Anyone from Level3/CenturyLink/Lumen, possibly Comcast around?

Pennington, Scott scott.pennington at
Fri Oct 15 16:48:20 UTC 2021

We have also seen the same behavior of intermittent customer complaint followed by issue resolving spontaneously.   Our end customer has a tunnel to a supplier on Comcast with a return path via Lumen.   The first ticket was opened on 9/23, has cleared and returned a few times.  End customer worked with Cisco TAC and symptom is up to 30% ESP packet drop for periods from 5 minutes to 1 hour when the problem is active.

From: NANOG < at> on behalf of Mike Lewinski via NANOG <nanog at>
Sent: Thursday, October 14, 2021 2:30 PM
To: Brie <bruns at>; nanog at <nanog at>
Subject: RE: Anyone from Level3/CenturyLink/Lumen, possibly Comcast around?

I can confirm this issue exists at several sites in the Denver area with this same IPSEC issue, all routing between Level3/Lumen and Comcast.

I was told by one customer that it resolved late yesterday afternoon but I haven't been able to confirm that.


-----Original Message-----
From: NANOG < at> On Behalf Of Brie
Sent: Thursday, October 14, 2021 10:43 AM
To: nanog at
Subject: Anyone from Level3/CenturyLink/Lumen, possibly Comcast around?

Hi all,

So, having a...  frustrating issue going on.  Long wall of text ahead as I explain.

1 x CenturyLink/Lumen fiber in Boise
1 x CenturyLink/Lumen fiber in Cheyenne
1 x Comcast biz fiber in Denver

IPsec VPN tunnels between all three sites, w/ OSPF for routing failover (which unfortunately doesn't help in this situation).

Two days ago, Cheyenne to Denver (.196) traffic (both tcp and udp) were an issue initially.  Failed over to routing Cheyenne VPN through Boise while we opened ticket with CL.

Yesterday, Boise to Denver (.196) traffic started having exact same issue.

Tests from another CL fiber in Boise (my own circuit, with legacy IP space and BGP) to Denver (.196) did not show same issues.  Path appeared clean.

Traceroutes from Office Boise to Denver (.196) had a noticeable difference from Personal Boise to Denver (.196):

Office Boise -> Denver (.196)
5:   <------  This hop

Personal Boise -> Denver (.196)

On a whim, tracerouted to another Denver router IP address (.199, IP alias on same interface) from Boise Office, and traceroute matched the traceroute from Personal Boise to Denver (.196) traceroute.

No packet loss.

Swapped VPN tunnels over to using another ip on same router (.199), same interface physical and logical, in Denver, and VPN was working again normally.

This morning though, Cheyenne to Denver (.199) is having problems, while Boise to Denver (.199) isn't (for now).

Already spent most of last night working with my partner in Denver replacing nearly everything on the Denver side with no change.

Tests from the router above the main Denver VPN endpoint (.196) do not show any kind of issues or packet loss to it, so it doesn't appear the problem is inside of our network.

I'm not inclined to think this is a Comcast issue, but I can't be sure.

This sounds almost like a load balancing hashing issue, with one link in the bond group having issues, somewhere in one of our upstream's networks.

We'll be opening a ticket in a bit through normal channels with CenturyLink/Lumen, but we're worried they're just going to close the ticket as not being their issue.

Anyone know of an engineer at CenturyLink/Lumen/Level3 or even Comcast that might want to take a stab at this?  I can provide a lot more detail.

Brielle Bruns
The Summit Open Source Development Group    /
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