or not a given > icmp/ip > implementation responds to echo requests addressed to a layer 3 > broadcast > address is left up to the vendor (which used to provide a > quick-n-dirty > way > of performing simplistic os fingerprinting within a given > broadcast > domain), > based on the use of the may keyword when describing within RFC > 1122 when > describing the receiving host's behavior during that situation. > > The key here is that the guidelines covering behavior in > response to > received multicast & broadcast traffic are separate, allowing > for > distinct > behavior, which may, in turn, reflect different needs/goals to > be > addressed > when dealing with the two different (though conceptually > related) types > of > traffic. > > > > > > > 2. Using a crossover to connect two Ethernet interfaces, I > can ping > > say RtrA's e0 from RtrB, but can't ping RtrB's e0 from RtrA. > I know > some > > of you on the list have seen this before and have had a really > > crystal-clear explanation for this. > > > > TIA, > > Elmer > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=51657&t=51580 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
