Brocade Communications Systems 6650 manual Syntax show log, Syntax no ip access-group frag deny

Enabling strict control of ACL filtering of fragmented packets

Brocade# show log

Syslog logging: enabled (0 messages dropped, 2 flushes, 0 overruns) Buffer logging: level ACDMEINW, 9 messages logged

level code: A=alert C=critical D=debugging M=emergency E=error I=informational N=notification W=warning

Dynamic Log Buffer (50 lines):

0d00h12m18s:W:ACL: ACL: List 122 denied tcp 10.20.15.6(0)(Ethernet 4 0000.0004.01 10.20.18.6(0), 1 event(s)

0d00h12m18s:W:ACL: ACL: List 122 denied tcp 10.20.15.2(0)(Ethernet 4 0000.0004.01 10.20.18.2(0), 1 event(s)

0d00h12m18s:W:ACL: ACL: List 122 denied tcp 10.20.15.4(0)(Ethernet 4 0000.0004.01 10.20.18.4(0), 1 event(s)

0d00h12m18s:W:ACL: ACL: List 122 denied tcp 10.20.15.3(0)(Ethernet 4 0000.0004.01 10.20.18.3(0), 1 event(s)

0d00h12m18s:W:ACL: ACL: List 122 denied tcp 10.20.15.5(0)(Ethernet 4 0000.0004.01 10.20.18.5(0), 1 event(s)

0d00h12m18s:I:ACL: 122 applied to port 4 by from console session

0d00h10m12s:I:ACL: 122 removed from port 4 by from console session

0d00h09m56s:I:ACL: 122 removed from port 4 by from console session

0d00h09m38s:I:ACL: 122 removed from port 4 by from console session

Syntax: show log

Enabling strict control of ACL filtering of fragmented packets

The default processing of fragments by hardware-based ACLs is as follows:

•The first fragment of a packet is permitted or denied using the ACLs. The first fragment is handled the same way as non-fragmented packets, since the first fragment contains the Layer 4 source and destination application port numbers. The device uses the Layer 4 CAM entry if one is programmed, or applies the interface's ACL entries to the packet and permits or denies the packet according to the first matching ACL.

•For other fragments of the same packet, they are subject to a rule only if there is no Layer 4 information in the rule or in any preceding rules.

The fragments are forwarded even if the first fragment, which contains the Layer 4 information, was denied. Generally, denying the first fragment of a packet is sufficient, since a transaction cannot be completed without the entire packet.

For tighter control, you can configure the port to drop all packet fragments. To do so, enter commands such as the following.

Brocade(config)# interface ethernet 1/1/1

Brocade(config-if-e10000-1/1/1)# ip access-group frag deny

This option begins dropping all fragments received by the port as soon as you enter the command. This option is especially useful if the port is receiving an unusually high rate of fragments, which can indicate a hacker attack.

Syntax: [no] ip access-group frag deny

108	Brocade ICX 6650 Security Configuration Guide
	53-1002601-01