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Improve VPN tunnel performance


We have a customer with two sites using ASA 5505's to link them together.  They have a 60mb down, 12mb up connection with Comcast at both sites.  Their VPN tunnel maxes out around 500kbps.  I am looking for ways to try and improve the speed through the tunnel.  I am still fairly new at configuring ASA's and do not know exactly where to start trying to diagnose.  Any ideas would be greatly appreciated.

2 Replies 2

Dinesh Moudgil
Cisco Employee
Cisco Employee

You might want to tweak MSS/MTU size on the ASAs and clear df-bit on the outside interface of the ASAs as this will allow the packets to be fragmented rather dropped.

Here is a doc to get you started:

Start off with ping test, as defined in "VPN Encryption Error" section of this document.

Dinesh Moudgil

P.S. Please rate helpful posts.

Cisco Network Security Channel -

Hi xtech,

No issues we will be glad to assist you.

May I know if this issue is a new one or just started.

Sh cry isa sa det

Sh cry ipsec sa peer <remote peer <remote public IP> detail>

Sh asp drop //** with continuous traffic on collect this multiple time with interval of 5 seconds.

Collect simultaneous captures on both end inside for an application access which is experiencing slowness issue:

-set up capture on ASA:

Cap capin int <interface where inside server is reachable> match ip host <local inside host> host <remote host>

Cap drop type asp-drop all

Also you can check these documents for troubleshooting these issues:

PIX/ASA 7.x and IOS: VPN Fragmentation

Decrease the MSS to 1300 as discussed

sysopt connection tcpmss # - the default is 1380

In the ASDM

TCP Maximum Segment Size Overview

Don't Fragment through ASDM

Edit IPsec Pre-Fragmentation Policy

Configuration > VPN > IPsec > Pre-Fragmentation



Please rate helpful posts.

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