Connecting a Satellite Modem

Unanswered Question
Mar 19th, 2010


First of all, I want to apologize if my questions are giong to be stupid.

Here is my problem :

I have a open network satellite modem which needs to be fed data through its synchronous serial interface.

The data is a video stream generated on a laptop.

I have a old 2650XM cisco router with a WIC1T installed, and a netgear fast etherent switch.

I was wondering if I could plug both my laptop and the cisco router to the switch, the modem to the WIC 1T interface, and use the router as an interface between my modem and my laptop.

In my head I was picturing sending UDP packets to the routers, which then will encapsulate with PPP sync protocol and send it over the sync serial link to the modem, which then transmit whatever it receives.

Do you think I can achieve that with the components I have ? It also need to be half duplex.

Well hope you can help me.

thanks !

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Giuseppe Larosa Fri, 03/19/2010 - 05:59

Hello Martin,

your understanding is correct but a similar setup will be needed on the other site

PC1 --- switch -- router--- serial ---- satellite -----router ---- switch ---- PC2

PC1 and PC2 will be in a different IP subnet

unless you want to try to do bridging over serial but it is not recommended

Hope to help


mvivies2010 Fri, 03/19/2010 - 06:37


Thanks for the answer.

Indeed there will be a similar system on the other side, here is the complete system :

PC1 - switch - cisco 2650xm - Satellite modem - Satellite Link - Satellite modem - Cisco router - switch - PC2

So it is similar to what you suggested.

So now that I know that i was not completely off subject, I have more questions :

How do I configure the WIC interface:  what Ip address should I give it, and what subnet mask : or does it depend on PC2 settings?

Should I just create a Ip route on the router that just takes every packet received on the ethernet port and sends it to the serial interface ?

And another that takes packets received on the serial interface and send them to the IP adress of PC1

I am asking this, because in a first step, I would want to use the satellite modem loopback function to see that I can actually send the packets to the modem ( I don't have access yet to the satellite link, which is an expensive ressource).

Sorry I am really new at this.

Thanks again

Giuseppe Larosa Fri, 03/19/2010 - 09:54

Hello Martin,

a routed solution is recommended

PC1 will be in one subnet example together with R1 ethernet 0

A different IP subnet is used on serial link and can be chosen for example R1:serial ---- R2:serial

PC2 and R2 lan in another subnet like

R1 and R2 must know about what IP subnet is behind the other device. This can be done with static routes or with a routing protocol.

I recommend the use of a dynamic routing protocol to detect when satellite link is really alive.

example with EIGRP

! on  R1:

router eigrp 100



no auto-summary

! on R2:

router eigrp 100



no auto-summary

Hope to help


mvivies2010 Mon, 03/22/2010 - 01:24

Thanks so much giuslar,

I have a clearer view on what I need to do.

From your answer I am guessing that if the other end of the system is not set up, I can't use a dynamic route, but by using a static route I can use the router to send data to the modem and test that this works. Am I right ?

Do you think that if i use the modem loopback function, I can send and receive the stream on the same computer, by just using a static route from the interface, to the IP address of the PC1 ?

Thanks so much for your help !

Giuseppe Larosa Mon, 03/22/2010 - 01:31

Hello Martin,

>> Do you think that if i use the modem loopback function, I can send and  receive the stream on the same computer, by just using a static route  from the interface, to the IP address of the PC1 ?

No, this is not possible if the destination ip address is that of PC1 the packet will not be forwarded to the serial link/satellite modem.

To perform a test both sites have to be configured.

Hope to help


mvivies2010 Mon, 03/22/2010 - 01:54

Thanks so much for such a quick answer.

I wasn't thinking previously, your answer makes perfect sense and I realize now that I won't be able to test my side of the conenxion unless I have the whole system set up, which is a bummer but i'll survive.
Thanks so much for your help.

mvivies2010 Thu, 07/08/2010 - 03:37

Hello Giuseppe,

Sorry to repost on such a old thread,

But at the time I asked for your advice I didn't have all the equipment so I could not test it.

I received everything but I am encountering problems.

First of all just to go step by step, I tried the config you said but instead of using the serial interface. I configured the second Ethernet interface, and connected the two cisco routers with a crossover cable.

PC1 --- Switch ---- Routeur 1------Ethernet Crossover Cable ---- Routeur 2 ---Switch--- PC2

And I configured the other equipment as you told me.

R1 Ethernet 0  ip address

R1 Ethernet 1 ip address

R2 Ethernet 0  ip address

R2 Ethernet 1 ip address

PC1 ip address

PC2 ip address

I can ping from R1 and from R2

But I can't ping from R1 or from R2.

I can also ping from PC1 same for PC2 and R2.

I don't understand why this is not working, sorry if this question seems stupid.



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