Odd router brokenness

Keegan Holley keegan.holley at sungard.com
Wed Nov 23 10:41:34 CST 2011


2011/11/23 Saku Ytti <saku at ytti.fi>

> On (2011-11-23 09:41 -0500), Mark Radabaugh wrote:
>
> > The question is:   How does a router break in this manner?    It
> > appears to unintentionally be doing something different with traffic
> > based on the source address, not the destination address.    I
> > realize this can be done intentionally  - but that is not the case
> > here (unless somebody isn't telling me something).
>
> I don't think we can determine that it has anything to do with source
> address based on data shown.
> 38.104.148.5 could very well be 6500 and somehow broken adjacency to
> 74.125.226.6, perhaps hardware adjacency having MTU of 0B, causing punt
> which is rate-limited by different policer than TTL exceeded policer.
>
>
> Agree.  I've seen similar effects with a different ISP who had one side of
an ether-channel go south without the port showing down.  Stuff hashed over
the good like was fine, stuff hashed over the bad like wasn't.  Led to some
painful support calls from customers.  I agree this list is a haven of
speculation and OT comments.  In order to avoid making a bad problem worse
you should probably contact cogent.


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