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Old 05-15-2012, 01:12 PM
Panayiotis Karabassis
 
Default strangeness with dhcp relay server

Hiya,

I had posted a while back about this problem, and it seems critical
information was under my nose.

I am running my own dhcpd server on my Debian box. Often a client would
send DISCOVER packets, but receive no reply. The information comes from
wireshark running on the server machine, and I attach the relevant packets.

My network is:

DHCP server (wheezy)
<--(wifi)-->
Linksys X3000 router acting as a DHCP relay
<--(wifi)-->
Linksys RE1000 repeater
<--(wifi)-->
client machine

As you can see the DHCP server receives the DISCOVER message and replies
with an OFFER message to the router (relay). And then the router sends
the OFFER back to the server instead of the client!

Linksys is a good company as far as I know, so this must be my fault.
Does anyone have any ideas?

Best regards and thanks,
Panayiotis
No. Time Source Destination Protocol Length Info
367 6.833302 192.168.1.1 192.168.1.10 DHCP 342 DHCP Discover - Transaction ID 0xdf8b6c3b

Frame 367: 342 bytes on wire (2736 bits), 342 bytes captured (2736 bits)
Arrival Time: May 15, 2012 15:51:36.394352000 EEST
Epoch Time: 1337086296.394352000 seconds
[Time delta from previous captured frame: 0.010130000 seconds]
[Time delta from previous displayed frame: 0.000000000 seconds]
[Time since reference or first frame: 6.833302000 seconds]
Frame Number: 367
Frame Length: 342 bytes (2736 bits)
Capture Length: 342 bytes (2736 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: eth:ip:udp:bootp]
[Coloring Rule Name: UDP]
[Coloring Rule String: udp]
Ethernet II, Src: Cisco-Li_d5:7b:76 (98:fc:11:d5:7b:76), Dst: Giga-Byt_3b:c3:e9 (00:16:e6:3b:c3:e9)
Destination: Giga-Byt_3b:c3:e9 (00:16:e6:3b:c3:e9)
Address: Giga-Byt_3b:c3:e9 (00:16:e6:3b:c3:e9)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Source: Cisco-Li_d5:7b:76 (98:fc:11:d5:7b:76)
Address: Cisco-Li_d5:7b:76 (98:fc:11:d5:7b:76)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Type: IP (0x0800)
Internet Protocol Version 4, Src: 192.168.1.1 (192.168.1.1), Dst: 192.168.1.10 (192.168.1.10)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))
0000 00.. = Differentiated Services Codepoint: Default (0x00)
.... ..00 = Explicit Congestion Notification: Not-ECT (Not ECN-Capable Transport) (0x00)
Total Length: 328
Identification: 0x0000 (0)
Flags: 0x02 (Don't Fragment)
0... .... = Reserved bit: Not set
.1.. .... = Don't fragment: Set
..0. .... = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: UDP (17)
Header checksum: 0xb649 [correct]
[Good: True]
[Bad: False]
Source: 192.168.1.1 (192.168.1.1)
Destination: 192.168.1.10 (192.168.1.10)
User Datagram Protocol, Src Port: bootps (67), Dst Port: bootps (67)
Source port: bootps (67)
Destination port: bootps (67)
Length: 308
Checksum: 0x54a7 [validation disabled]
[Good Checksum: False]
[Bad Checksum: False]
Bootstrap Protocol
Message type: Boot Request (1)
Hardware type: Ethernet
Hardware address length: 6
Hops: 1
Transaction ID: 0xdf8b6c3b
Seconds elapsed: 18
Bootp flags: 0x0000 (Unicast)
0... .... .... .... = Broadcast flag: Unicast
.000 0000 0000 0000 = Reserved flags: 0x0000
Client IP address: 0.0.0.0 (0.0.0.0)
Your (client) IP address: 0.0.0.0 (0.0.0.0)
Next server IP address: 0.0.0.0 (0.0.0.0)
Relay agent IP address: 192.168.1.1 (192.168.1.1)
Client MAC address: 5a:6d:8f:a7:9a:56 (5a:6d:8f:a7:9a:56)
Client hardware address padding: 00000000000000000000
Server host name not given
Boot file name not given
Magic cookie: DHCP
Option: (t=53,l=1) DHCP Message Type = DHCP Discover
Option: (53) DHCP Message Type
Length: 1
Value: 01
Option: (t=50,l=4) Requested IP Address = 192.168.1.12
Option: (50) Requested IP Address
Length: 4
Value: c0a8010c
Option: (t=55,l=13) Parameter Request List
Option: (55) Parameter Request List
Length: 13
Value: 011c02030f06770c2c2f1a792a
1 = Subnet Mask
28 = Broadcast Address
2 = Time Offset
3 = Router
15 = Domain Name
6 = Domain Name Server
119 = Domain Search [TODO:RFC3397]
12 = Host Name
44 = NetBIOS over TCP/IP Name Server
47 = NetBIOS over TCP/IP Scope
26 = Interface MTU
121 = Classless Static Route
42 = Network Time Protocol Servers
End Option
Padding

