Access Control Lists (ACLs) are a critical tool for identifying and managing network traffic. In this article, we will dive into the syntax for configuring numbered access lists on Cisco routers. Let’s get started!
Contents
Understanding Numbered ACL Syntax
To configure a numbered access list, there are two sets of syntax options available: one for standard access lists and one for extended access lists. These syntaxes allow you to configure either type of access list on a Cisco router.
Syntax for Numbered Access Lists
Here is the syntax for configuring a single line in a standard or extended access list:
access-list <id number> <action> <protocol> <source/destination>Let’s break down each part of this command to understand its purpose.
ID Number
Every access list entry is associated with an ID number, which links multiple entries together. This ID number also serves as a reference when applying the access list later in the configuration. In numbered access lists, the ID number must be a numerical value.
You can configure standard access lists by using ID numbers 1-99 and extended access lists by using ID numbers 100-199. Additionally, you can use ID numbers 1300-1999 to configure more standard access lists and ID numbers 2000-2699 for additional extended access lists.
Action
The action field specifies whether the access list entry permits, denies, or remarks on specific traffic.
- Use the “permit” action to accept traffic for a particular purpose.
- Use the “deny” action to reject traffic for a particular purpose.
- Use the “remark” action to add comments to the access list entry.
Protocol
The protocol field allows you to specify the type of protocol you want to match.
- Use “ip” to match all IP traffic.
- Use “tcp” or “udp” to match specific TCP or UDP protocols.
- Use “icmp” to match pings and trace route.
- There are various other protocols you can use, such as GRE or IPSec protocols.
Source/Destination
The source/destination field specifies the IP addresses and optional ports for either the source or destination of the access list entry.
- Use the network ID and wildcard mask to specify a single subnet.
- Use the “host” keyword followed by the IP address to specify a single IP address.
- Use the “any” keyword to specify all IP addresses.
In extended access lists, you can also specify ports using keywords like “eq” for equal, “range” for a range of ports, “gt” for greater than, “lt” for less than, or “neq” for not equal.
Conclusion
Configuring numbered access control lists may seem daunting at first, but understanding the syntax and purpose of each field makes it easier to manage network traffic effectively. Stay tuned for our next article, where we will configure access list entries together! For more information about Techal and its services, visit Techal.
FAQs
Q: How many access lists can I configure on a Cisco router?
A: You can configure up to 100 standard access lists and 100 extended access lists on a Cisco router.
Q: Can I use any ID number for a numbered access list?
A: No, the ID number determines whether it is a standard or extended access list. Use numbers 1-99 for standard access lists and 100-199 for extended access lists.
Q: Can I specify ports in a standard access list?
A: No, you can only specify ports in an extended access list.
Q: Is the port section optional in the access list syntax?
A: Yes, the port section is optional. If omitted, it matches on all ports.
Q: Can I add comments to access list entries?
A: Yes, you can use the “remark” action to add comments to access list entries.
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