Cannot ping switch

Unanswered Question
Aug 26th, 2009

So.. follow me here.


I'm on Host A which is connected to Router A. Router A connects to Router B which connects to Router C which connects to Switch A.


Pinging from Host A to Router C is successful, but pinging from Host A to Switch A is not possible.. and vice versa.. everything gets dropped at Router C.


Now, I've tried different MAC Addresses on the source NIC. I've cleared arp etc and I've checked the ACL on Router C and nothing. OSPF is running.


Any clue? My boss says I get a free day off if I figure this out. :)

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Lucien Avramov Wed, 08/26/2009 - 11:19

Turn on debug ip icmp on router C.

Go on router C and issue a ping with a source interface that connects t router B. Ping switch A. Does that work? I suspect it would, in that case it would mean most likely that Switch A does not have a default route or default gateway to router C and does not know about host A subnet. In that case, he is dropping the packet.


Turn on debug ip icmp on Switch A and see what happens on its console when you ping it from Host A. On switch A, you may need to add either a default route, default gateway or static route to the host A subnet via the interface that connects to Router C.


glen.grant Wed, 08/26/2009 - 11:31

As previous person said Switch a is missing a default static route if routing is turned on or if routing is turned off or it is a layer 2 switch only the default gateway is missing which would be the address of the subnet on the layer 3 routing device for mgt. address space. Post switch A config if possible. Check with the show ip route command on switch A or the show ip default command.

m-jankowski Wed, 08/26/2009 - 11:50

One detail... switch A is a Nortel switch.


Wouldn't all traffic traveling from Switch A be dropped then if it was missing a static route? All hosts on Switch A can communicate with Host A just the switch itself can't communicate with Host A and vice versa.

Richard Burts Wed, 08/26/2009 - 12:14

Michael


It would not impact traffic traveling through the switch. Traffic traveling through the switch is processed at layer 2, and there is no evidence in what you have posted that there is a layer 2 problem.


Access to the switch itself is handled at layer 3. And it appears to be at layer 3 where there is an issue. From the symptoms I would guess that one of these possibilities is the problem:

- is it possible that the switch is not configured with an IP address?

- is it possible that the switch is configured with an IP address, but that the IP address is not in the subnet that the router associates with the switch interface?

- is it possible that the switch has configuerd an IP address in its management VLAN but that the router to which it connects does not have a VLAN configured that corresponds to the management VLAN of the switch?

- is it possible that the switch does not have a default gateway configured? Or that the switch has a default gateway which is not the router interface address?


Your post does not tell us whether anything can ping the switch. It would be useful to know this. Can router C ping the switch? Can router B ping the switch?


HTH


Rick

m-jankowski Wed, 08/26/2009 - 12:44

Everything can ping the switch except for Host A. I've even changed the address on Host A and it starts working, its only the one IP address that isn't.


The default gateway is correct and the switch has an IP address in the correct subnet as the router.

Richard Burts Wed, 08/26/2009 - 12:57

Michael


That is helpful information. Could you provide the IP and mask of the switch and the IP and mask of host A?


I am wondering if it could be something like the address of host A could be valid or could be invalid depending on what you believe the mask is. Something like address 172.16.35.128 which is fine for a host if the mask is 24 but is invalid for a host if the mask is 25.


HTH


Rick

m-jankowski Wed, 08/26/2009 - 13:15

Host A is 10.180.1.218/16

Switch A is 10.186.40.100/16 I believe...


I don't think it's a mask issue though.

Richard Burts Wed, 08/26/2009 - 13:31

Michael


Is it possible that there is another device in the network that is also using address 10.180.1.218?

Is it possible that there is a static ARP entry that associates 10.180.1.218 with a different MAC address?


HTH


Rick

Lucien Avramov Wed, 08/26/2009 - 23:51

either provide us with the debugs or work on the nortel switch with the configuration of a static route for further help

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