i want to check whether traffic for a particular port i,e, http(80),https(443),dns(53) is available on router or there is a problem from ISP end ? which command should i use and result would i be expecting.
1. Inside LAN switch / PC / FW to Router: Check with pings etc, and like leolaohoo above wrote, you can configure ACLs specifically permitting these ports with any any, to see if you get matches on the inside interface ACL.
2. Router itself: Check ACLs, PBR, QoS, and other interface / routing features.
3. Router to ISP: If the check in point 1. above passes, but your LAN users still can't get to the internet, check with a direct ping / trace from the router to say 22.214.171.124 or google etc.
If this fails, you need to ping your next-hop IP (default route gateway / ISP Router IP) and see if your last mile connectivity is fine.
If ping etc works fine, but you still can't access services, you should try a telnet to www.google.com on port 80 from the router.
This should atleast bring up a connection and when you type something you should see garbage. You can do the same with other TCP ports. For dns, the best way is to configure a dns server IP on your router, and try to ping a domain name, and see if the router can resolve it.
If the above are working fine, issue could be on the inside of the network.
Also, to ensure natting is fine, and if it's happening on the router, try sourcing your pings / traceroutes / telnets from the inside interface.
Lets say Fa0/0 is connected to Inside LAN switch, and Fa0/1 to ISP router:
@leolaohoo: acl is applied only on ip not protocols.....
@grenjen: thnx........ i think find the answer.....its telnet the 80 port.if no connection established then is it definitely not router issue but isp issue? i faced this kind of problem some days ago.it was later confirmed that isp has fault but i couldn't prove to client as solution provider representative.
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