Customers using a CISCO switch as the DHCP server, AR161F uplink sub-interface get address as DHCP client, customer found periodic oscillation on the up-lilnk sub-interface of AR161F. AR161F version is V200R005C30SPC200, the topology is as follow,
<EUR-AKL-RT1>display dhcp client interface GigabitEthernet 0/0/4.10
DHCP client lease information on interface GigabitEthernet0/0/4.10 :
Current machine state : Bound
Internet address assigned via : DHCP
Physical address : e036-765f-c0a6
IP address : 192.168.2.193
Subnet mask : 255.255.255.0
Gateway ip address : 192.168.2.254
DHCP server : 192.168.2.254
Lease obtained at : 2016-02-11 04:23:24
Lease expires at : 2016-02-11 04:28:24
Lease renews at : 2016-02-11 04:25:54
Lease rebinds at : 2016-02-11 04:27:43
DNS : 18.104.22.168
The analysis show oscillation period is the same as the DHCP debug period, so the period oscillation should related to DHCP renew.
Feb 15 2016 06:30:59+00:00 EUR-AKL-RT1 %%01IFNET/4/LINK_STATE(l):The line protocol IP on the interface GigabitEthernet0/0/4.10 has entered the UP state.
Feb 15 2016 06:36:05+00:00 EUR-AKL-RT1 %%01IFNET/4/LINK_STATE(l):The line protocol IP on the interface GigabitEthernet0/0/4.10 has entered the UP state.
Further analysis configuration, found that:
1. NAT was configured on the sub-interface with full UDP mapping,
nat server protocol udp global current-interface any inside 192.168.53.2 any
2. AR will send DHCP renewal messages on the half of lease time.
3.DHCP server-side reply the the DHCP renew packets will hit the NAT server, the original destination address 192.168.2.193 is replaced with 192.168.53.2.
Packets will be sent to 192.168.53.2 in stead of up-link, DHCP CLIENT unable to complete the renewal, till the lease time it will release the ip, and then retrieve the address, so the port will meet period oscillation.
Make the dhcp packets deny from NAT, without conversion. Here is the configuration:
[Huawei] acl 3100
[Huawei-acl-adv-3100] rule 5 deny udp destination-port eq bootpc
[Huawei] interface GigabitEthernet0 / 0 / 0.4
[Huawei-GigabitEthernet0 / 0 / 0.4] nat server protocol udp global current-interface any inside 192.168.1.20 any acl 3100
The above operation must clean up after the completion of NAT entries to take effect.
After configured above, we need reset the NAT table to make it work.
When configre NAT should pay attention to the DHCP packets, configure exceptions to avoid renewal packet loss cause interface oscillation