Ip helper address配置不当引起的故障

Ip helper address配置不当引起的故障

cisco3560上的配置：

interface Vlan1

description oss

ip address 132.99.19.158 255.255.255.224

!

interface Vlan2

ip address 132.99.20.38 255.255.255.224

ip helper-address 132.99.19.158

出现的告警：

1y8w: %IP-3-LOOPPAK: Looping packet detected and dropped -

src=132.99.20.34, dst=132.99.19.158, hl=20, tl=255, prot=17, sport=138, dport=138

in=Vlan1, nexthop=132.99.19.158, out=Vlan1

options=none

-Process= "IP Input", ipl= 0, pid= 142

-Traceback= 8A3600 99C400 99C6A4 99E0F4 99ED50 99CBC0 99CEE0 A8BBDC A8BD5C A692E8 9B7C20 97A20C 98EE2C 98D3B0 98D4D4 98D738

解决办法：

The recommended action is to analyze the source and destination address of the looped packets and verify that the configuration of the IP helper addresses in the router correctly points to the right device and does not point to the local router itself.

ip helper-address工作原理：

配置了helper-address的端口在接受到UDP(ip协议号17)数据包的广播时，删除广播的目的地址，并用特定的目的地址代替它，目的地址就是服务器地址。转发下列UDP端口的广播包：

TFTP 69

DNS 53

TIME 37

NETBIOS命名服务器 137

netbios数据报服务器 138

bootp服务器 67

bootp客户机 68

tacas 49