Network Loop issues

oukpaka · ‎01-19-2008

The network consists of a 4507R Switch(Core) and 19 2960s as access switches.

Each on the Access swiches have vlan 1 and vlan x active on them. (where x is variable). Dhcp has been configured on the core for each vlan apart from vlan 1.

I noticed that each time a host is connected in any vlans i get a message in the core as follows:

src=10.1.2.155, dst=10.1.20.21, hl=20, tl=96, prot=17, sport=137, dport=137

in=Vlan1, nexthop=10.1.20.21, out=Vlan1

options=none

-Process= "IP Input", ipl= 0, pid= 82

-Traceback= 10A3B044 10A3B2E8 10A3CEFC 10A3DD04 10A3B854 10A3BBDC 10B96040 10B961C8 10B73C1C 10A57938 10A180F4 10A2DA14 10A2BBB8 10A2BD04 10A2BFC8 10623E5C

04:46:21: %IP-3-LOOPPAK: Looping packet detected and dropped -

src=10.1.2.155, dst=10.1.20.21, hl=20, tl=241, prot=17, sport=138, dport=138

in=Vlan1, nexthop=10.1.20.21, out=Vlan1

options=none

-Process= "IP Input", ipl= 0, pid= 82

-Traceback= 10A3B044 10A3B2E8 10A3CEFC 10A3DD04 10A3B854 10A3BBDC 10B96040 10B961C8 10B73C1C 10A57938 10A180F4 10A2DA14 10A2BBB8 10A2BD04 10A2BFC8 10623E5C

04:47:21: %IP-3-LOOPPAK: Looping packet detected and dropped -

src=10.1.2.155, dst=10.1.20.21, hl=20, tl=241, prot=17, sport=138, dport=138

in=Vlan1, nexthop=10.1.20.21, out=Vlan1

options=none

-Process= "IP Input", ipl= 0, pid= 82

-Traceback= 10A3B044 10A3B2E8 10A3CEFC 10A3DD04 10A3B854 10A3BBDC 10B96040 10B961C8 10B73C1C 10A57938 10A180F4 10A2DA14 10A2BBB8 10A

How do i resolve this. thanks

Edison Ortiz · ‎01-19-2008

Traceback messages aren't good to be seen on any Cisco device. What version of IOS this 4507 is running ?

Here is an explanation of the message:

IP-3-LOOPPAK : Looping packet detected and dropped -\nsrc=[IP_address], dst=[IP_address],

hl=[int], tl=[int], prot=[int], sport=[int], dport=[int]

in=[chars], nexthop=[IP_address], out=[chars]\noptions=[chars]

Explanation A looping packet has been detected. A very common cause is a

misconfiguration of an IP helper address. The helper address should be the same address as

that of the server of the intended service. Putting the address of the router in the

helper address causes a routing loop to be created.

Recommended Action Analyze the source and destination address of the looped packets and

verify that the configuration of IP helper addresses in the router is correctly pointing

to the right device and is not pointing to the router itself. "

In short, you shouldn't configure ip helper-address on the switch, if the switch is the DHCP server itself.

HTH,

__

Edison.

oukpaka · ‎01-19-2008

Thanks Edison,

Really appreciate, that was my error.