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AfNOG2005 Troubleshooting BGP

Apr 07, 2018

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    Troubleshooting Connectivity

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    979797 2005, Cisco Systems, Inc. All rights reserved.APRICOT2005

    Troubleshooting Connectivity Example IV

    Checklist:Assume AS1 has done everything in thistutorial so far

    L2 problem? Route Flap Damping?

    All the configurations look fine, the Looking Glassoutputs look fine, life is wonderful Apart from thoseannoying traffic swings every hour or so

    Since BGP is configured fine, and the net has beenstable for so long, can only be an L2 problem, orRoute Flap Damping side-effect

    Troubleshooting Connectivity

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    989898 2005, Cisco Systems, Inc. All rights reserved.APRICOT2005

    g yExample IV

    L2 upstream somewhere has poorconnectivity between themselves and therest of the Internet

    Only real solution is to impress uponupstream that this isnt good enough, and getthem to fix it

    Or change upstreams

    Troubleshooting Connectivity

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    999999 2005, Cisco Systems, Inc. All rights reserved.APRICOT2005

    g yExample IV

    Route Flap DampingMany ISPs implement route flap damping

    Many ISPs simply use the vendor defaults

    Vendor defaults are generally far too severe

    There is even now some real concern that the morelenient RIPE-229 values are too severe

    www.cs.berkeley.edu/~zmao/Papers/sig02.pdf

    Again Looking Glasses come to the operators

    assistance

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    100100100 2005, Cisco Systems, Inc. All rights reserved.APRICOT2005

    Troubleshooting Connectivity

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    101101101 2005, Cisco Systems, Inc. All rights reserved.APRICOT2005

    g yExample IV

    Most Looking Glasses allow the operators tocheck the flap or damped status of theirannouncements

    Many oscillating connectivity issues are usually caused

    by L2 problemsRoute flap damping will cause connectivity to persistvia alternative paths even though primary paths havebeen restored

    Quite often, the exponential back off of the flapdamping timer will give rise to bizarre routing

    Common symptom is that bizarre routing will often clearaway by itself

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    102102102 2005, Cisco Systems, Inc. All rights reserved.APRICOT2005

    Troubleshooting Summary

    Most troubleshooting is about:

    ExperienceRecognising the common problems

    Not panicking

    Logical approachCheck configuration first

    Check locally first before blaming the peer

    Troubleshoot layer 1, then layer 2, then layer 3, etc

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    103103103 2005, Cisco Systems, Inc. All rights reserved.APRICOT2005

    Troubleshooting Summary

    Most troubleshooting is about:

    Using the available tools

    The debugging tools on the router hardwareInternet Looking Glasses

    Colleagues and their knowledge

    Public mailing lists where appropriate

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    104104104 2005, Cisco Systems, Inc. All rights reserved.APRICOT2005

    Closing Comments

    Presentation has covered the most

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