Arp problem I think ...

Thu Dec 6 15:42:02 CST 2007

In the end this was a mis configured switch.

Thank you all for your help.

Jason you had it correct.  I just need to slow down and think it though. 

Thank you all who had suggestions.

Alan

Desai, Jason wrote:
> Perhaps rather than arp specific issues, you are having more general
> broadcast issues?  I would suspect the switches - perhaps they are doing
> broadcast limiting or something like that.  Do thing work when
> connecting directly with a cross-over cable?
>
> Jase
>
>   
>> -----Original Message-----
>> From: linux-poweredge-bounces at dell.com 
>> [mailto:linux-poweredge-bounces at dell.com] On Behalf Of Alan Bunch
>> Sent: Wednesday, December 05, 2007 6:41 PM
>> To: linux-poweredge at dell.com
>> Subject: Arp problem I think ...
>>
>> Not stickily Dell related but the problem is on a Dell.
>>
>> Please bear with me as I know I have included a lot of detail.
>>
>> Description
>> Redhat AS 3
>> Kernel 2.4.21-47.0.1.ELsmp
>> eth0      HWaddr 00:07:E9:11:30:76
>>          inet addr:192.168.1.3  Bcast:192.168.1.255  
>> Mask:255.255.255.0
>>
>> eth0:1    HWaddr 00:07:E9:11:30:76
>>          inet addr:192.168.3.1  Bcast:192.168.3.255  
>> Mask:255.255.255.0
>>         This interface is up but with no IP address
>> eth1      HWaddr 00:07:E9:11:30:77
>>
>> eth1.101  10.10.1.1  Bcast:10.10.1.255  Mask:255.255.255.0  vlan 101
>> eth1.102  10.10.2.1  Bcast:10.10.2.255  Mask:255.255.255.0  vlan 102
>> eth1.103  10.10.3.1  Bcast:10.10.3.255  Mask:255.255.255.0  vlan 103
>> eth1.104  10.10.4.1  Bcast:10.10.4.255  Mask:255.255.255.0  vlan 104
>> eth1.105  10.10.5.1  Bcast:10.10.5.255  Mask:255.255.255.0  vlan 105
>> eth1.106  10.10.6.1  Bcast:10.10.6.255  Mask:255.255.255.0  vlan 106
>> eth1.107  10.10.7.1  Bcast:10.10.7.255  Mask:255.255.255.0  vlan 107
>> eth1.108  10.10.8.1  Bcast:10.10.8.255  Mask:255.255.255.0  vlan 108
>> eth1.109  10.10.9.1  Bcast:10.10.9.255  Mask:255.255.255.0  vlan 109
>> eth2      Link encap:Ethernet  HWaddr 00:06:5B:FE:56:C2
>>          BROADCAST MULTICAST  MTU:1500  Metric:1     eth3      Link 
>> encap:Ethernet  HWaddr 00:06:5B:FE:56:C3
>>          BROADCAST MULTICAST  MTU:1500  Metric:1
>>
>>
>> This machine is routing between the vlans.  When I ping 10.10.5.105 I 
>> get Host Unreachable.  Here is tcpdump from the ping on the router.
>>
>> tcpdump -i eth1.105
>> 14:10:28.254008 arp who-has 10.10.5.105 tell 10.10.5.1
>> 14:10:29.250067 arp who-has 10.10.5.105 tell 10.10.5.1
>> 14:10:30.250143 arp who-has 10.10.5.105 tell 10.10.5.1
>>
>> Ok now I go to the device via a serial port and ping back to 
>> 10.10.5.1 ( 
>> the router ) and here is the tcpdump output
>>
>> tcpdump -i eth1.105 -n
>> tcpdump: listening on eth1.105
>> 14:12:06.706722 arp who-has 10.10.5.1 tell 10.10.5.105
>> 14:12:06.706798 arp reply 10.10.5.1 is-at 0:7:e9:11:30:77
>> 14:12:06.707715 10.10.5.105 > 10.10.5.1: icmp: echo request (DF)
>> 14:12:06.707762 10.10.5.1 > 10.10.5.105: icmp: echo reply
>> 14:12:07.723100 10.10.5.105 > 10.10.5.1: icmp: echo request (DF)
>> 14:12:07.723136 10.10.5.1 > 10.10.5.105: icmp: echo reply
>>
>> Now of course I can ping 10.10.5.10 (the suspect device) from 
>> 10.10.5.1 
>> ( the router )
>>
>> ping 10.10.5.1
>> PING 10.10.5.1 (10.10.5.1) 56(84) bytes of data.
>> 64 bytes from 10.10.5.1: icmp_seq=0 ttl=64 time=0.068 ms
>> 64 bytes from 10.10.5.1: icmp_seq=1 ttl=64 time=0.039 ms       
>> This is fine untill the arp entry ages out.  Then I back to not being 
>> able to ping the device.
>>
>> When I add an arp entry manually all is well.
>>
>> No filters on the switches.  Switches are SMC 6826 and 8724s.
>>
>> I have several similar symptoms like this in various places.  I have 
>> some devices on vlans that I see the dhcp discover messages and I see 
>> the dhcp offer then the device sends another dhcp discover.  
>> This goes 
>> on for a few times and the device just waits and starts the 
>> process over.
>>
>> I feel that the problem lies in the handling of arp requests 
>> but I guess 
>> I just don't know enough about how linux handles them or how 
>> to control 
>> them to find a solution.
>>
>> I have lots of the devices on vlans that just work as you 
>> would expect.
>>
>> Any ideas ?
>>
>> Alan
>>
>>
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>>     
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