<html><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12pt"><div>Seemingly unrelated, but today two separate customer issues that have come to me:</div>
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A 2M p2p Telstra service where usable MTU across the link has dropped
overnight to approx 200 bytes in size (from 1500). This caused OSPF to drop on the link and forced traffic onto a 3G backup service (fault logged with carrier)<br></div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><br></div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;">2. Another customer reported that GRE has stopped working to their firewall that we provide IP connectivitiy to. Nothing changed by us, nothing changed by them, they are scheduling a reboot of the firewall.</div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><br></div><div
style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;">To top it off I've been having wierd issues on my link at home for the last couple of days (resold Telstra DSL port) and have just checked and for some reason the MTU on the virtual-access interface on our LNS for my service is not 1460 instead of the 1500 that it was previously. Setting "adjust-mss" on the LAN of my router has resolved my inability to access web stuff that was timing out, but leaves me no closer to knowing WHY the MTU has suddenly changed.<br>
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<div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><br></div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><br></div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;">Coincidence or conspiracy, who knows....</div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><br></div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;
background-color: transparent; font-style: normal;"><br></div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;">As someone else said, try monitoring CPU & interface utilisation (graph via SNMP) to see whether that is taking a hit during your times of slowness. Is this a GRE tunnel over Internet or something else ? What speed ? 3945's are grunty enough to handle a fair amount of GRE traffic, but not if they are sustaining/filtering a DDOS attack at the same time.<br></div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><br></div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color:
transparent; font-style: normal;"><br></div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;">regards,</div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;">Tony.<br>
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<div><span><br class=""></span></div><div><br></div> <div class="" style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 12pt;"> <div class="" style="font-family: times new roman, new york, times, serif; font-size: 12pt;"> <div dir="ltr"> <hr size="1"> <font face="Arial" size="2"> <b><span style="font-weight:bold;">From:</span></b> "joe@apcs.com.au" <joe@apcs.com.au><br> <b><span style="font-weight: bold;">To:</span></b> ausnog@lists.ausnog.net <br> <b><span style="font-weight: bold;">Sent:</span></b> Friday, 3 January 2014 4:49 PM<br> <b><span style="font-weight: bold;">Subject:</span></b> [AusNOG] Cisco GRE Tunnel weirdness<br> </font> </div> <div class=""><br>Hi List,<br><br> I have a GRE tunnel between 2 sites over a link limited to 1500 MTU.<br><br> As such we have mtu set to 1440 and mss-adjust to 1400 on both ends. <br>This is overly cautious probably but it was
working.<br><br> Anyway - it had been working quite fine for some time, but randomly we <br>started seeing massive performance issues. Bandwidth throughput halved <br>and ping times sky rocketed (~50ms to ~1000ms). We tried bringing down <br>the tunnel and back up, no luck, and even power cycled each end (Cisco <br>3945's), no luck.<br><br> We have confirmed that the config's had not been changed for weeks. <br>Neither end had crashed and rebooted. The tunnel itself did not go down <br>between 'working' and 'not working'. Performance and ping times via the <br>tunnel endpoint address' is fine, proving (to me) that the networks <br>between the 2 sites are not the issue, but the tunnel itself. No links <br>are saturated, and CPU performance is quite tame (both before and during <br>the issue)<br><br> For now we have gone back to backup path but I haven't been able to <br>find similar problems online, and my own Cisco tunnel experience
leaves <br>me empty so far.<br><br> Has anyone experienced a similar issue? A working tunnel suddenly <br>having major performance issues?<br><br>Thanks,<br>Joe<br>_______________________________________________<br>AusNOG mailing list<br><a ymailto="mailto:AusNOG@lists.ausnog.net" href="mailto:AusNOG@lists.ausnog.net">AusNOG@lists.ausnog.net</a><br><a href="http://lists.ausnog.net/mailman/listinfo/ausnog" target="_blank">http://lists.ausnog.net/mailman/listinfo/ausnog</a><br><br><br></div> </div> </div> </div></body></html>