Cisco AnyConnect speed woes!

Darden, Patrick Patrick.Darden at
Tue Dec 9 20:02:57 UTC 2014

MTU should be automatically managed by the AnyConnect client.  With that said, have you done PMTUd (e.g. nmap --script path-mtu <dest-ip> from one endpoint to the next)?

I'd do a network map, working with your upstream provider, to identify and isolate variables.  E.g. to find media changes (wrt MTU changes/mismatches).
	--start with icmp traceroute
	--next do a udp traceroute
	--next do a tcp traceroute
	--each traceroute will give you a slightly different picture, some hops will respond to one but not another
	--try a vpn connection  from Upstream1 first, to see if it happens there.
	--try a vpn connection  from Upstream2 next, to see if it happens there.
	--try a vpn connection in reverse from Upstream2, then Upstream1, to see if the speed in one direction, via one or another portal, is faster.
	--continue to isolate networks, network devices, until you can find the point (e.g. advertisement injector) or process (e.g. MTU LCD or asymmetric routing) which is causing this.


-----Original Message-----
From: NANOG [mailto:nanog-bounces at] On Behalf Of Zachary McGibbon
Sent: Tuesday, December 09, 2014 1:42 PM
Subject: [EXTERNAL]Cisco AnyConnect speed woes!

I'm looking for some input on a situation that has been plaguing our new AnyConnect VPN setup.  Any input would be valuable, we are at a loss for what the problem is.

We recently upgraded our VPN from our old Cisco 3000 VPN concentrators running PPTP and we are now running a pair of Cisco 5545x ASAs in an HA active/standby pair.

The big issue we are having is that many of our users are complaining of low speed when connected to the VPN.  We have done tons of troubleshooting with Cisco TAC and we still haven't found the root of our problem.

Some tests we have done:

   - We have tested changing MTU values
   - We have tried all combinations of encryption methods (SSL, TLS, IPSec,
   L2TP) with similar results
   - We have switched our active/standby boxes
   - We have tested on our spare 5545x box
   - We connected our spare box directly to our ISP with another IP address
   - We have whitelisted our VPN IP on our shaper (Cisco SCE8000) and our
   IPS (HP Tipping Point)
   - We have bypassed our Shaper and our IPS
   - We made sure that traffic from the routers talking to our ASAs is
   synchronous, OSPF was configured to load balance but this has been changed
   by changing the costs on the links to the ASAs
   - We have verified with our two ISPs that they are not doing any kind of
   filtering or shaping
   - We have noticed that in some instances that if a user is on a low
   speed connection that their VPN speed gets cut by about 1/3.  This doesn't
   seem normal that the VPN would use this much overhead
   - We do not have the issue when connecting to VPN directly on our own
   network, only connections from the Internet

If you have any ideas on what we could try net, please let me know!

- Zachary

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