Wildcard Bits

How to Check the Corresponding Address Bits

–0 means check value of corresponding address bit.
–1 means ignore value of corresponding address bit.

Wildcard Bits to Match a Specific IP Host Address

–For example, 172.30.16.29 0.0.0.0 checks all the address bits.
–Abbreviate this wildcard mask using the IP address preceded by the keyword host (host 172.30.16.29).

Wildcard Bits to Match Any IP Address

–Accept any address: 0.0.0.0 255.255.255.255.
–Abbreviate the expression using the keyword any.

Wildcard Bits to Match IP Subnets

Access Lists

What Are Access Lists?
–Standard
- Checks source address
- Generally permits or denies entire protocol suite
–Extended
- Checks source and destination address
- Generally permits or denies specific protocols
• Inbound or outbound
Why Use Access Lists?
– Manage IP traffic as network access grows.
– Filter packets as they pass through the router
Access List Applications
– Permit or deny packets moving through the router.
– Permit or deny vty access to or from the router.
– Without access lists, all packets could be transmitted onto all parts of your network.
Other Access List Uses

- Special handling for traffic based on packet tests
Outbound Access Lists
• If no access list statement matches, then discard the packet.