[afnog] Problem accessing some sites

[Jens Kuehlers]

Hi!
Having a reverse traceroute from the sites you cannot reach often helps to
resolve these problems.

I suggest checking http://www.traceroute.org and running traceroutes from
different sites listed there.
Often problems like this is because you or your client have uRPF (Unicast
Reverse Path Forwarding) enabled, this becomes a problem with asymmetric
routing which can happen once you multihome. Please check that this is not
enabled for either you or your client.

Jens




On Thu, Aug 11, 2011 at 06:56, mike otieno <otienomike at gmail.com> wrote:

> Hi
>
> I need some help with a problem am experiencing in my network.
> I have a client that am giving transit, and he has two fiber paths to our
> core routers.
> Path A connects to router A on my network.
> Path B connects to a different router B on my network.
>
> On path A; All the prefixes are working perfectly and accessing all
> internet sites.
>
> On path B; The prefixes can open some sites and not others like; yahoo.com,
> .uk. fr and http://www.tvchannelsfree.com/. Now i have a more specific
> block /24 advertised on this path and its uplink is preferring this path as
> the best, same with the down-link. As i get this from all looking glasses.
> To eliminate double advertisement we even shut down BGP via path A.
> A trace from this client to yahoo with the source ip advertised via this
> path B, gets lost on the 14th hop and beyond. See below trace;
>
> Tracing the route to yahoo.com (72.30.2.43)
>
>   1 41.215.251.42 0 msec 0 msec 4 msec
>   2 41.84.146.13 [AS 33770] 212 msec 208 msec 212 msec
>   3  *  *  *
>   4 ae-34-52.ebr2.London1.Level3.net (4.69.139.97) [AS 33770] 208 msec 208
> msec 208 msec
>   5 ae-41-41.ebr1.NewYork1.Level3.net (4.69.137.66) [AS 33770] 280 msec
>     ae-42-42.ebr1.NewYork1.Level3.net (4.69.137.70) [AS 33770] 276 msec
>     ae-44-44.ebr1.NewYork1.Level3.net (4.69.137.78) [AS 33770] 280 msec
>   6 ae-91-91.csw4.NewYork1.Level3.net (4.69.134.78) [AS 33770] 284 msec
>     ae-61-61.csw1.NewYork1.Level3.net (4.69.134.66) [AS 33770] 288 msec
> 280 msec
>   7 ae-72-72.ebr2.NewYork1.Level3.net (4.69.148.37) [AS 33770] 276 msec
>     ae-92-92.ebr2.NewYork1.Level3.net (4.69.148.45) [AS 33770] 280 msec
>     ae-72-72.ebr2.NewYork1.Level3.net (4.69.148.37) [AS 33770] 276 msec
>   8 ae-2-2.ebr4.SanJose1.Level3.net (4.69.135.185) [AS 33770] 348 msec 344
> msec 344 msec
>   9 ae-61-61.csw1.SanJose1.Level3.net (4.69.153.2) [AS 33770] 352 msec
>     ae-91-91.csw4.SanJose1.Level3.net (4.69.153.14) [AS 33770] 348 msec
>     ae-71-71.csw2.SanJose1.Level3.net (4.69.153.6) [AS 33770] 344 msec
>  10 ae-43-90.car3.SanJose1.Level3.net (4.69.152.197) [AS 33770] 344 msec
> 348 msec
>     ae-23-70.car3.SanJose1.Level3.net (4.69.152.69) [AS 33770] 344 msec
>  11 YAHOO-INC.car3.SanJose1.Level3.net (4.71.112.14) [AS 33770] 348 msec
> 344 msec 348 msec
>  12 ae-0-d221.msr1.sk1.yahoo.com (216.115.106.139) [AS 33770] 348 msec
>     ae-0-d231.msr2.sk1.yahoo.com (216.115.106.143) [AS 33770] 384 msec
>     ae-0-d221.msr1.sk1.yahoo.com (216.115.106.139) [AS 33770] 344 msec
>  13 te-9-1.bas-k1.sk1.yahoo.com (68.180.160.13) [AS 33770] 348 msec
>     te-8-1.bas-k2.sk1.yahoo.com (68.180.160.11) [AS 33770] 348 msec
>     te-9-1.bas-k1.sk1.yahoo.com (68.180.160.13) [AS 33770] 348 msec
>  14  *  *  *
>  15  *  *  *
>  16  *  *  *
>  17  *  *  *
>   18  *  *  *
>  19  *
>
> Please help out with ideas as to why i am experiencing this.
> --
> Rgds
> Michael Otieno
>
>
>
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>



-- 
Jens Kuehlers | Technical Program Manager, Google Ghana |
kuehlers at google.com | +233 265 661408
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