PXE boot via Cisco router

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Sep 29th, 2010
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We have a need to netboot a PC with Linux via a Cisco router (I.E. PXEboot).

We have copied the PXE linux.cfg files to the Cisco router's flash, (Cisco 2821, IOS Advanced Security 15-1.2-T1).

We have setup the router as a TFTP server with defaulted path as tftp-server flash:tftpboot

From the pc's CMOS, we selected PXE boot.


With "debug ip packet detail", we can see the DHCP request from the PC.

We cannot however, get the router to download the Linux files to the PC.


Manually we tried:

c:\ tftp 10.0.0.1 get default - no go.


ANYONE have an idea????

Thanks

Frank

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Ashley Georgeson Wed, 09/29/2010 - 14:29
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Hi Frank,


Do you need to do this from the router or do you have a server available?


The reason I ask is you could try and use ip helper to forward pxe to the server.


Anyway, if you need to use the router, is it configured for dhcp?  And does it have an option 150 configured for tftp?


It is strange that you can not connect to it via tftp though - are there any access-lists on the routed interface?


I would set up a tftp daemon on a test pc, e.g. tftpd32, and try a tftp copy to/from the router to confirm the protocol work okay.  Then we know it is just a matter of configuration or implementation, not underlying transport.


Regards, Ash.

fsebera Thu, 09/30/2010 - 18:19
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Hi Ash,

Thanks for the assistance.

The laptop is directly connected to the Cisco 2821 routers g0/0 interface.

The router is configured to be a DHCP server with the Cisco 2821 router IP address on g0/0 set in the DHCP configuration to be the default router. The router’s IP address is excluded from DHCP. (10.0.0.30)


If the laptop’s bios is set to PXE boot, it seems to receive an IP address from the router I.E. 10.0.0.1– verified by statically assigning another pc IP address 10.0.0.1– the 2nd pc receives an error of IP address conflict. Then set the second pc to obtain its’ IP address via DHCP, and while running debug ip packet detail on the router, I see the router running through the DHCP assignment process and finally assigns the 2nd pc 10.0.0.2.


So needless to say, I believe the DHCP setup is functioning correctly.


The problem we have at this point is nailing down the TFTP-server function running on the Cisco 2821 router.


We were able to create the directory tree on the Cisco 2821 routers flash and then copy the correct files into each directory within flash.


Using WinXP DOS prompt, tftp does not seem to function.

With debug ip packet detail running on the router and Wireshark running on the PC, we run from a DOS window c:\tftp 10.0.0.1 GET \default. No matter how we specify the path, end result is an error of some kind.

We watch debug and wireshark display the communications of the PC and router talking, but cannot seem to get the requested file.


Perhaps WinXP tftp server is flawed.

If we load TFTP32 and attempt to send and/or receive a file from flash, works fine.


The router tftp config is as:

tftp-server flash:/tftpboot/dsl/pxeboot.cfg

The actual files name is "default" and is found on the Cisco 2821 flash:/tftpboot/dsl/pxeboot.cfg directory.


No ACLs on the Cisco router and the router is pretty much right out of the box.

Firewall is disabled on both PCs.

Ping to/from the PC/router works fine.


Thanks again

Frank

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