Issues with 4-octet BGP AS and Akamai?

Greg Gombas -X (grgombas) grgombas at
Tue Nov 14 19:02:19 UTC 2017

Hi Tyler,

Unfortunately we had a limited window to test so could not check the reverse path.

During our failover testing we stopped advertising out the primary path and only advertised out the secondary path. Routes are advertised out the secondary path through a DDOS prevention company called F5 Silverline which is reached via a GRE tunnel running over the Optimum Lightpath network.

So outgoing traffic would go from NYULH going out the Optimum Lightpath circuit and return traffic coming in on F5 Silverline’s network then tunneled over Optimum Lightpath back to NYULH.
So traffic was definitely routing asymmetrically.

However F5 Silverline assured us they have many customers using a similar setup but have no issues with Akamai.

I would think that many customers using similar DDOS prevention services such as F5 Silverline and Prolexic are routing asymmetrically as well, wouldn’t uRPF be affecting them all?


Gregory Gombas
CCIE# 19649 – R&S
Network Consulting Engineer
Advanced Services
grgombas at<mailto:grgombas at>
Office: +1-212-714-4497
Mobile: +1-201-675-9457

Cisco Systems Limited
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From: Tyler Conrad [mailto:tyler at]
Sent: Tuesday, November 14, 2017 1:30 PM
To: james machado <hvgeekwtrvl at>
Cc: Greg Gombas -X (grgombas) <grgombas at>; nanog at
Subject: Re: Issues with 4-octet BGP AS and Akamai?

Are you advertising out multiple circuits? Check the pathing both directions if you can. A lot of CDNs enforce uRPF strict.

On Tuesday, November 14, 2017, james machado <hvgeekwtrvl at<mailto:hvgeekwtrvl at>> wrote:

I have a 4 byte ASN and have not had any issues with reach ability,
including the 2 websites you have linked.


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