Whenever your testing if your connection is working (to be more specific if the traffic you are sending is really traversing the router/layer 3 switch) you can put an ACL on your router or layer 3 switch.

With this ACL you can specify the

  • source IP address
  • destination IP address
  • if known the source port with the protocoltype (not really needed)
  • the destination port with the protocoltype

With this access-list you can eather do a “debug ip packet access-list <access-list-name> detail” and see what is happening on the device in the logging.

Or you can just do a sh ip access-list <access-list-name> and check the hitcounts, correct?

WRONG!!!  This is a method that is working for a spcific range of Cisco routers and for all the Cisco firewalls (ASA/PIX/FWSM)

When you do a simple sh ip access-list <access-list-name>you will only see the counts for packets that are destined to the router but not the packets that are actually passing trough the device.

The ACL hitcounts is tracked by the hardware within the ASICs and can be checked with the following command:

show tcam interface <interface> acl  in ip

I’ve selected one of the 7600 routers that I manage to try this out

Output with the “sh ip access-lists TEST_ACL” command:

7600-router#sh ip access-lists TEST_ACL
Extended IP access list TEST_ACL
    10 permit ip any xx.xx.xx.xx 0.0.0.63
    20 permit ip any xx.xx.xx.xx 0.0.0.255
    30 permit ip any xx.xx.xx.xx 0.0.0.255
    40 permit ip any xx.xx.xx.xx 0.0.0.15
    50 permit ip any xx.xx.xx.xx 0.0.0.31
    60 permit tcp host xx.xx.xx.xx host xx.xx.xx.xx eq bgp (28341 matches)
    70 permit tcp host xx.xx.xx.xx host xx.xx.xx.xx eq bgp
    80 permit icmp xx.xx.xx.xx 0.0.0.3 xx.xx.xx.xx 0.0.0.3
    90 permit icmp xx.xx.xx.xx 0.0.0.3 xx.xx.xx.xx 0.0.0.3
    100 permit icmp xx.xx.xx.xx 0.0.0.255 host xx.xx.xx.xx
    110 permit icmp xx.xx.xx.xx 0.0.1.255 host xx.xx.xx.xx
    120 permit icmp xx.xx.xx.xx 0.0.0.255 host xx.xx.xx.xx
    130 permit icmp xx.xx.xx.xx 0.0.1.255 host xx.xx.xx.xx
    140 deny ip any any (8 matches)

Output with the “sh tcam int X acl in ip” command:

7600-router#show tcam interface gigabitEthernet 1/0/1.100 acl  in ip   
Global Defaults shared
Entries from Bank 0
Entries from Bank 1
    permit       ip any xx.xx.xx.xx 0.0.0.255 (314 matches)
    permit       ip any xx.xx.xx.xx 0.0.0.255 (1316 matches)
    permit       ip any xx.xx.xx.xx 0.0.0.63 (68 matches)
    permit       ip any xx.xx.xx.xx 0.0.0.31 (389 matches)
    permit       ip any xx.xx.xx.xx 0.0.0.15 (2 matches)
    permit       icmp xx.xx.xx.xx 0.0.0.3 xx.xx.xx.xx 0.0.0.3
    permit       icmp xx.xx.xx.xx 0.0.0.3 xx.xx.xx.xx 0.0.0.3
    permit       icmp xx.xx.xx.xx 0.0.1.255 host xx.xx.xx.xx
    permit       icmp xx.xx.xx.xx 0.0.1.255 host xx.xx.xx.xx
    permit       icmp xx.xx.xx.xx 0.0.0.255 host xx.xx.xx.xx
    permit       icmp xx.xx.xx.xx 0.0.0.255 host xx.xx.xx.xx
    permit       tcp host xx.xx.xx.xx host xx.xx.xx.xx fragments
    permit       tcp host xx.xx.xx.xx host xx.xx.xx.xx fragments
    permit       tcp host xx.xx.xx.xx host xx.xx.xx.xx eq bgp (14350 matches)
    permit       tcp host xx.xx.xx.xx host xx.xx.xx.xx eq bgp