Networks

Ask something
Question Locked

Can't ping wireless to wireless

0 helpful
14 replies

by stein_brian

Closed to new repliesThis discussion is closed. It stays readable, but it takes no new replies.
Was hoping somebody could provide some insight for me on a weird behavior I am noticing. I am fairly to new to this environment and trying to troubleshoot a network I did not setup or have great knowledge of. What is happening is I can't seem to ping wireless machines from other wireless machines. However I can ping the wireless machines from a wired PC and vice versa. the wireless machines work fine, I just can't ping wireless to wireless. We have an ASA 5520 firewall and Cisco 4400 WLAN controller. I don't know if it's related to either of those or something totally different. Why would I be able to ping wireless-wired/wired-wireless, but not wireless-wireless? Thanks!

14 replies

by bfilmfan

I would suspect that ICMP ping is blocked at the firewall or switch to prevent network probing from a wireless bad guy.

by mddavis

Can the wired machine ping both of the wireless machines that can't ping each other? Or did you only test back and forth from one? Might be good to test ping to both of the wireless devices from the wired if you haven't already. Are the two wireless devices on the same WLAN (SSIDs) or different ones? If it isn't a ping blockage policy as the other person sugested and you can't ping both wireless devices from the wired PC then it may be a VLAN problem. If I remember correctly the Cisco wireless setup includes vlan tagging. If you allow ping (on the firewall) but don't have a layer 3 device between the two wireless devices then that may be your blockage.

by stein_brian

So quick question here - if there was some sort of ping blocking, would it be only on the firewall or could it be on the Cisco 3750 switches/routers? Or both? I would like to start there to see if there is a block in place, so what exactly would i be looking for? Would it be an ACL configured to deny ICMP traffic to the specific subnets/vlans which make up the wireless devices? Thanks!

by mddavis

Well the 3750 switch can have ACLs on it so it might be blocked there. I would look over the ACLs (if there are any configured) on the switch and see if there is anything allowing ICMP. You might want to test with pinging from the switch to and from each wireless device. Also try pinging between two wired devices that send traffic over that switch too. If you can ping from the switch to each wireless device but can't ping through the switch then it might be the switch blocking it. Are the two wireless devices on the same SSID or different ones. If I remember the Cisco controllers correctly they get all the fraffic sent back to them and then send it on. Do both of the access points use the same controller? Some more info on what's between the two devices might help here. :)

by robo_dev

some wireless adapters specifically block icmp.

by mddavis

I looked at the configuration guide for the controllers and I see the setting you're talking about...that may be what's causing your problem with pinging between two laptops on the same WLAN. Unfortunately I can't tell you if it will disprupt service to change this setting since I have never changed that setting. I will say that I have worked with the Cisco wireless systems and I doubt that it would cause a problem to change it but better safe than sorry. I would suggest that you wait and change the setting either before or after normal office hours (or maybe over lunch time) when a temporary glitch in the service wouldn't cause any problems.

by stein_brian

....and I will wait for a safe time to test this. Once I do test it I will post back my findings to let you know if it worked or not. Thanks so much!

by stein_brian

Well it's basically from what I can see a fairly simplified network. Meaning there are 5 locations, with everything ultimately flowing back to one main Data Center thru a Cisco 5507 switch/router and an ASA 5520 firewall. At each of the 5 locations they have a Cisco Catalyst 3750 switch, and from what I can see other than the IP Addresses assigned to each switch, they all have the same configuration with all the different VLANS. So that's really it between the wireless laptops, along with the WLAN controller. Yes they are on the same SSID. Here is an example - 2 wireless laptops sitting right next to each other - can log into both, browse the internet, network resources, etc, but can't ping each other. If i then patch one of the laptops in so it's wired, so now i have WLAN and LAN connected, and then turn off the wireless on that laptop, the other wireless laptop can now ping it. I can run a continuous ping and with the wireless off i can ping it fine, as soon as i enable the wireless i can't ping it, and then turn the wireless off and can ping again. I tried allowing incoming echo requests on the wireless card but still no luck.

by mddavis

Did you also allow echo replys on the wireless card? One thing you might try looking at is the windows firewall...I know that it allows you to add exceptions that are specific to the connection used so you might check to see if it allows ICMP on the LAN connection but not the wireless connection.

by mddavis

Also...the wireless controller can have ACLs configured on it. You might want to try checking the configuration on the controller and see if it has an allow statement for ICMP. The ACLs on the controller are just like any other...it has an implicit deny rule at the end so if there isn't an allow statement then it'll be blocked.

by stein_brian

OK so I apologize for the delay in posting here but I only just got a chance to get back to looking at this. So it seems after further investigation, I can't find and ICMP rules either in the firewall, the WLAN Controller, or in the Cisco Catalyst switches. However, it appears as if from a wireless laptop on one subnet, i can ping a wireless laptop on a different subnet, but I can't ping a wireless laptop on the same subnet. Does that make any sense to anyone? I would expect to see the opposite. It's almost as if when Wireless, something is seeing the ICMP request originating from the same segment and thus dropping it instead of forwarding it along. Has anybody seen something like this? I'm still doing more testing but this is what appears to be going on. Thanks!

by stein_brian

I found a setting in my Cisco WLAN controller called P2P Blocking which is currently set for Drop - Causes the Controller to discard the packets. Could this be the reason why I can't communicate between wireless machines on the same subnet? Is this safe to change and if so, can it be changed on the fly without affecting anyone who is currently connected wirelessly? Thanks!

by jool258963

Hello,
Have you solved the problem because I too have also the problem with Cisco 4400 series wireless controller
Thanks

This discussion is closed to new replies.