0000 00 16 e6 3b c3 e9 98 fc 11 d5 7b 76 08 00 45 00 ...;......{v..E.
0010 01 48 00 00 40 00 40 11 b6 49 c0 a8 01 01 c0 a8 .H..@.@..I......
0020 01 0a 00 43 00 43 01 34 54 a7 01 01 06 01 df 8b ...C.C.4T.......
0030 6c 3b 00 12 00 00 00 00 00 00 00 00 00 00 00 00 l;..............
0040 00 00 c0 a8 01 01 5a 6d 8f a7 9a 56 00 00 00 00 ......Zm...V....
0050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0080 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0090 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00e0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0100 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0110 00 00 00 00 00 00 63 82 53 63 35 01 01 32 04 c0 ......c.Sc5..2..
0120 a8 01 0c 37 0d 01 1c 02 03 0f 06 77 0c 2c 2f 1a ...7.......w.,/.
0130 79 2a ff 00 00 00 00 00 00 00 00 00 00 00 00 00 y*..............
0140 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0150 00 00 00 00 00 00 ......
No. Time Source Destination Protocol Length Info
368 6.833568 192.168.1.10 192.168.1.1 DHCP 354 DHCP Offer - Transaction ID 0xdf8b6c3b

Frame 368: 354 bytes on wire (2832 bits), 354 bytes captured (2832 bits)
Arrival Time: May 15, 2012 15:51:36.394618000 EEST
Epoch Time: 1337086296.394618000 seconds
[Time delta from previous captured frame: 0.000266000 seconds]
[Time delta from previous displayed frame: 0.000266000 seconds]
[Time since reference or first frame: 6.833568000 seconds]
Frame Number: 368
Frame Length: 354 bytes (2832 bits)
Capture Length: 354 bytes (2832 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: eth:ip:udp:bootp]
[Coloring Rule Name: UDP]
[Coloring Rule String: udp]
Ethernet II, Src: Giga-Byt_3b:c3:e9 (00:16:e6:3b:c3:e9), Dst: Cisco-Li_d5:7b:76 (98:fc:11:d5:7b:76)
Destination: Cisco-Li_d5:7b:76 (98:fc:11:d5:7b:76)
Address: Cisco-Li_d5:7b:76 (98:fc:11:d5:7b:76)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Source: Giga-Byt_3b:c3:e9 (00:16:e6:3b:c3:e9)
Address: Giga-Byt_3b:c3:e9 (00:16:e6:3b:c3:e9)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Type: IP (0x0800)
Internet Protocol Version 4, Src: 192.168.1.10 (192.168.1.10), Dst: 192.168.1.1 (192.168.1.1)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))
0000 00.. = Differentiated Services Codepoint: Default (0x00)
.... ..00 = Explicit Congestion Notification: Not-ECT (Not ECN-Capable Transport) (0x00)
Total Length: 340
Identification: 0x0000 (0)
Flags: 0x02 (Don't Fragment)
0... .... = Reserved bit: Not set
.1.. .... = Don't fragment: Set
..0. .... = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: UDP (17)
Header checksum: 0xb63d [correct]
[Good: True]
[Bad: False]
Source: 192.168.1.10 (192.168.1.10)
Destination: 192.168.1.1 (192.168.1.1)
User Datagram Protocol, Src Port: bootps (67), Dst Port: bootps (67)
Source port: bootps (67)
Destination port: bootps (67)
Length: 320
Checksum: 0xec0a [validation disabled]
