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How to fix bandwidth related issues and low throughput problem on ASA


Core issue

At times, the network faces a lot of latency due to the loss of bandwidth. Once traffic goes through ASA. 2.0 Mbps of link can drop down to 600-800 Kbps, and packets are dropped with many cyclic redundancy check (CRC) errors on physical interfaces.

There can be many reasons for this issue, however one of the common reasons is the speed and duplex set on physical interfaces.


In order to resolve this issue, set the speed and duplex on physical interface as AUTO. Refer to this configuration example in order to accomplish this task:

   asa(config)#interface ethernet 0/0

   asa(config-if)#duplex auto

   asa(config-if)#speed auto


   asa(config)#interface ethernet 0/1

   asa(config-if)#duplex auto

   asa(config-if)#speed auto

Note: If your network does not support auto detection, set the speed and duplex mode to a specific value.

Note: If you set the speed and duplex to anything other than auto on PoE ports, if available, then Cisco IP phones and Cisco wireless access points that do not support IEEE 802.3af are not detected and supplied with power.

If setting the speed and duplex to AUTO does not help, use the TAC Service Request Tool in order to contact Cisco Technical Support for futher assistance.