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 126.96.36.199:33634 188.8.131.52:52701 184.108.40.206:44838 220.127.116.11:54497 18.104.22.168:61329 22.214.171.124:2527 126.96.36.199:14622 188.8.131.52:40696 184.108.40.206:26268 220.127.116.11:44076 18.104.22.168:25043 22.214.171.124:40963 ; to 126.96.36.199:53 ; 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 188.8.131.52, checking route to this ip address and found the nexthop is uplink device
<USG2120BSR>display fib 184.108.40.206
Route Entry Count: 1
Destination/Mask Nexthop Flag TimeStamp Interface TunnelID
0.0.0.0/0 220.127.116.11 GSU t Eth0/0/0 -
3. Checking the configuration on USG2100, found 18.104.22.168 which belongs vlanif 5 should connect to interface Ethernet1/0/4 whose current state is down.
ip address 22.214.171.124 255.255.255.248
port access vlan 5
Ethernet1/0/4 current state : DOWN
Line protocol current state : DOWN
4. The route on uplink device to 126.96.36.199 is USG2100, but USG2100 forwards the packets back to uplink router via default route because the interface which connect 188.8.131.52 is down. So, there is a route loop between USG2100 and uplink device.
5. This problem is resolved by configuring black hole route to 184.108.40.206 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.