PXE boot through router

Answered Question
Jun 18th, 2010

Hi,

We have two LAN in my enterprise.One LAN is for server and other is for users.Cisco Router act as a DHCP server for the user LAN.Now we are planning for PXE boot for user LAN.My PXE boot server is located in the server LAN.What are the changes needs to be done at the router to make this work.

I have this problem too.
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Correct Answer by Giuseppe Larosa about 3 years 10 months ago

Hello Uthayaman,

on client vlan facing router interface you need the command

ip helper-address pxe-server-address

this command converts unroutable packets with broadcast destination to routable packets with unicast destination = pxe-server-address

one field in the packet is updated with the router's IP address of client facing interface so that DHCP server can pick up an IP address from correct address pool

to be noted LAN switch ports should be configured with spanning-tree portfast otherwise PXE boot can fail for the STP standard timers (up to 30 seconds before making the port operational)

Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Fri, 06/18/2010 - 10:15

Hello Uthayaman,

on client vlan facing router interface you need the command

ip helper-address pxe-server-address

this command converts unroutable packets with broadcast destination to routable packets with unicast destination = pxe-server-address

one field in the packet is updated with the router's IP address of client facing interface so that DHCP server can pick up an IP address from correct address pool

to be noted LAN switch ports should be configured with spanning-tree portfast otherwise PXE boot can fail for the STP standard timers (up to 30 seconds before making the port operational)

Hope to help

Giuseppe

uthayaman Fri, 06/25/2010 - 15:10

Thx...

I have done this.Now my clients are not getiing IP from the DHCP server.We have a MPLS VPN(Provided by a service provider) between the client and server.Whether this will block DHCP boot request packet from client to server.

I can arble to see the gaddress getting changed in the clients gateway(Router A) and forwaded to DHCP server.But this is not reaching the router B.

Client<------>RouterA------MPLS-----------RouterB<-------->DHCP server


Do i need to take it up with my service provider.Because i never faced any such issue with MPLS link till now.

Giuseppe Larosa Sun, 06/27/2010 - 12:02

Hello Uthayaman,

thanks for your kind remarks

>> I can arble to see the gaddress getting changed in the clients gateway(Router A) and forwaded to DHCP server.But this is not reaching the router B.

but can you ping from RA's lan ip address to RB's lan ip address ?

in any case I agree that you need to involve the SP

Hope to help

Giuseppe

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Posted June 18, 2010 at 8:55 AM
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