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Community Member

ASA Firewall to Switch 3750 Basic configuration

Hi all
we are using asa firewall and other end is switch 3750 all the port are gigabit but in firewall all the port are ethernet. in ethernet:speed 100, duplex full..but in   switch end: auto is configured...we can configured like this;asa firewall e0/0 speed10, duplex full same as in the switch:g2/0/1:speed 10 duplex full. can we but it will work like half duplex..can any one assist me.     

Super Bronze

Hi, Is there any specific



Is there any specific reason why you are trying to set the speed/duplex manually?


Most of the time you should be fine setting both devices port to auto/auto setting. From what I have read on a quick glance setting the values manually/staticly on the device ports might cause problematic situation with some devices.


I usually tend to leave all settings auto, though there are situation where I have manually configured interface for 1000/full for example.


- Jouni

The way you have it

The way you have it configured you have a duplex mismatch.

100 Mbps, Full-duplexAUTO100 Mbps, Full-duplex100 Mbps, Half-duplex

Duplex Mismatch 1


As Jouni said make both sides Auto/Auto

or if you want make both sides 100/full

Cannot have one Auto and one 100/full.



Community Member

 Hi Jouni Forss/burleyman/All

 Hi Jouni Forss/burleyman/All,
Thanks for your answer.
But ok,come to your point only...when we leave both side auto, now it will working as a half duples--->right.
what will happend we configured like this...--->In switch-->Duplex full and in asa firewall--->Duplex full, We are not doing any thing about the speed... we will leave auto...what will be result....????wheather csma/cd will work or not.....?????
Thanks and Regards


Community Member

You can try this but if you

You can try this but if you dont see 3750 and ASA are talking to each other. then I would suggest to set 3750 speed as 100/duplex. followed by shut, no shut.

let us know what you see.

Community Member

Hi jigar Dave/All,one more

Hi jigar Dave/All,

one more thing, in switch 3750 all the port are gigabit-->speed 100/duplex..what about in ASA firewall--->all the interface are Ethernet-->can i configure speed 100/ will work or ......


Community Member

it should work.have you tried

it should work.

have you tried yet? because it looks like you are just asking questions, not replying what you have done and what's the result.

we are eager to know. please update us ASAP.

Community Member

Hi jigar/all,We will

Hi jigar/all,

We will implement on next week...sure  i will update to ....



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