[AusNOG] Cisco GRE Tunnel weirdness

[Nathan Brookfield]

It sounds like an issue with a hop in the path.  Have you tried iperf or similar tests outside of the tunnel to both end points?

Kindest Regards,
Nathan Brookfield

Chief Executive Officer
Simtronic Technologies Pty Ltd

Web: http://simtronic.com.au
Phone: 1300 592 330
Fax: (02) 4749 4950

On 3 Jan 2014, at 17:49, "joe at apcs.com.au<mailto:joe at apcs.com.au>" <joe at apcs.com.au<mailto:joe at apcs.com.au>> wrote:

Hi List,

I have a GRE tunnel between 2 sites over a link limited to 1500 MTU.

As such we have mtu set to 1440 and mss-adjust to 1400 on both ends. This is overly cautious probably but it was working.

Anyway - it had been working quite fine for some time, but randomly we started seeing massive performance issues. Bandwidth throughput halved and ping times sky rocketed (~50ms to ~1000ms). We tried bringing down the tunnel and back up, no luck, and even power cycled each end (Cisco 3945's), no luck.

We have confirmed that the config's had not been changed for weeks. Neither end had crashed and rebooted. The tunnel itself did not go down between 'working' and 'not working'. Performance and ping times via the tunnel endpoint address' is fine, proving (to me) that the networks between the 2 sites are not the issue, but the tunnel itself. No links are saturated, and CPU performance is quite tame (both before and during the issue)

For now we have gone back to backup path but I haven't been able to find similar problems online, and my own Cisco tunnel experience leaves me empty so far.

Has anyone experienced a similar issue? A working tunnel suddenly having major performance issues?

Thanks,
Joe
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