ASA is slowing down communication between Outlook and Exchange

Unanswered Question

Hi there,

I am having a strange issue with ASA 5520. It acts like a router between MPLS sites and a central site. Everything works good except for the Outlook -> Exchange traffic, users can see messages like: Outlook is trying to retrieve data from the Microsoft Exchange Server, and also that the network is too busy to send messages. When I plug the MPLS router directly to the core switch, it works great.


interface GigabitEthernet0/1.23

description core_switch

vlan 23

nameif inside

security-level 80

ip address


interface GigabitEthernet0/1.755

description MPLS Router

vlan 755

nameif mpls_vlan

security-level 80

ip address

I have enabled communication between interfaces with the same security level, and there is no access-list on both interfaces...


I have this problem too.
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pjhenriqs Tue, 01/29/2008 - 04:06


Have you checked the logging (ASDM or via CLI) to see if any traffic is getting blocked?


unviersityphysicians Wed, 08/13/2008 - 11:16

My company is experience a similar problem. Campus network with 100FX and 1000FX connections connect to an ASA 5520. Users experience delays between Outlook & Exchange. Logging did not show traffic being blocked. TAC suggested removing esmtp. no luck!

Can not find any good information on this issue.

We removed the ASA completly and the delays stop. Users are now routed directly into the core.

rkalia1 Sat, 01/17/2009 - 19:13

This is an MTU issue. Try setting the MTU size on appropriate interface.


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