Weird Problem

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Jan 8th, 2010
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I have a 6500 switch connected to 4500 on a Layer II.  4500A acting as a layer III switch and is connected to other Core 4500B swith as a Layer III port.  The subnet between (2) 4500s are 172.24.200.56/30.


3750 config for Mgmt VLAN 182


int vlan 182

ip address 172.24.182.4 255.255.254.0

ip default-gateway 172.24.182.1


---------------------------------------------------------------


4500A

int vlan 182

ip address 172.24.182.1 255.255.254.0


I can't ping the interface 172.24.182.1 from 4500B switch, and

I think the reason is that the 6500 switch is acting as a Layer III switch, not layer II.

The "No IP Routing" wouldn't work on 6500 switch


6509(config)#no ip routing
% Incomplete command.



Any clue guys!

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sachinraja Fri, 01/08/2010 - 13:45
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Hi Abbas


why do the packets need to go to 6500.. you said you had a layer 3 interconnect between 4500 A and 4500 B.. In this case does the 4500 B know how to reach 172.24.182.1 ? show ip route 172.24.182.1 on 4500 B should point to 172.24.200.57 (4500 A interface) right ? Can you please clarify ?


Regards

Raj

Peter Paluch Fri, 01/08/2010 - 13:50
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Hello,


I do not think that the 6509 running the IP routing is the problem here. The configuration you have posted here seems to be correct. Can you go over the following suggestions?


  • You have created SVI interfaces for the management VLAN 182. However, have you created the VLAN 182 itself on all switches? Creating a SVI for a particular VLAN does not create that VLAN automatically.
  • Is the SVI interface Vlan182 up, line protocol up on all switches? Verify it using the show ip int brief command.
  • Are the interconnections between your switches correctly configured as trunks? Is the VLAN 182 allowed on them?


Regarding the command no ip routing on the 6509, the command line indicates you that this command is not complete. Use the question mark ? after the command to see which keywords must be used to complete that command.


Best regards,

Peter

Jon Marshall Fri, 01/08/2010 - 13:56
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I agree with Raj and Peter here, the 6500 should not be an issue.


If your 6500 is using a Sup720 you actually can't disable IP routing on the switch and even if the switch takes the command it will not be saved across a reboot. The command is there because it is part of IOS but is really only useful on routers.


If you don't create any L3 interfaces on your 6500 (other than maybe a management interface) then in effect your 6500 is acting as a L2 switch anyway.


Jon

abbas.ali Fri, 01/08/2010 - 14:45
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Folks,


I think the 6500 is an issue here.  I can ping 6500 svi interface 182 from a layer II switch, but not from any layer III switch since 6500 doesn't know how to route back to the originating subnet.  for example,


Initiating a ping from 4500 Switch B is on subnet 172.24.200.56, and 6500 doesn't know how to route back to this network.  The default-gateway command on 6500 wouldn't work, but it is acting as a layer III switch.  if we can't disable routing on 6500 then the only option for me to manage this switch remotely is to install a default route 0.0.0.0 0.0.0.0 unless there is any other way.


Thanks

Reza Sharifi Fri, 01/08/2010 - 20:04
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Hi Abbas,


If you are using the 6500 as a layer-2 switch, you only need a default gateway pointing to 172.24.182.1 (4500-A) just like the one you have on the 3750.

Is the managment 3750 switch physically connected to the 6500?

Did you create vlan 182 in all the devices and added it to the trunk?


HTH

Reza

abbas.ali Fri, 01/08/2010 - 23:22
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Hi Reza,


The IP default-Gateway command wouldn't work unless the Layer III routing is disabled, but can not be disabled due to sup720.  The IP Default-Gateway is configured on 6500, but the switch is not pingable outside of 172.24.192.0 network.

Giuseppe Larosa Sat, 01/09/2010 - 14:21
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Hello Ali,

about this aspect you have already found the solution:

if ip routing is enabled and it cannot be disabled you need to add a default route like

ip route 0.0.0.0 0.0.0.0 Next-hop-address


>> I can't ping the interface 172.24.182.1 from 4500B switch,


about your first issue you need to verify that the vlan 182 is present in all L2 trunks, that is that vlan182 topology is as expected.

If all devices are connected in the same broadcast domain the fact  that C6500 has or not has an ip address on this vlan is not important.

What counts is that ARP request reaches intended destination and answer goes back to requester.

If this works then IP connectivity should be fine.


Hope to help

Giuseppe

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