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Comcast Bussiness Class and GRE Tunnels

On Jul 26, 2011, at 11:07 37AM, Nate Burke wrote:

> 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.
I had to make the LAN end of the tunnel the "DMZ host" (under Firewall settings on my SMC).

		--Steve Bellovin, https://www.cs.columbia.edu/~smb