Optimizing Cisco ASA Firewall Configuration

From my experience with Cisco ASAs over the last years it can make a big difference on the performance if the ASA is not correctly configured. You have to keep some things in mind when you install and set-up your firewalls. Of course for low traffic networks it will not make a big difference but for data centre infrastructures it can make a huge difference on the load of your CPU.

In the end from the network perspective everything can influence the performance: throughput (bit/s, packets/s and packet size), sessions (new and max connections), inspection and encryption (VPN). I recommend to have a look at the CiscoLive 365 presentation from 2012 – Maximizing Firewall Performance, very interesting presentation about the ASA hardware platform’s and what influence the performance.

At first some general information about the ASA platform’s before you start configuring

ASA5510 to 5550

  • On-board interfaces are better for higher packet rate


  • Traffic distribution over both I/O bridges
  • Keep flows on same I/O bridge and place interface pairs on the same card (inside and outside)


  • Possible to use jumbo frames but only make sense in end-to-end configuration

All ASA platform’s

  • Use port-channel for 1Gbit interfaces to split frames over┬ámultiple FIFO queues and RX rings (10Gbit interface have four RX rings)
  • Avoid inter-context traffic because it uses the loopback buffer

SNMP and Logging settings

Disable SNMP traps if not needed and use polling only

snmp-server host INSIDE poll community public version 2c

Only use one syslog server and proper trap level to reduce CPU overhead also adjust the ASDM logging

logging enable

logging host INSIDE
logging trap critical
logging history errors
logging queue 2048 

logging asdm warning 
logging asdm-buffer-size 512 

asdm history enable

Filter logging messages to reduce CPU overhead and prevent misconfigured debug logging to overload the CPU of the firewall

:: Build TCP Connection
no logging message 302013

:: Teardown TCP Connection
no logging message 302014

:: Deny udp reverse path check
no logging message 106021

:: Bad TCP hdr length
no logging message 500003

:: Denied ICMP type=0, no matching session
no logging message 313004

:: No matching connection for ICMP error message
no logging message 313005

:: Inbound TCP connection denied outside Firewall Access
no logging message 106001

:: Inbount UDP connection denied outside Firewall Access
no logging message 106006
no logging message 106007

Disable Threat Detection statistics

threat-detection basic-threat
no threat-detection statistics

Enable threat detection statistics only temporary because it can have a big impact on the performance of your ASA but keep basic threat detection always enabled!

ICMP interface settings

Not really related to optimizing the performance but ICMP should be correctly configured

icmp unreachable rate-limit 1 burst-size 1

icmp permit any echo OUTSIDE
icmp permit any echo-reply OUTSIDE
icmp permit any unreachable OUTSIDE

icmp permit any echo INSIDE
icmp permit any echo-reply INSIDE
icmp permit any unreachable INSIDE

Transport Protocol settings

Adjust default TCP MMS (Maximum Segment Size) 1380 to higher value (Please be careful sometimes it makes sense to leave it at 1380).

sysopt connection tcpmss 1460
sysopt connection tcpmss minimum 0

ASA silently drop packets without sending TCP reset.

no service resetinbound
no service resetoutside

Timeout value settings

Change timeout values for XLATE table, TCP/UDP sessions and Firewall Engine settings

timeout xlate 1:05:00
timeout udp 00:01:00
timeout conn 01:00:00
timeout half-closed 00:10:00
timeout h323 00:00:01
timeout sunrpc 00:01:00
timeout sip 00:05:00
timeout sip_media 00:01:00
timeout h225 00:00:01
timeout mgcp 00:00:01
timeout uauth 00:00:01 absolute

Antispoofing Options

ip verify reverse-path interface OUTSIDE
ip verify reverse-path interface INSIDE

Modular Policy Framework (MPF)

Modular Policy Framework provides a consistent and flexible way to configure security appliance features. For example, you can use Modular Policy Framework to create a timeout configuration that is specific to a particular TCP application, as opposed to one that applies to all TCP applications.
ACL and Class-Map for unrestricted IP traffic between backend networks

access-list UNRESTRICTED-IP-TRAFFIC extended permit ip object NET_10.1.100.0 object NET_10.2.100.0
access-list UNRESTRICTED-IP-TRAFFIC extended permit ip object NET_10.1.200.0 object NET_10.2.200.0
access-list UNRESTRICTED-IP-TRAFFIC extended permit ip object NET_10.1.300.0 object NET_10.2.300.0

class-map unrestricted-ip-traffic

ACL and Class-Map for any IP traffic

access-list ALL-IP-TRAFFIC extended permit ip any any

class-map all-ip-traffic
match access-list ALL-IP-TRAFFIC

Inspection Policy for DNS traffic

policy-map type inspect dns custom_dns_map
  message-length maximum 1280
  no nat-rewrite
  no id-randomization
  no tsig enforced
  no id-mismatch

Policy Map

Turn off not needed inspection to reduce processing overhead within the CPU. In the policy map you define the TCP connection quotas for the before configured class-map’s ACLs.

policy-map global_policy

  class inspection_default
   inspect icmp
   inspect icmp error
   inspect ftp
   inspect dns custom_dns_map

   no inspect rtsp
   no inspect pptp
   no inspect sip
   no inspect ctiqbe
   no inspect esmtp
   no inspect gtp
   no inspect h323
   no inspect h323 ras
   no inspect h323 h225
   no inspect http
   no inspect ils
   no inspect mgcp
   no inspect netbios
   no inspect rsh
   no inspect skinny
   no inspect snmp
   no inspect sqlnet
   no inspect sunrpc
   no inspect tftp
   no inspect xdmcp

  class unrestricted-ip-traffic
   set connection advanced-options tcp-state-bypass
   set connection per-client-max 0
   set connection conn-max 0
   set connection timeout embryonic 0:00:10
   set connection timeout half-closed 0:10:00
   set connection timeout tcp 1:00:00

  class all-ip-traffic
   set connection random-sequence-number enable
   set connection per-client-max 500
   set connection conn-max 0
   set connection embryonic-conn-max 100
   set connection per-client-embryonic-max 50
   set connection timeout embryonic 0:00:10
   set connection timeout half-closed 0:10:00
   set connection timeout tcp 1:00:00

Additional information

There are also some more points to think about what can influense the performance of the ASA firewall.

  • Several smaller ACLs are better than a large one (ACL size mostly impacts conn setup rate)
  • Static NAT entries are best for higher performance
  • Optimize dynamic routing because it has an impact on the CPU
  • Careful with inline packet capturing
  • Keep HTTP conn replication disabled for best performance results
  • Share the load with active virtual contexts on each firewall, see here my post: Cisco ASA Virtual Context Mode


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