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Evanston, IL

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[Speed] Comcast HSI 50/10 Docsis 3 w/ SMC D3G issues solved

Ordered Comcast 50/10 with 12 Static IPs, Arrived with SMC D3G Gateway, had many issues getting this to perform as advertised but once we worked out the issues it does a solid 50/10 24x7. Here are a few tips for setting one of these up: Disclaimer this post is intended for network professionals that are familiar with routing and TCP/IP!
First: the device has an auto sense issue with setting 10/100/1000 full line speeds, it likes to reset to 10/half for no reason, we found the only way to guarantee a line speed is to allow it to auto negotiate and set both sides of the link to auto, un-checking the "auto" box never worked. check the box for auto and set a line speed as well and hit apply a few times, you may need to hit apply a couple of times before it takes as I suspect until it syncs with the far side it will continuously reset itself to 10/half until it locks a speed.
Second: If you receive static IPs do NOT set the internal lan IP on the SMC to one of your static IPs, you will get unexpected results and speed issues. Strangely that internal LAN value is worthless unless you are doing DHCP/NAT in the SMC, only configure this if you are using the SMC to translate hosts.
If you are using an external Firewall for NAT/DHCP, set one of your static ips on your host or seperate Firewall (Pix, Sonic Wall) and set the default gateway as the gateway comcast gave you not the inside LAN IP, again do not set any of your statics or the default gateway address as the inside lan IP on the SMC, the SMC gateway will route the static addresses regardless. Only use the inside LAN IP address on the SMC for a NAT range if you need DHCP/NAT, that is its only purpose.
Third: if you are using an external firewall (Pix, Sonic Wall) turn off all packet inspection and NAT within the SMC. These are check boxes within the configuration. Again set your outside address on your external firewall to one of your statics IPs, you do not need to configure an IP on the SMC side of this link, as I stated that internal lan IP on the SMC has no bearing on static IPs or routing from your external firewall. Set your outbound route or gateway of last resort on your external firewall to the gateway address comcast gave you. Also set your external Firewall to NAT/PAT your internal hosts to the Static IP you set on the outside interface. You cannot set your external firewall to NAT to a dynamic Comcast address. I wanted to have my non static NAT'ed internal hosts to pull a Comcast dynamic public IP but was unable to get this working. This seems to only work in the SMC and not seperate NAT device.
Lastly: Make sure all interfaces are running at 100mb or 1000mb, and all interfaces must be also be full duplex, 10mb or any half duplex interface will kill DOCSIS 3 speeds.
Once this is all complete do a speed test at »speedtest.comcast.net, you should see 50/10 for all your NAt'ed hosts on the SMC or your external firewall. Then setup any 1 for 1 static NATs on the SMC or your firewall depending on your configuration.
If you still have problems and you are a business customer contact the Comcast Twitter team, this is a better avenue than calling the 800 number, you will get hooked up with someone who actually knows that device and TCPIP. So in short this device works, it just is very finicky and must be configured in a very specific way. But I can attest I have over 100 Macs and PCs getting 50/10 - 24x7 and static IPs available for 11 of my machines. DOCSIS 3 is awesome and I highly recommend it for businesses with under 300 machines, we are unable to push the pipe past 38mb/sec with 100 machines on it and that was trying to max it out.

Mod Note: This post is now linked in the first post of the stickied DOCSIS 3 topic. Please keep further discussion in that thread. Thanks, sorto'.

»Is the DOCSIS 3 rollout complete in your area? Post here.