Arp problem I think ...

Thu Dec 6 07:46:04 CST 2007

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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