When troubleshooting a problem with Access Control lists, one of the things you would want to do is to clear the counters on the ACL matches.
In Cisco IOS, you can clear the ACL Matches counters as follows:
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Another beginner tip that can be useful!
When you work on the Cisco Router or Catalyst Switch console, it would be annoying to have the console or terminal (telnet/ssh) logs to pop in between your commands. This can be even more irritating when it is busy switch or a router spitting messages continuously.
With Cisco IOS version 11.2, Cisco introduced the Named ACLs. Named ACLs are Standard or Extended ACLs which are give names instead of a ACL number. Technically, other than giving a name to the ACL there isn't any other difference when it comes to the functionality as in Standard or Extended ACL.
Extended ACLs are advanced than the Standard ACLs. Unlike the Standard Access Lists where it checks only the Source IP Address to control the flow of the packets, Extended ACLs can check the
Source & Destination Address
Protocols (IP,ICMP,TCP,UDP)
Source & Destination ports
While we saw here how to setup a Cisco Router as a Caching/Forwarding DNS Server. We can now look at how to make your Cisco Router as an Authoritative DNS server. When configured as an authoritative name server for its own local host table, the router listens on port 53 for DNS queries and then answers DNS queries using the permanent and cached entries in its own host table.
Careful consideration has to be given as this can consume considerable amount of resources like CPU cycles on the Cisco Router. If you are a small network and realise your Cisco ROuter is under utilised then there is a good business case to turn your router into a DNS server.
A Cisco Router running Cisco IOS can function as a Caching or Forwarding DNS Server which answers to DNS queries from clients either from its host table or cache or forward it to a DNS server which can respond to the query.
This feature can come in handy in small network environments where the router can act as a Caching DNS server forwarding queries to the ISPs DNS servers or infact any external DNS servers. Also, makes sense using on under utilized DNS servers.
Cisco IOS supports multiple IP Addresses on an interface. There will be one Primary IP Address on the interaface and multiple Secondary IP Addresses on the interface. There is no limit on the number of IP Addresses that can be configure on an interface. Configurng multiple IP Addresses on your cisco routers can sometime help where you have multiple subnets having one physical router interface.
The IP Addresses can be from different subnets and from different networks.
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