Long AS Path

Wed Jun 21 16:42:56 UTC 2017

My cut off is 6 ASNs - more than 6 and it never makes it to the FIB.

However, for this to be viable with plenty of unique prefixes to maintain
a large table, we have lots and lots of direct big and small peers and
much more than the usual amount of transit neighbors in our network.
Silicon Valley companies are very demanding for the fasted path with the
lowest number of router hops. ASN hops almost always lead to more router
hops in the trace. We have customers that call us if everything is fine
and they want to shave off milliseconds to favorite destinations. Picky,
picky, picky.

I am wondering how may other networks get requests (more like demands)
from customers wanting you to speed packets up to and from a specific
office in India or China. Customers knowing nothing about their office ISP
overseas. BTW, it's almost always they have the cheapest congested shared
office connection in the building overseas (especially in India). So they
can't do anything there except "pretend" about the bandwidth available.
About all they know is the IP address of the VPN and they were told they
have a full gig connection. Sure they have a gig port, but it's on a
switch together with 10 building neighbors that all also have a gig port
on a circuit to the building that no one can maintain a gig for more than
3 ms. Go ahead try and fix that latency packet dropping issue with a
firewall on both ends with SPI turned on in both directions.  It's your
fault if you cant make it better. After all their VPN from London to
Bangalore works fine. And the ones in China all work fine to and from
Australia.

Anyways, I always wondered is it just me or do others get these kind of
requests?

Thank You
Bob Evans
CTO

> Steinar,
>
> What reason is there to filter them? They are not a significant fraction
> of BGP paths. They cause no harm. It's just your sense of tidiness.
>
> You might consider contacting one of the operators to see if they do have
> a good reason you haven't considered. But absent a good reason *to* filter
> them, I would let BGP mechanics work as intended.
>
>  -mel beckman
>
> On Jun 21, 2017, at 12:57 AM, "sthaug at nethelp.no" <sthaug at nethelp.no>
> wrote:
>
>>> Just wondering if anyone else saw this yesterday afternoon ?
>>>
>>> Jun 20 16:57:29:E:BGP: From Peer 38.X.X.X received Long AS_PATH=3D
>>> AS_SEQ(2=
>>> ) 174 12956 23456 23456 23456 23456 23456 23456 23456 23456 23456 23456
>>> 234=
>>> 56 23456 23456 23456 23456 23456 23456 23456 23456 23456 23456 23456
>>> 23456 =
>>> 23456 23456 23456 23456 23456 ... attribute length (567) More than
>>> configur=
>>> ed MAXAS-LIMIT
>>
>> There are quite a few examples of people using stupidly long AS paths.
>> For instance
>>
>> 177.23.232.0/24    *[BGP/170] 00:52:40, MED 0, localpref 105
>>                      AS path: 6939 16735 28163 28163 28163 28163 28163
>> 28163 28163 28163 28163 28163 28163 28163 28163
>> 28163 28163 28163 262401 262401 262401 262401
>> 262401 262401 262401 262401 262401 262401 262401
>> 262401 262401 262401 262401 262401 262949 52938
>> 52938 52938 52938 52938 52938 52938 52938 52938
>> 52938 52938 I
>>
>> I currently have 27 prefixes in my Internet routing table with 40 or
>> more ASes in the AS path (show route aspath-regex ".{40,}").
>>
>> I see no valid reason for such long AS paths. Time to update filters
>> here. I'm tempted to set the cutoff at 30 - can anybody see a good
>> reason to permit longer AS paths?
>>
>> Steinar Haug, Nethelp consulting, sthaug at nethelp.no
>