%IP-3-LOOPPAK: Looping packet detected and dropped

Hoang Trong Nghia · ‎09-14-2015

Hi All,

I user my Core Switch(Cisco 3750) do DHCP server to Vlans. but Switch display messege :

01:07:32.110: %IP-3-LOOPPAK: Looping packet detected and dropped -
src=192.168.10.41, dst=192.168.10.254, hl=20, tl=78, prot=17, sport=137, dport=137
in=Vlan10, nexthop=192.168.10.254, out=Vlan10
options=none -Process= "IP Input", ipl= 0, pid= 199
-Traceback= 94F3CC 94F684 9516C4 9525DC 94FBF0 94FFB0 B61024 B611AC B3C9B4 970848 927BA0 93F3A0 93D2BC 93D518 93D794 1F13688
s

is this issue to effect to bandwidth of network ?

My config file at attach file

Pls help me !

Thanks so much

Peter Paluch · ‎09-14-2015

Hello,

I believe that the problem is caused by the improper use of the ip helper-address command in your configuration. Specifically, SVIs for VLANs 2, 3, 4, 5, 10, and 100 are configured with ip helper-address command that points to the address of the corresponding SVI interface:

interface Vlan2
 ip address 192.168.2.254 255.255.255.0
 ip helper-address 192.168.2.254
!
interface Vlan3
 ip address 192.168.3.254 255.255.255.0
 ip helper-address 192.168.3.254
!
interface Vlan4
 ip address 192.168.4.254 255.255.255.0
 ip helper-address 192.168.4.254
!
interface Vlan5
 ip address 192.168.5.254 255.255.255.0
 ip helper-address 192.168.5.254
!
interface Vlan10
 ip address 192.168.10.254 255.255.255.0
 ip helper-address 192.168.10.254
!
interface Vlan100
 ip address 192.168.100.254 255.255.255.0
 ip helper-address 192.168.100.254

Such a configuration makes no sense because it forces your switch to forward the received DHCP packet to itself. This is not necessary at all - your switch is directly connected to all networks for which it provides DHCP server functionality. You would be using ip helper-address only if the DHCP server was located on a different server.

Please remove all ip helper-address commands from your interfaces shown above, and verify whether the problem has been corrected.

Best regards,
Peter