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QoS using VPN ISM for ISR G2 routers


Does anyone have any experience or opnions about using QoS with the VPN ISM module on the ISR G2 routers?  The desire is to run a VPN tunnel from a remote site to a central site over the public Internet.  And before anyone chimes in I know there is no QoS over the INternet but I have found that if you run QoS at both ends and stay on the same providors network (All AT&T as an example) for all legs then you can achieve reasonable call quality most of the time.

Any advice, gotchas or differeing opinions are always welcome if done in the spirit of sharing.

Thanks in advance!

Super Bronze

QoS using VPN ISM for ISR G2 routers


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Hints include: shape for end-to-end bandwidth if less than physical bandwidth, avoid fragmentation (enable PMTUD across tunnel and use tcp mss adjust), if shaper doesn't account for L2 overhead - adjust rate to allow for it, if doing VoIP you may need to reduce shaper's Tc, you may want/need to decrease TX ring limit, don't share Internet link with non-VPN traffic or use multiple tunnels that might oversubscribe bandwidth.

I've found with above, quality usually good across Internet even with mixed carrries because usually only the Internet ingress and egress points congest.

New Member

QoS using VPN ISM for ISR G2 routers

Thanks for the info.  As a followup to you or anyone else who would care to chim in I would like to have 2 differnet ISP connections into a 1941 router with this module.  One would be the primary and the other would be the secondary.  Any input on how this module handles failover and failback?

Thanks in advance!

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