[AusNOG] Cisco GRE Tunnel weirdness

[Nathan Brookfield]

It doesn't sound like an MTU issue to me that's for sure.... Hmmm!

Kindest Regards,
Nathan Brookfield (VK2NAB)

Chief Executive Officer
Simtronic Technologies Pty Ltd

Local: (02) 4749 4949 | Fax: (02) 4749 4950 | Direct: (02) 4749 4951
Web: http://www.simtronic.com.au | E-mail: nathan.brookfield at simtronic.com.au




-----Original Message-----
From: joe at apcs.com.au [mailto:joe at apcs.com.au] 
Sent: Friday, 3 January 2014 6:06 PM
To: Nathan Brookfield
Cc: ausnog at lists.ausnog.net
Subject: Re: [AusNOG] Cisco GRE Tunnel weirdness

Not specifically iperf but I was able to send 1500byte ping request with df bit set, outside of the tunnel, with no issues. (1501 bytes failed)

This indicated to me that the path between the 2 sites should be OK. Let me know if you disagree?

On 2014-01-03 17:51, Nathan Brookfield wrote:
> 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 [1]
> Phone: 1300 592 330
> Fax: (02) 4749 4950
> 
>  On 3 Jan 2014, at 17:49, "joe at apcs.com.au" <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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