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We have a big old Dell running RedHat, which does nothing (any more) but |
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serve DHCP for a number of labs around our campus. We thought it would |
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be an ideal candidate for replacement with a home-rolled GNAP machine |
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using dnsmasq's DHCP service. It seemed to work well in testing, but |
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when we dropped in the replacement system we found that machines on |
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remote VLANs could no longer get addresses. |
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|
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The campus network runs on Cisco switches, controlled by another group. |
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I'm pretty much Cisco-ignorant myself, but my undertanding is that the |
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VLANs which serve our DHCP clients have been configured to propagate |
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DHCP requests beyond the local segment and on to our centrally-located |
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DHCP server, and this works fine with the old machine. |
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|
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A little tcpdumping shows some differences between the old (RedHat) box |
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and the new (GNAP) system. In this example, "msfc-ri-v17.uchicago.edu" |
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is the router which serves our DHCP client; "dell-test-03.uchicago.edu" |
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is the DHCP client; and "bonzai.uchicago.edu" houses the DHCP server. |
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tcpdump is running on bonzai: |
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|
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14:42:27.985373 msfc-ri-v17.uchicago.edu.bootps > bonzai.uchicago.edu.bootps: (request) hops:1 xid:0x20dcf2e1 secs:4 flags:0x8000 G:msfc-ri-v17.uchicago.edu ether 0:f:1f:dc:f2:e1 [|bootp] |
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14:42:27.986066 bonzai.uchicago.edu.bootps > msfc-ri-v17.uchicago.edu.bootps: (reply) hops:1 xid:0x20dcf2e1 secs:4 flags:0x8000 Y:dell-test-03.uchicago.edu S:bonzai.uchicago.edu G:msfc-ri-v17.uchicago.edu ether 0:f:1f:dc:f2:e1 [|bootp] (DF) |
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Now here's an example of the same case, except that the hardware acting |
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as bonzai.uchicago.edu is now our GNAP machine: |
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|
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01:06:27.601181 IP msfc-ri-v17.uchicago.edu.bootps > bonzai.uchicago.edu.bootps: BOOTP/DHCP, Request [|bootp] |
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The GNAP box doesn't issue a response, apparently because it can't see |
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that the request is coming from one of its listed DHCP clients. |
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So, does anybody know what might be going on here? I don't think that |
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dnsmasq is (necessarily) the culprit, since tcpdump shows more |
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information in the case of the packets dumped on the RedHat machine. Is |
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this a difference, maybe, in the uclibc network handling? Do I need to |
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tweak my kernel? Am I just crazy? |
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|
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Thanks for any thoughts. |
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|
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--Michael |
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-- |
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