[Good Checksum: False]
[Bad Checksum: False]
Bootstrap Protocol
Message type: Boot Reply (2)
Hardware type: Ethernet
Hardware address length: 6
Hops: 1
Transaction ID: 0xdf8b6c3b
Seconds elapsed: 18
Bootp flags: 0x0000 (Unicast)
0... .... .... .... = Broadcast flag: Unicast
.000 0000 0000 0000 = Reserved flags: 0x0000
Client IP address: 0.0.0.0 (0.0.0.0)
Your (client) IP address: 192.168.1.12 (192.168.1.12)
Next server IP address: 0.0.0.0 (0.0.0.0)
Relay agent IP address: 192.168.1.1 (192.168.1.1)
Client MAC address: 5a:6d:8f:a7:9a:56 (5a:6d:8f:a7:9a:56)
Client hardware address padding: 00000000000000000000
Server host name not given
Boot file name not given
Magic cookie: DHCP
Option: (t=53,l=1) DHCP Message Type = DHCP Offer
Option: (53) DHCP Message Type
Length: 1
Value: 02
Option: (t=54,l=4) DHCP Server Identifier = 192.168.1.10
Option: (54) DHCP Server Identifier
Length: 4
Value: c0a8010a
Option: (t=51,l=4) IP Address Lease Time = 12 hours
Option: (51) IP Address Lease Time
Length: 4
Value: 0000a8c0
Option: (t=1,l=4) Subnet Mask = 255.255.255.0
Option: (1) Subnet Mask
Length: 4
Value: ffffff00
Option: (t=28,l=4) Broadcast Address = 192.168.1.255
Option: (28) Broadcast Address
Length: 4
Value: c0a801ff
Option: (t=3,l=4) Router = 192.168.1.1
Option: (3) Router
Length: 4
Value: c0a80101
Option: (t=15,l=24) Domain Name = "panayk.endofinternet.org"
Option: (15) Domain Name
Length: 24
Value: 70616e61796b2e656e646f66696e7465726e65742e6f7267
Option: (t=6,l=4) Domain Name Server = 192.168.1.10
Option: (6) Domain Name Server
Length: 4
Value: c0a8010a
Option: (t=44,l=4) NetBIOS over TCP/IP Name Server = 192.168.1.1
Option: (44) NetBIOS over TCP/IP Name Server
Length: 4
Value: c0a80101
End Option

0000 98 fc 11 d5 7b 76 00 16 e6 3b c3 e9 08 00 45 00 ....{v...;....E.
0010 01 54 00 00 40 00 40 11 b6 3d c0 a8 01 0a c0 a8 .T..@.@..=......
0020 01 01 00 43 00 43 01 40 ec 0a 02 01 06 01 df 8b ...C.C.@........
0030 6c 3b 00 12 00 00 00 00 00 00 c0 a8 01 0c 00 00 l;..............
0040 00 00 c0 a8 01 01 5a 6d 8f a7 9a 56 00 00 00 00 ......Zm...V....
0050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0080 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0090 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00e0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0100 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0110 00 00 00 00 00 00 63 82 53 63 35 01 02 36 04 c0 ......c.Sc5..6..
0120 a8 01 0a 33 04 00 00 a8 c0 01 04 ff ff ff 00 1c ...3............
0130 04 c0 a8 01 ff 03 04 c0 a8 01 01 0f 18 70 61 6e .............pan
0140 61 79 6b 2e 65 6e 64 6f 66 69 6e 74 65 72 6e 65 ayk.endofinterne
0150 74 2e 6f 72 67 06 04 c0 a8 01 0a 2c 04 c0 a8 01 t.org......,....
0160 01 ff ..
No. Time Source Destination Protocol Length Info
369 6.835836 192.168.1.1 192.168.1.10 DHCP 354 DHCP Offer - Transaction ID 0xdf8b6c3b

