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We are an ISP and I would like to implement ACL to protect our core network (Infrastructure) and implement some filtering on public subnet inside.

As border device we have a cisco WS-C4500X-32 4500x in VSS Cluster.

The peak traffic on downstream is 3Gbps. I follow the guidelines and I've already define the ACL, just left implement them.

My doubt now is how will be the throughput performance, if it's expected some degradation or the cpu will rise. Will the device can handle such traffic amount with filtering ?

I don't have the experience to implement ACL on so high throughput device.

[edit.1]

Sample of ACL :

ip access-list extended iACL 
 permit ip any 8.8.40.0 0.0.7.255
 permit ip any 8.8.48.0 0.0.15.255
 permit ip any 10.10.0.0 0.0.15.255
 permit ip any 9.9.248.0 0.0.3.255 
 ! External IP needing full access to our network
 permit ip 7.7.176.0 0.0.31.255 any 
 permit ip 6.6.32.0 0.0.31.255 any
 permit ip 5.5.160.0 0.0.31.255 any
 permit ip 4.4.128.0 0.0.31.255 any 
 deny ip any any

Device : cisco WS-C4500X-32 (MPC8572) processor (revision 4) with 4194304K/20480K bytes of memory. MPC8572 CPU at 1.5GHz, Cisco Catalyst 4500X

IOS : cat4500e-universalk9.SPA.03.04.00.SG.151-2.SG (ROM: 15.0(1r)SG6)

  • 1
    Could you share which specific IOS, supervisor and (hopefully) a sanitized example of the ACL? I assume there are no permit ... log entries, correct? – Mike Pennington Mar 28 '14 at 16:45
  • Added info. No 'permit .... log' entry for sure. Only subnet src/dst filtering, no layer 4 filtering. – cgasp Mar 28 '14 at 18:40
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The peak traffic on downstream is 3Gbps. I follow the guidelines and I've already define the ACL, just left implement them.

My doubt now is how will be the throughput performance, if it's expected some degradation or the cpu will rise. Will the device can handle such traffic amount with filtering ?

The 4500X uses a similar forwarding engine / TCAM to the Catalyst 4500 Supervisor7 (see Cisco Live 2013 BRKARC-3445 page 101 and afterwards for more info); this forwarding engine handles ACLs at 250Mpps as long as you don't punt packets to the CPU. Obviously permit or deny log entries will punt packets to the CPU for logging; however, long ACE port number expansions (such as permit tcp any any le 1024) also can force ACL CPU processing.

Based on your ACL example, you won't have a problem. You can apply these to your high capacity interfaces with no worries... I'm including an informational link to the official docs about How Catalyst4500 ACLs impact CPU

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