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Re: comcast routing issue question
- From: Matthew Petach
- Date: Thu Nov 30 15:27:53 2006
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On 11/29/06, Jim Popovitch <jimpop@yahoo.com> wrote:
On Thu, 2006-11-30 at 00:06 -0500, Jim Popovitch wrote:
> Question: What could cause the first trace below to succeed, but the
> second trace to fail?
>
> $ mtr 69.61.40.35
> HOST: blue Loss% Snt Last Avg Best Wrst
> 1. 192.168.3.1 0.0% 1 4.3 4.3 4.3 4.3
> 2. 73.62.48.1 0.0% 1 10.6 10.6 10.6 10.6
> 3. 68.86.108.25 0.0% 1 11.4 11.4 11.4 11.4
> 4. 68.86.106.54 0.0% 1 9.8 9.8 9.8 9.8
> 5. 68.86.106.9 0.0% 1 20.5 20.5 20.5 20.5
> 6. 68.86.90.121 0.0% 1 11.3 11.3 11.3 11.3
> 7. 68.86.84.70 0.0% 1 27.7 27.7 27.7 27.7
> 8. 64.213.76.77 0.0% 1 24.5 24.5 24.5 24.5
> 9. 208.50.254.150 0.0% 1 39.4 39.4 39.4 39.4
> 10. 208.49.83.237 0.0% 1 46.6 46.6 46.6 46.6
> 11. 208.49.83.234 0.0% 1 40.7 40.7 40.7 40.7
> 12. 69.61.40.35 0.0% 1 43.9 43.9 43.9 43.9
>
> $ mtr 69.61.40.34
> HOST: blue Loss% Snt Last Avg Best Wrst
> 1. 192.168.3.1 0.0% 1 1.1 1.1 1.1 1.1
> 2. 73.62.48.1 0.0% 1 9.9 9.9 9.9 9.9
> 3. 68.86.108.25 0.0% 1 9.3 9.3 9.3 9.3
> 4. 68.86.106.54 0.0% 1 9.6 9.6 9.6 9.6
> 5. 68.86.106.9 0.0% 1 9.0 9.0 9.0 9.0
> 6. 68.86.90.121 0.0% 1 18.2 18.2 18.2 18.2
> 7. 68.86.84.70 0.0% 1 23.9 23.9 23.9 23.9
> 8. ??? 100.0 1 0.0 0.0 0.0 0.0
>
>
> Taking the 69.61.40.33/28 subnet a bit further, .36 drops at 68.86.84.70
> but .37 - .39 make it. .40 drops at 68.86.84.70, but .41 makes it.
>
> Crazy.
Btw, the problem has now been resolved, however I'm still curious as to
what scenario could have caused that.
-Jim P.
eBGP multihop peering across a pair of 10 gigE links with
static routes pointing to the remote router loopback; one
link goes south, but the interface still shows as up/up,
and voila, depending upon the hash, your packets may
go across the good link, or they may disappear into the
black hole of oblivion.
This is why multipath is a good thing, and eBGP multihop
with static routes is a Bad Thing(tm).
Matt
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