Frame 369: 354 bytes on wire (2832 bits), 354 bytes captured (2832 bits)
Arrival Time: May 15, 2012 15:51:36.396886000 EEST
Epoch Time: 1337086296.396886000 seconds
[Time delta from previous captured frame: 0.002268000 seconds]
[Time delta from previous displayed frame: 0.002268000 seconds]
[Time since reference or first frame: 6.835836000 seconds]
Frame Number: 369
Frame Length: 354 bytes (2832 bits)
Capture Length: 354 bytes (2832 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: eth:ip:udp:bootp]
[Coloring Rule Name: UDP]
[Coloring Rule String: udp]
Ethernet II, Src: Cisco-Li_d5:7b:76 (98:fc:11:d5:7b:76), Dst: Giga-Byt_3b:c3:e9 (00:16:e6:3b:c3:e9)
Destination: Giga-Byt_3b:c3:e9 (00:16:e6:3b:c3:e9)
Address: Giga-Byt_3b:c3:e9 (00:16:e6:3b:c3:e9)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Source: Cisco-Li_d5:7b:76 (98:fc:11:d5:7b:76)
Address: Cisco-Li_d5:7b:76 (98:fc:11:d5:7b:76)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Type: IP (0x0800)
Internet Protocol Version 4, Src: 192.168.1.1 (192.168.1.1), Dst: 192.168.1.10 (192.168.1.10)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))
0000 00.. = Differentiated Services Codepoint: Default (0x00)
.... ..00 = Explicit Congestion Notification: Not-ECT (Not ECN-Capable Transport) (0x00)
Total Length: 340
Identification: 0x0000 (0)
Flags: 0x02 (Don't Fragment)
0... .... = Reserved bit: Not set
.1.. .... = Don't fragment: Set
..0. .... = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: UDP (17)
Header checksum: 0xb63d [correct]
[Good: True]
[Bad: False]
Source: 192.168.1.1 (192.168.1.1)
Destination: 192.168.1.10 (192.168.1.10)
User Datagram Protocol, Src Port: bootps (67), Dst Port: bootps (67)
Source port: bootps (67)
Destination port: bootps (67)
Length: 320
Checksum: 0xec09 [validation disabled]
[Good Checksum: False]
[Bad Checksum: False]
Bootstrap Protocol
Message type: Boot Reply (2)
Hardware type: Ethernet
Hardware address length: 6
Hops: 2
Transaction ID: 0xdf8b6c3b
Seconds elapsed: 18
Bootp flags: 0x0000 (Unicast)
0... .... .... .... = Broadcast flag: Unicast
.000 0000 0000 0000 = Reserved flags: 0x0000
Client IP address: 0.0.0.0 (0.0.0.0)
Your (client) IP address: 192.168.1.12 (192.168.1.12)
Next server IP address: 0.0.0.0 (0.0.0.0)
Relay agent IP address: 192.168.1.1 (192.168.1.1)
Client MAC address: 5a:6d:8f:a7:9a:56 (5a:6d:8f:a7:9a:56)
Client hardware address padding: 00000000000000000000
Server host name not given
Boot file name not given
Magic cookie: DHCP
Option: (t=53,l=1) DHCP Message Type = DHCP Offer
Option: (53) DHCP Message Type
Length: 1
Value: 02
Option: (t=54,l=4) DHCP Server Identifier = 192.168.1.10
Option: (54) DHCP Server Identifier
Length: 4
Value: c0a8010a
Option: (t=51,l=4) IP Address Lease Time = 12 hours
Option: (51) IP Address Lease Time
Length: 4
Value: 0000a8c0
Option: (t=1,l=4) Subnet Mask = 255.255.255.0
Option: (1) Subnet Mask
Length: 4
Value: ffffff00
Option: (t=28,l=4) Broadcast Address = 192.168.1.255
Option: (28) Broadcast Address
Length: 4
Value: c0a801ff
Option: (t=3,l=4) Router = 192.168.1.1
Option: (3) Router
Length: 4
Value: c0a80101
Option: (t=15,l=24) Domain Name = "panayk.endofinternet.org"
Option: (15) Domain Name
Length: 24
Value: 70616e61796b2e656e646f66696e7465726e65742e6f7267
Option: (t=6,l=4) Domain Name Server = 192.168.1.10
Option: (6) Domain Name Server
Length: 4
Value: c0a8010a
Option: (t=44,l=4) NetBIOS over TCP/IP Name Server = 192.168.1.1
Option: (44) NetBIOS over TCP/IP Name Server
Length: 4
Value: c0a80101
End Option

