Troubleshooting

Unusual Network Activity

Error (Invalid input) when entering an IP address.

When using the “host” option in the command syntax, ensure that you are not including a mask in either dotted decimal or CIDR format. Using the “host” option implies a specific host device and therefore does not permit any mask entry.

Correct.

Incorrect. No mask needed to specify a single host.

Figure C-2. Examples of Correctly and Incorrectly Specifying a Single HostApparent failure to log all “Deny” Matches.

Where the log statement is included in multiple ACEs configured with a “deny” option, a large volume of “deny” matches generating logging messages in a short period of time can impact switch performance. If it appears that the switch is not consistently logging all “deny” matches, try reducing the number of logging actions by removing the log statement from some ACEs configured with the “deny” action.

The switch does not allow any routed access from a specific host, group of hosts, or subnet.

The implicit deny any function that the switch automatically applies as the last entry in any ACL may be blocking all access by devices not specifically permitted by an entry in an ACL affecting those sources. If you are using the ACL to block specific hosts, a group of hosts, or a subnet, but want to allow any access not specifically permitted, insert permit any as the last explicit entry in the ACL.

The switch is not performing routing functions on a VLANTwo possible causes of this problem are:

Routing is not enabled. If enabled, use the ip routing

show running indicates that routing is not command to enable routing.

On a switch covered in this guide, an ACL may be blocking access to the VLAN. Ensure that the switch’s IP address on the VLAN is not blocked by one of the ACE entries in an ACL applied to that VLAN. A

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