Comcast gateway LAN/router LAN conflict?



  • Hi guys,

    I have a new customer that has internet download speeds that vary wildly during the day. Sometimes endpoints (wired) get 89-90 Mbps, while other times of the day they get as low as 10 Mbps. Any time you test the connection directly off the Comcast gateway you get speeds of 80-90 Mbps.

    This is how their setup is wired:

    Comcast gateway (10.1.10.1 LAN) -> WAN port (configured to use Comcast static IP) of Luxul XBR-4400 router. The Luxul router's LAN IP is 10.1.10.2 and is their DHCP server. The router is setup to use a static IP address from Comcast on the WAN side so it's not getting a 10.1.10.X IP from the Comcast Gateway's DHCP server.

    I've always setup my customers with unique IP addresses for their LAN. Is there a potential conflict with the LAN side of the Comcast gateway with the LAN side of the Luxul router?

    If not, my guess is that the Luxul router is having some sort of weird issue.



  • Uhm, that would be a problem. You want a different subnet on the LAN side than what the XBR-4400 is assigned on the WAN side, which seems to be 10.1.10.X on both sides if I've understood you correctly.


  • Service Provider

    Definitely no routing there. That's a problem.



  • @travisdh1 Just to be clear...the router is configured for a WAN static IP from comcast, so the IP address on the routers WAN is different from the router's LAN.


  • Service Provider

    @frodooftheshire said in Comcast gateway LAN/router LAN conflict?:

    Hi guys,

    I have a new customer that has internet download speeds that vary wildly during the day. Sometimes endpoints (wired) get 89-90 Mbps, while other times of the day they get as low as 10 Mbps. Any time you test the connection directly off the Comcast gateway you get speeds of 80-90 Mbps.

    This is how their setup is wired:

    Comcast gateway (10.1.10.1 LAN) -> WAN port (configured to use Comcast static IP) of Luxul XBR-4400 router. The Luxul router's LAN IP is 10.1.10.2 and is their DHCP server. The router is setup to use a static IP address from Comcast on the WAN side so it's not getting a 10.1.10.X IP from the Comcast Gateway's DHCP server.

    I've always setup my customers with unique IP addresses for their LAN. Is there a potential conflict with the LAN side of the Comcast gateway with the LAN side of the Luxul router?

    If not, my guess is that the Luxul router is having some sort of weird issue.

    This is bad design. You are using the same subnet. I cannot believe you have not had more problems.

    If the ISP hardware is on 10.1.10.0/24 you should most certainly not put your LAN on the same subnet.
    Fix your LAN.



  • @JaredBusch As a quick fix I had planned to quickly change the LAN subnet of the Comcast equipment to something like 10.1.1.X, but long term I want to get all the LAN devices on a unique IP addressing scheme to reduce the possibilities down the road - for example if Comcast replaces his box with another box that will use the 10.1.10.X scheme.


  • Service Provider

    @frodooftheshire said in Comcast gateway LAN/router LAN conflict?:

    @travisdh1 Just to be clear...the router is configured for a WAN static IP from comcast, so the IP address on the routers WAN is different from the router's LAN.

    does not matter. The Comcast hardware answers all things on 10.1.10.0/24

    Your router is only SHARING the WAN IP. This the comcast system still uses it also. As well as the 10.1.10.0/24 network. This is how this stuff works and why you are required to use their gear.


  • Service Provider

    @frodooftheshire here is a good description form AT&T on the subject of IP passthrough. It is basically the same for Comcast. They are not going to route two networks to every basic business customer in order to let you truly have your own full public IP.

    IP Passthrough means the AT&T supported CPE device terminates the DSL, authenticates with the network (Receives a WAN IP) and shares that IP address with a single device connected to the AT&T supported CPE equipment. This configuration is often times suitable for a business customer desiring to connect third party equipment to AT&T supported equipment. The "IP Passthrough configuration still allows AT&T support groups to access the AT&T supported equipment while allowing end-users to connect third party equipment in a configuration they desire. The "IP Passthrough" configuration will only allow one connection to AT&T supported equipment to be "unfiltered" or pingable from the WAN or internet side of the AT&T equipment (does not support multiple pingable connections).


