Equipment (Modems,Gateways)
Modems, Gateways, and Networking Devices
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Need Gateway set to True Bridged Mode

Hi, We are adding our office to our corporate network and will be using a Clavister E5 attached to the Comcast IP gateway. We have a single static IP and the E5 is configured to take over once our IP gateway has been configured for true bridge mode.

 

Could I ask that someone makes that change?

 

Regards,

 

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Re: Need Gateway set to True Bridged Mode

To explain a little better comcast has a unique way of handling static IP addresses.

Your modem still gets a DHCP address from Comcast but with a Static IP the extra step of updating the RIP tables in the Comcast routers take place.

 

Lets say for instance your static IP was x.x.x.x 

Your comcast modem receives a DHCP address of y.y.y.y

It updates the Comcast RIP router to say the next hop to x.x.x.x is y.y.y.y

This way your router receives your traffic and routes it to your IP address.  

Because of this extra routing there really is no true bridge mode on Comcast equipment.  This is also why you must rent a modem if you have static IPs, Comcast must be able to control the security of the RIP updates.

 

I have never deait with the block of one IP but with my block of 5 IPs I can use my external IP addresses (x.x.x.1-5) on the wan side with no issue.  They are statically set though.  There is always a 10.1.10.1 network and if I use that network the traffic goes out on the gateway address effectively giving you 6 ip addresses (5 static IPs and the gateway) if you are ok with the modem doing the routing.

 

I hope that helps clear things up.

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Re: Need Gateway set to True Bridged Mode

Hello rmj and welcome,

 

If you have a static IP then your modem cannot be put in "True Bridge Mode or Just Pass-Thru" due to all of your routing will be disabled. There is no issue with disabling the Comcast Gateway DHCP Server to avoid any DHCP server conflicts with your Clavister E5 DHCP Server. 

 

Hope this helps you out.

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Re: Need Gateway set to True Bridged Mode

Hi,

 

I only have one static IP, so I just need the Clavister to receive that. This is how we have done it on our other offices around the world. Why would it not work here - Clavister is the router and we have V3 and V5's at the other offices, but decided to go with E5 in the smaller US office.

 

Thanks

 

René

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Contributor

Re: Need Gateway set to True Bridged Mode

To explain a little better comcast has a unique way of handling static IP addresses.

Your modem still gets a DHCP address from Comcast but with a Static IP the extra step of updating the RIP tables in the Comcast routers take place.

 

Lets say for instance your static IP was x.x.x.x 

Your comcast modem receives a DHCP address of y.y.y.y

It updates the Comcast RIP router to say the next hop to x.x.x.x is y.y.y.y

This way your router receives your traffic and routes it to your IP address.  

Because of this extra routing there really is no true bridge mode on Comcast equipment.  This is also why you must rent a modem if you have static IPs, Comcast must be able to control the security of the RIP updates.

 

I have never deait with the block of one IP but with my block of 5 IPs I can use my external IP addresses (x.x.x.1-5) on the wan side with no issue.  They are statically set though.  There is always a 10.1.10.1 network and if I use that network the traffic goes out on the gateway address effectively giving you 6 ip addresses (5 static IPs and the gateway) if you are ok with the modem doing the routing.

 

I hope that helps clear things up.

View solution in original post

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Re: Need Gateway set to True Bridged Mode

Hi Tnelsom

 

Thank you for that. I have talked with our coporate IT, and they informed me, that as long as I can use the static IP address directly - so simple pass through and any traffic that goes to the static IP is passed on to the Clavister device then I should be fine. The question now is if I can set that up on the Comcast IP gateway myself using the management interface. Can you provide me with what I need to configure - I know it is a lot to ask, but I am not used to doing it this way.

 

Basically I have one static IP, and I need all traffic to go to the Clavister with no NAT in between, so the Clavister will need to "logically" think it has that static public IP on the WAN side. Is that possible without having Comcast do any changes?

 

Thanks again

 

René

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Re: Need Gateway set to True Bridged Mode

It sounds like you may not be using your ip addresses correctly either. With our comcast block of 5 ips we did this. (Obviously 172.16.0.x is not our ip but you get the idea)
172.16.0.6 comcast modem gateway
Block of ips 172.16.0.1 - 172.16.0.5

Cisco router directly connected to the modem statically set to
IP address. 172.16.0.1 (first usable IP address)
Subnet mask 255.255.255.248
Gateway 172.16.0.6

Linux spam filter directly connected to the modem statically set to
IP address 172.16.0.2 (second usable static IP address)
Subnet 255.255.255.248
Gateway 172.16.0.6

Using your ip addresses this way eliminates the need for 1 to 1 nat and eases the load on the modem.

Tip: If you setup a device using the modem 10.1.10.1 network the traffic will go out on the gateway device giving you a 6th IP address.
Example
Linksys wireless router
IP address 10.1.10.10
Subnet mask 255.255.255.0
Gateway 10.1.10.1
This will have a public IP address of 172.16.0.6 and in this case if I wanted to enable outside traffic to access my wireless router I can do a 1 to 1 nat.
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