Dual DHCP default-router work

[ekhoo]

Does anyone know how the multiple default-routers work? According to Cisco we can specify up to eight addresses in one command line.

eg:

default-router address1..address2...address8

I have tested on my lab with WinXP. I can get more then one default-gateway from the router. However, the PC only use the fist gateway and never failover to second or third gateway..

regards,

sean

[andrew.butterworth · Accepted solution]

I seem to remember something on Microsoft's website about this ages ago (TCP/IP Implementation details for Windows NT 4.0?). Apparently its TCP based.... What happens is if the 1st gateway is no longer available the TCP stack will detect this and switch over to the 2nd gateway. This only works if you have a TCP application that is attempting to send traffic; simply pinging a remote device won't work:

http://www.microsoft.com/technet/community/columns/cableguy/cg1105.mspx

http://www.winguides.com/registry/display.php/886/

http://www.microsoft.com/technet/community/columns/cableguy/cg0903.mspx

HTH

Andy

[ekhoo]

Thanks Andy. Appreciate your input.

i am preparing my lab exam at the moments.. and trying to understand the DHCP inside out..

Do you think dual default-router is the best solution to ensure full connectivity? Would VRRP and HSRP the better solution?

regards,

sean

[mahmoodmkl]

Hi

I would prefer HSRP and VRRP then using two routers as gateways.the clients need to know only abt one gateway address.

Thanks

Mahmood

[andrew.butterworth]

Mahmood - yes that would be the preferred solution. HSRP does not require any configuration on the clients and is completely transparent.

Andy