switch over failure of WAN link

Unanswered Question
Aug 16th, 2009

I am working in company and they want to implement below thing, need ur help?in our branch there is one router and one unmanagable D link switch..OK...Router is connected to switch and switch is connected to Pc. and PC's default gateway is routers interface that is connecte to switch....NOW we have two WAN link one is coming from Tulip service provider and terminated on the router....and the other VSAT link is directly terminated to the LAN D link switch..so the problem is when my tulip link goes down then we have to change the gateway of all PC to divert the traffic from VSAT link. so I need a configuration on router so that we can switch over to

VSAT without chaning gateway of devices.



see attachement

I have this problem too.
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Mohamed Sobair Sun, 08/16/2009 - 06:05


The only way I could think of is to change the switch to act as layer-3 switch.

You would set the PCs default GW to the SVI interface on the switch. then the switch could have HSRP , VRRP between the router , vasat router and the switch. Or the switch itself could have 2 routes pointing to the VSAT and the router as its next-hop with one be the prefered path.

This way, the switch would detect a failure on the upstream next-hop and would route the traffic across the desired path. therfore.



shaikh.irfan Sun, 08/16/2009 - 07:26

but the Vsat link is not terminated on router its directly terminated on switch then how is HSRP possible.

Mohamed Sobair Sun, 08/16/2009 - 09:35


Here are the options:

1- Having the VSAT link & the router on one segment with the switch SVI and do HSRP , VRRP. PCS default GW is another L3 SVI on the Switch.

2- Having the VSAT link & the router terminated on layer-3 port each on the Switch with 2 default routes pointing to both nexthops with one prefered (By setting Higher AD value on the second one).

Hope you get my point,


shaikh.irfan Mon, 08/17/2009 - 08:16


I didn't get ur firsr point, my router is connected to switch and vsat is also connected to switch. so where should i do HSRP.. between my L3 switch and router? Can u give me details with command...

netbeginner Wed, 08/19/2009 - 09:07

Hello Sheikh,

To achieve the desire you can also go Serial cable for VSAT , which you can connect to Routers serial interface port if you have two serial interfaces on router, after which you can configure higher metric route toward Vsat serial interface and primary towards ISP network.This cable is like normal V.35 cable and can be extended from VSAT IDU to Serial interface called V.24 .......As for as your LAN IPs are concerned you can configure same LAN IP pools for ISP and Vsat connectivity (If you don't have any limitations).


shaikh.irfan Thu, 08/20/2009 - 05:26

Can i use the same LAN subnet ip for serial interface where i connect Vsat IDU. and suppose if don't have then can i use WIC card....and is there any possiblity to use fast ethernet port. if yes then can i use the same subnet ip becaus my vsat ip is the ip from LAN subnet range.



netbeginner Thu, 08/20/2009 - 09:12

===> can i use WIC card

1) Yes , you can use WIC serial card with Vsat IDU.

==> Is there any possiblity to use fast ethernet port

2) Did you mean for ..use of Fast ethernet port as VSAT WAN connectivity.

If yes, then it may also possible..but again in this case you need serial to ethernet converter..Hence better to go with WIC / Serial interface.

==>If yes then can i use the same subnet ip becaus my vsat ip is the ip from LAN subnet range.

3) First i need to confirm if u using same LAN pool for Tulip & Vsat both...?


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