Comments (5)
hugelgupf
commented on June 12, 2024
1
I'd think this is your server not replying with the correct hostname. Do you suspect that the DHCP client is setting that hostname? Have you looked at what the packet looks like on the wire (tcpdump)?
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andrewrynhard
commented on June 12, 2024
@hugelgupf here is output from sudo dhcpdump -i enp5s0 using the above code:
TIME: 2019-02-24 18:41:50.470
IP: 192.168.124.128 (50:46:5d:8a:e7:9f) > 255.255.255.255 (ff:ff:ff:ff:ff:ff)
OP: 1 (BOOTPREQUEST)
HTYPE: 1 (Ethernet)
HLEN: 6
HOPS: 0
XID: 3e6f933a
SECS: 0
FLAGS: 7f80
CIADDR: 0.0.0.0
YIADDR: 0.0.0.0
SIADDR: 0.0.0.0
GIADDR: 0.0.0.0
CHADDR: 50:46:5d:8a:e7:9f:00:00:00:00:00:00:00:00:00:00
SNAME: .
FNAME: .
OPTION: 53 ( 1) DHCP message type 1 (DHCPDISCOVER)
OPTION: 55 ( 5) Parameter Request List 1 (Subnet mask)
3 (Routers)
15 (Domainname)
6 (DNS server)
12 (Host name)
---------------------------------------------------------------------------
TIME: 2019-02-24 18:41:50.470
IP: 192.168.124.1 (7a:8a:20:f6:87:46) > 255.255.255.255 (ff:ff:ff:ff:ff:ff)
OP: 2 (BOOTPREPLY)
HTYPE: 1 (Ethernet)
HLEN: 6
HOPS: 0
XID: 3e6f933a
SECS: 0
FLAGS: 7f80
CIADDR: 0.0.0.0
YIADDR: 192.168.124.128
SIADDR: 192.168.124.1
GIADDR: 0.0.0.0
CHADDR: 50:46:5d:8a:e7:9f:00:00:00:00:00:00:00:00:00:00
SNAME: .
FNAME: .
OPTION: 53 ( 1) DHCP message type 2 (DHCPOFFER)
OPTION: 54 ( 4) Server identifier 192.168.124.1
OPTION: 51 ( 4) IP address leasetime 43200 (12h)
OPTION: 58 ( 4) T1 21600 (6h)
OPTION: 59 ( 4) T2 37800 (10h30m)
OPTION: 1 ( 4) Subnet mask 255.255.255.0
OPTION: 28 ( 4) Broadcast address 192.168.124.255
OPTION: 26 ( 2) Interface MTU 1500
OPTION: 3 ( 4) Routers 192.168.124.1
OPTION: 6 ( 4) DNS server 192.168.124.1
---------------------------------------------------------------------------
I don't see OPTION: 12 ( 4) Host name dkr1 in the reply as I do with dhclient:
TIME: 2019-02-24 18:42:28.123
IP: 0.0.0.0 (50:46:5d:8a:e7:9f) > 255.255.255.255 (ff:ff:ff:ff:ff:ff)
OP: 1 (BOOTPREQUEST)
HTYPE: 1 (Ethernet)
HLEN: 6
HOPS: 0
XID: 6c42dc09
SECS: 0
FLAGS: 0
CIADDR: 0.0.0.0
YIADDR: 0.0.0.0
SIADDR: 0.0.0.0
GIADDR: 0.0.0.0
CHADDR: 50:46:5d:8a:e7:9f:00:00:00:00:00:00:00:00:00:00
SNAME: .
FNAME: .
OPTION: 53 ( 1) DHCP message type 3 (DHCPREQUEST)
OPTION: 50 ( 4) Request IP address 192.168.124.128
OPTION: 12 ( 4) Host name dkr1
OPTION: 55 ( 13) Parameter Request List 1 (Subnet mask)
28 (Broadcast address)
2 (Time offset)
3 (Routers)
15 (Domainname)
6 (DNS server)
119 (Domain Search)
12 (Host name)
44 (NetBIOS name server)
47 (NetBIOS scope)
26 (Interface MTU)
121 (Classless Static Route)
42 (NTP servers)
---------------------------------------------------------------------------
TIME: 2019-02-24 18:42:28.124
IP: 192.168.124.1 (7a:8a:20:f6:87:46) > 192.168.124.100 (1a:56:47:82:13:a0)
OP: 2 (BOOTPREPLY)
HTYPE: 1 (Ethernet)
HLEN: 6
HOPS: 0
XID: ff5c4454
SECS: 0
FLAGS: 0
CIADDR: 0.0.0.0
YIADDR: 192.168.124.100
SIADDR: 192.168.124.1
GIADDR: 0.0.0.0
CHADDR: 1a:56:47:82:13:a0:00:00:00:00:00:00:00:00:00:00
SNAME: .
FNAME: .
OPTION: 53 ( 1) DHCP message type 5 (DHCPACK)
OPTION: 54 ( 4) Server identifier 192.168.124.1
OPTION: 51 ( 4) IP address leasetime 43200 (12h)
OPTION: 58 ( 4) T1 21600 (6h)
OPTION: 59 ( 4) T2 37800 (10h30m)
OPTION: 1 ( 4) Subnet mask 255.255.255.0
OPTION: 12 ( 4) Host name dkr1
OPTION: 28 ( 4) Broadcast address 192.168.124.255
OPTION: 26 ( 2) Interface MTU 1500
OPTION: 3 ( 4) Routers 192.168.124.1
OPTION: 6 ( 4) DNS server 192.168.124.1
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hugelgupf
commented on June 12, 2024
Those are different hosts with different hostnames. I'd really like to see what tcpdump on the server looks like, if you can swing it, to see what bytes it is putting on the wire.
The parsing code for HostName() is fairly simple, and "localhost" is as far as I can tell not even a string I can find in the dhcpv4 library. Next, I'd have three points of "where to look":
-
while the server is supposed to return the same options for both the offer and the ack, you're looking at the Offer packet while dhclient looks at the Ack. I'm curious if the Ack packet has a different hostname. (Note that #250 improves the API for Exchange and just returns the correct offer and ack packets.)
-
if tcpdump at the server or somewhere in the middle indicates that "localhost" was sent; I'd suspect either server misconfig (though you show it seems to work for others, so less likely) or that we screwed up how the client is identified by the server (I assume Mac address?). I'd suspect the latter?
-
in client4, it'd be interesting to see what the payload variable in SendReceive contains right before dhcpv4.FromBytes is called. This'd be a more complicated way of finding out what was actually on the wire.
My money is on "we screwed up the identifier," but it's still weird.
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andrewrynhard
commented on June 12, 2024
@hugelgupf Thanks. I seemed to have borked my KVM setup, VMs timing out on DHCP now :D. As soon as I get that figured out I will get back to you!
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pmazzini
commented on June 12, 2024
Shall I close this?
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