As shown above, accessing internet through USG2100 is slow.
1. cpu-usage of USG2100 is 99%
2. There are warning messages in logbuffer as below:
%Mar 22 10:36:23 2013 USG2120BSR SEC/4/ATCKDF:AttackType:Udp flood attack; Receive Interface: Ethernet0/0/0 ; proto:UDP ; from 220.127.116.11:33634 18.104.22.168:52701 22.214.171.124:44838 126.96.36.199:54497 188.8.131.52:61329 184.108.40.206:2527 220.127.116.11:14622 18.104.22.168:40696 22.214.171.124:26268 126.96.36.199:44076 188.8.131.52:25043 184.108.40.206:40963 ; to 220.127.116.11:53 ; begin time :2013/03/22 10:35:55; end time: 2013/03/22 10:36:20; total packets: 199; max speed: 1014(packet/s);
1. Check the bandwidth and sessions on USG2100, and they are in normal range.
2. There are UDP attacks to 18.104.22.168, checking route to this ip address and found the nexthop is uplink device
<USG2120BSR>display fib 22.214.171.124
Route Entry Count: 1
Destination/Mask Nexthop Flag TimeStamp Interface TunnelID
0.0.0.0/0 126.96.36.199 GSU t Eth0/0/0 -
3. Checking the configuration on USG2100, found 188.8.131.52 which belongs vlanif 5 should connect to interface Ethernet1/0/4 whose current state is down.
ip address 184.108.40.206 255.255.255.248
port access vlan 5
Ethernet1/0/4 current state : DOWN
Line protocol current state : DOWN
4. The route on uplink device to 220.127.116.11 is USG2100, but USG2100 forwards the packets back to uplink router via default route because the interface which connect 18.104.22.168 is down. So, there is a route loop between USG2100 and uplink device.
5. This problem is resolved by configuring black hole route to 22.214.171.124 on USG2100
CPU usage too high usually caused by performance insufficient:
1. bandwidth/sessions/acl rules overload
2. route loop
4. ip duplicate
CPU usage abnormal usually caused by bandwidth/sessions/acl rules overload, route loop, attack, ip address duplicate and so on. When troubleshooting, please check them one by one.