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Comcast Bussiness Class and GRE Tunnels

I had to deal with this Exact problem last week. Never got EOIP to work, 
Spent hours on it.

I had to use a "GRE Tunnel" Which is the same thing. And is only available 
under RouterOS 5.x+. Came right up when EOIP wouldn't. I don't know how to 
peg the problem. As PPTP, EOIP, GRE...etc All use the GRE protocol 47. So 
you would think they all would show the same problem.

I never even attempted to contact comcast support as I wasn't about to 
spend another 3 hours explaining my problem only for them to say they 
aren't blocking anything and it must be my side.. 

Nick Olsen

Network Operations
(855) FLSPEED  x106


From: "Nate Burke" <nate at blastcomm.com>

Sent: Tuesday, July 26, 2011 11:07 AM

To: "NANOG list" <nanog at nanog.org>

Subject: Comcast Bussiness Class and GRE Tunnels

Hello, I'm hoping that someone here might have run into a similar issue 

and might be able to offer me some pointers.

I have a customer that I am providing redundant paths to, one link over 

a microwave connection, and a backup link over a Comcast Business Class 

Connection.  Everything on the Microwave link is working fine.  On the 

Comcast Connection, I have a Static IP from Comcast, and I want to setup 

a vendor specific GRE tunnel (Mikrotik EoIP) from my NOC to the Comcast 

Static IP Address.  It looks like the SPI Firewall inside the SMC 

Gateway required by comcast is blocking the GRE packets, I'm basing this 

on the fact that when I power cycle the modem, I get 1 ICMP Packet 

through the GRE Tunnel while the modem is booting up, then it stops 

again.  I have gotten to Tier2 support who swears that all Firewalls on 

the SMC Gateway are disabled.

As a workaround, I was able to establish a PPTP tunnel to my NOC, 

however it seems like the tunnel will only run for a few hours, then 

becomes slow to the point of being unusable.  In my mind this would be 

no different than setting up a permanent VPN back to a corporate office, 

which I would think happens all the time, so I'm not sure why I'm 

running into issues with it.

Anyone with Insights or comments would be appreciated.


Nate Burke