[gPXE] Strange ARP problem with gpxe 1.0.0+

[Ben Derstine]

Hi,  I'm using gpxe 1.0.0+ and it's not working in certain cases where
it tries to ARP for the default gateway I configured for it via a
script.  After a lot of head scratching I finalized sniffed the traffic
using Wireshark to see exactly what it was doing when it didn't work
versus what it was doing when it did work.   I've included the two ARP
requests below.   It works when I plug the computer that I'm using gpxe
for into a little Netgear switch which then connects to a Cisco 2960.
When I plug it directly into the 2960 it doesn't work.   The ARP request
packets from gpxe look slightly different between these two scenarios
(top one works):

 

No.     Time        Source                Destination           Protocol
Info

      1 0.000000    Dell_35:67:ed         Broadcast             ARP
Who has 172.28.113.1?  Tell 172.28.113.203

 

Frame 1 (60 bytes on wire, 60 bytes captured)

    Arrival Time: May 17, 2010 11:13:17.736812000

    [Time delta from previous captured frame: 0.000000000 seconds]

    [Time delta from previous displayed frame: 0.000000000 seconds]

    [Time since reference or first frame: 0.000000000 seconds]

    Frame Number: 1

    Frame Length: 60 bytes

    Capture Length: 60 bytes

    [Frame is marked: False]

    [Protocols in frame: eth:arp]

    [Coloring Rule Name: ARP]

    [Coloring Rule String: arp]

Ethernet II, Src: Dell_35:67:ed (00:24:e8:35:67:ed), Dst: Broadcast
(ff:ff:ff:ff:ff:ff)

    Destination: Broadcast (ff:ff:ff:ff:ff:ff)

    Source: Dell_35:67:ed (00:24:e8:35:67:ed)

    Type: ARP (0x0806)

    Trailer: 000000000000000000000000000000000000

Address Resolution Protocol (request)

    Hardware type: Ethernet (0x0001)

    Protocol type: IP (0x0800)

    Hardware size: 6

    Protocol size: 4

    Opcode: request (0x0001)

    Sender MAC address: Dell_35:67:ed (00:24:e8:35:67:ed)

    Sender IP address: 172.28.113.203 (172.28.113.203)

    Target MAC address: 00:00:00_00:00:00 (00:00:00:00:00:00)

    Target IP address: 172.28.113.1 (172.28.113.1)

 

This one doesn't work:

 

No.     Time        Source                Destination           Protocol
Info

      1 0.000000    Dell_35:67:ed         Broadcast             ARP
Who has 172.28.113.1?  Tell 172.28.113.203

 

Frame 1 (60 bytes on wire, 60 bytes captured)

    Arrival Time: May 17, 2010 11:25:38.286573000

    [Time delta from previous captured frame: 0.000000000 seconds]

    [Time delta from previous displayed frame: 0.000000000 seconds]

    [Time since reference or first frame: 0.000000000 seconds]

    Frame Number: 1

    Frame Length: 60 bytes

    Capture Length: 60 bytes

    [Frame is marked: False]

    [Protocols in frame: eth:arp]

    [Coloring Rule Name: ARP]

    [Coloring Rule String: arp]

Ethernet II, Src: Dell_35:67:ed (00:24:e8:35:67:ed), Dst: Broadcast
(ff:ff:ff:ff:ff:ff)

    Destination: Broadcast (ff:ff:ff:ff:ff:ff)

        Address: Broadcast (ff:ff:ff:ff:ff:ff)

        .... ...1 .... .... .... .... = IG bit: Group address
(multicast/broadcast)

        .... ..1. .... .... .... .... = LG bit: Locally administered
address (this is NOT the factory default)

    Source: Dell_35:67:ed (00:24:e8:35:67:ed)

        Address: Dell_35:67:ed (00:24:e8:35:67:ed)

        .... ...0 .... .... .... .... = IG bit: Individual address
(unicast)

        .... ..0. .... .... .... .... = LG bit: Globally unique address
(factory default)

    Type: ARP (0x0806)

    Trailer: 000000000000000000000000000000000000 

Address Resolution Protocol (request)

    Hardware type: Ethernet (0x0001)

    Protocol type: IP (0x0800)

    Hardware size: 6

    Protocol size: 4

    Opcode: request (0x0001)

    Sender MAC address: Dell_35:67:ed (00:24:e8:35:67:ed)

    Sender IP address: 172.28.113.203 (172.28.113.203)

    Target MAC address: 00:00:00_00:00:00 (00:00:00:00:00:00)

    Target IP address: 172.28.113.1 (172.28.113.1)

 

 

Note that the different between the two is in the Ethernet II field with
the IG/LG bits.   Does this make sense to anyone?

 

Ben

 

Benjamin Derstine

Systems Administrator

Pennsylvania State University 
Division of Student Affairs 
Information Technology 
222 Boucke Building 
University Park, PA 16802 

Phone:  814-863-9844

Fax:  814-863-0299

bld17 at sa.psu.edu <mailto:bld17 at sa.psu.edu> 
http://www.sa.psu.edu <http://www.sa.psu.edu/>   

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://etherboot.org/pipermail/gpxe/attachments/20100517/bb0dc40b/attachment.html