  • Service Provider

    @frodooftheshire said in Comcast gateway LAN/router LAN conflict?:

    @travisdh1 Just to be clear...the router is configured for a WAN static IP from comcast, so the IP address on the routers WAN is different from the router's LAN.

    The IP is different, but is the network different? What's the subnet?



  • @scottalanmiller Sorry, I should have been more clear there. The static IP on the luxul's WAN side is 50.193.X.X /30. The lan side on the Comcast is 10.1.10.0/24 and the lan on the Luxual is the same 10.1.10.0/24


  • Service Provider

    @frodooftheshire said in Comcast gateway LAN/router LAN conflict?:

    @scottalanmiller Sorry, I should have been more clear there. The static IP on the luxul's WAN side is 50.193.X.X /30.

    it is not a static IP

    @frodooftheshire said in Comcast gateway LAN/router LAN conflict?:

    The lan side on the Comcast is 10.1.10.0/24 and the lan on the Luxual is the same 10.1.10.0/24

    this is completely the problem.



  • @frodooftheshire said in Comcast gateway LAN/router LAN conflict?:

    @scottalanmiller Sorry, I should have been more clear there. The static IP on the luxul's WAN side is 50.193.X.X /30. The lan side on the Comcast is 10.1.10.0/24 and the lan on the Luxual is the same 10.1.10.0/24

    Time to try my ASCII art so we can visualize this:

       Comcast          Luxual           Local Net
    10.1.10.0/24 --> 50.193.x.x/30  --> 10.1.10.0/24
    

    I'd say you need to change the local subnet or get a new subnet from Comcast, either way works. Probably easier to change the Local Net.



  • @travisdh1 it's way easier to change the LAN subset on the Comcast which a is a quick fix. The long term fix would be to change the LAN IP scheme behind the luxul. They have a lot of misc devices with static IPs on the LAN that would all have to get updated.



  • @JaredBusch They pay for a dedicated static IP from Comcast. What would you call it if not a static IP?



  • @frodooftheshire said in Comcast gateway LAN/router LAN conflict?:

    @travisdh1 it's way easier to change the LAN subset on the Comcast which a is a quick fix. The long term fix would be to change the LAN up scheme behind the luxul. They have a lot of misc devices with static IPs on the LAN that would all have to get updated.

    I generally avoid calling Tier 1 support from my ISP whenever possible, it always feels like walking into the dragon's lair.



  • @frodooftheshire said in Comcast gateway LAN/router LAN conflict?:

    @JaredBusch They pay for a dedicated static IP from Comcast. What would you call it if not a static IP?

    Can you ping that 50.193.x.x address from outside your local network?



  • @travisdh1 yes. I can ping the Comcast's gateway IP and the usable IP configured on the router.



  • @frodooftheshire said in Comcast gateway LAN/router LAN conflict?:

    @travisdh1 yes. I can ping the Comcast's gateway IP and the usable IP configured on the router.

    From outside your local network? You shouldn't be able to reach the 10.1.10.X subnet as it's a private IP range.



  • @travisdh1 The usable WAN ip address that's configured on the WAN side of the router.



  • Just to clarify, here in Oregon when you pay for a static IP address from Comcast (either a single or in a block of 5) you have the gateway's public IP address, then the usable public static IP address that you can assign to your router.



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    Just imagine this, but with the LAN subnet on the Comcast gateway to be idential to the LAN side of the linksys router.



  • Don't get hung up on the static address. I think he was assuming you had DHCP. You either need to change the subnet on the Comcast gateway or the Luxul router.


  • Service Provider

    @frodooftheshire said in Comcast gateway LAN/router LAN conflict?:

    @JaredBusch They pay for a dedicated static IP from Comcast. What would you call it if not a static IP?

    A fixed IP.

    It is of course possible that Comcast is using a a true static IP assignment. But it is unlikely.

    If it was a true static, then your comcast modem will have another public WAN IP and the /30 you have is routed behind that.


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