Intermittent ping failures between vlans

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Apr 6th, 2009
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running a 4006 with 5 actively used vlans, IOS 12.1(8a)EW1

vlans 104 and 105 used for workstations, vlans 103 and 115 used for servers.

vlan 106 used for RAS. DHCP on vlans 104, 105 and 106 only.

hosts on vlan 104 having intermittent problems (ping = request timed out) accessing a single host on vlan 115, but can access other hosts on vlan 115 no problem

when the 'problem' host on 115 is unreachable from 104, it can still be pinged ok from another host on vlan 115.

anyone seen this before?

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rblankers Mon, 04/06/2009 - 11:21
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just to be clear, the hosts in the same (115) vlan never lose connectivity, but connectivity from all other vlans (103,104,105,106) is intermittent...

Istvan_Rabai Mon, 04/06/2009 - 11:23
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Hi Robert,

Based on your description I would check the following:

1. On the 'problem' host, the ip addressing and mask is correct for VLAN115.

2. If ip proxy-arp is disabled on the 4006.

3. If any access-lists on the vlan interfaces are preventing the connection.



lamav Mon, 04/06/2009 - 11:29
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Post the config, if you can.


rblankers Mon, 04/06/2009 - 11:55
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here is my config

the 'problem host' is currently on port fa3/40. I had switched it to port fa3/42 but switched back after this did not correct the issue.

at this moment, I can ping from another host on 115 but not from a host on 104.

thanks all

rblankers Mon, 04/06/2009 - 11:35
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1. verified ip and mask are correct

2. please explain - should it be enabled or disabled?

3. don't believe this could be a problem as connection is intermittent, can't be narrowed down based on day/time

glen.grant Mon, 04/06/2009 - 14:48
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This smacks of an old problem on catos boxes which did basically the same thing, though those were layer 2 only. That is really old code , I bet if you upgrade the code and reload your problem will go away.

rblankers Tue, 04/07/2009 - 06:48
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thanks - will try to upgrade this weekend if still not resolved. I am replacing this switch in 2 months since it's EOL/EOS anyway...

the 'problem host' is an Avaya audix voicemail server, and after discussing with peers have learned that they have seen flaky issues of this sort related to the ip stack on the server, so it may not be a problem with the switch after all. I'll update once I find a resolution, appreciate the suggestions from everyone.

glen.grant Tue, 04/07/2009 - 09:43
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Oh avaya , should have said something. A lot of their voip gear is weird , we have seen where they will reply to every other ping packet. It is an avaya issue. If it pings ok on the same vlan but not from another of course check the default gateway of the device.

rblankers Tue, 04/07/2009 - 09:46
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the server in question is an audix (voicemail) server, not voip, but I heard from a colleague that he had seen an issue where the audix server 'forgot' what the default gateway is, even though looking at the config it is clearly set correctly. this would explain the problem with inter-vlan routing while intra-vlan routing continues to operate.


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