Unable to ping some IP address within the same subnet

[Stephen Allen]

Greetings,

So I have two cisco 4331's that are connected via 4 PTP T1 connections. Router 1 can ping router 2. Router 1 can ping both hosts on router 2 network. Router 2 can ping some hosts on router 1's network, but not all of them.

I have the switch1 set with vlan 10 as 10.1.1.4, router 1 is interfaced with switch1 via G0/0/0 10.1.1.1. The switch is stacked, 48 port and 24 port.

Router 1 can ping all of switch1 hosts, but when I attempt to ping from router 2 to, lets say, host 10.1.1.56, it times out. I can't even connect to it (it's a camera in this case). However, if I ping from router 1 on 10.1.1.1 to 10.1.1.56, it resolves with no issues.

The really interesting thing is I have no issues pinging from router 2 to 10.1.1.80. Basically I can hit about 30% of the hosts from router 2, but 70% are unable to resolve any connection.

At first I thought it might be an issue with the stack, but some hosts on both switches can resolve a ping, while others can't.  If I ping with the source interface of s0/0/1 on router 1 to 10.1.1.56, it will not resolve, but if I ping with the same source interface to 10.1.1.80 it resolves with no issue.

I'm seriously scratching my head. Any help here would be fantastic.

[Richard Burts]

It would help us to give better answers if we had a better understanding of your environment. Perhaps starting with a simple diagram showing device connections and addressing.

But based with the little information that we have my best guess is that there is an issue with the configuration of some hosts (that are not pingable from the other router) and they do not have the correct default gateway (or perhaps not the correct subnet mask). Can you provide some details about this?

HTH

Rick

[Stephen Allen]

Rick,

I apologize for the lack of information. I recently got a new laptop at work and I don't have Visio installed yet.

Currently, these hosts that are being installed are configured by a contractor. They are suppose to handle everything past the router, and as the sysadmin, my job is just to make sure that we have connectivity between the routers until the contract is complete and I sign off on their work. I provided them with the correct subnet mask and gateway, but I wouldn't be surprised if they messed something up, this whole contract has been a mess from the start.

Today I'm going to go check the configurations of the hosts, hopefully that is the issue.

[Richard Burts]

When I first read the original post I was thinking that some hosts respond to ping and some hosts do not. That could be caused by home hosts having firewalls configured that do not allow incoming ping. But then I read the original post more carefully and notice that all hosts respond to ping from router 1. But from router 2 some hosts do not respond to ping. So that eliminates firewall issues as the cause of this problem. hosts that do respond to traffic from sources that are locally connected and do not respond to traffic from sources that are outside the local subnet are frequently caused by misconfiguration of the default gateway. And I guess that this is your issue. Please let us know the results when you have opportunity to check the gateway configured on those hosts.

HTH

Rick

[casanavep]

Just a question, have you tried to do the following afterhours (within an approved maintenance window): try to shutdown one path at a time and see if the loss goes away.  Without knowing more about the topology, we are simply left with guessing.  The fact that you have four parallel paths could mean that one of the paths has loss.  If a load balancing algorithm such as CEF is in use, traffic to one host from another may stay on one path, while another source-destination pair may ride another.  This could cause certain traffic pairs to show loss all the time due to how their load-balance places them and others to always be great.  There are many other factors such as routing, security policies, etc that could also be involved, but we probably need a better picture to figure out.