0000 00 16 e6 3b c3 e9 98 fc 11 d5 7b 76 08 00 45 00 ...;......{v..E.
0010 01 54 00 00 40 00 40 11 b6 3d c0 a8 01 01 c0 a8 .T..@.@..=......
0020 01 0a 00 43 00 43 01 40 ec 09 02 01 06 02 df 8b ...C.C.@........
0030 6c 3b 00 12 00 00 00 00 00 00 c0 a8 01 0c 00 00 l;..............
0040 00 00 c0 a8 01 01 5a 6d 8f a7 9a 56 00 00 00 00 ......Zm...V....
0050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0080 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0090 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00e0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0100 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0110 00 00 00 00 00 00 63 82 53 63 35 01 02 36 04 c0 ......c.Sc5..6..
0120 a8 01 0a 33 04 00 00 a8 c0 01 04 ff ff ff 00 1c ...3............
0130 04 c0 a8 01 ff 03 04 c0 a8 01 01 0f 18 70 61 6e .............pan
0140 61 79 6b 2e 65 6e 64 6f 66 69 6e 74 65 72 6e 65 ayk.endofinterne
0150 74 2e 6f 72 67 06 04 c0 a8 01 0a 2c 04 c0 a8 01 t.org......,....
0160 01 ff ..
 
Old 05-15-2012, 01:51 PM
Panayiotis Karabassis
 
Default strangeness with dhcp relay server

I had some insight from the Cisco support forums. Apparently DHCP Relays
are meant to forward requests *outside* the LAN, and should not be used
when server and relay are in the same LAN. So I am guessing the behavior
is not defined, if this happens.

The thread is here:

http://homecommunity.cisco.com/t5/Wireless-Routers/Strange-problem-with-X3000-DHCP-Relay-functionality/td-p/519783

I really don't know the first thing about networking... :-)

On 15/05/2012 04:12 μμ, Panayiotis Karabassis wrote:
> Hiya,
>
> I had posted a while back about this problem, and it seems critical
> information was under my nose.
>
> I am running my own dhcpd server on my Debian box. Often a client would
> send DISCOVER packets, but receive no reply. The information comes from
> wireshark running on the server machine, and I attach the relevant packets.
>
> My network is:
>
> DHCP server (wheezy)
> <--(wifi)-->
> Linksys X3000 router acting as a DHCP relay
> <--(wifi)-->
> Linksys RE1000 repeater
> <--(wifi)-->
> client machine
>
> As you can see the DHCP server receives the DISCOVER message and replies
> with an OFFER message to the router (relay). And then the router sends
> the OFFER back to the server instead of the client!
>
> Linksys is a good company as far as I know, so this must be my fault.
> Does anyone have any ideas?
>
> Best regards and thanks,
> Panayiotis


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Old 05-16-2012, 08:33 AM
Andrei POPESCU
 
Default strangeness with dhcp relay server

On Ma, 15 mai 12, 16:51:02, Panayiotis Karabassis wrote:
> I had some insight from the Cisco support forums. Apparently DHCP Relays
> are meant to forward requests *outside* the LAN, and should not be used
> when server and relay are in the same LAN. So I am guessing the behavior
> is not defined, if this happens.

Well, then don't use DHCP Relay

Seriously, whenever I used some other machine as DHCP server all I ever
did was disable DHCP in the box and everything just worked (this with a
wide variety of brands).

Kind regards,
Andrei
--
Offtopic discussions among Debian users and developers:
http://lists.alioth.debian.org/mailman/listinfo/d-community-offtopic
 
Old 05-16-2012, 09:06 PM
Panayiotis Karabassis
 
Default strangeness with dhcp relay server

On 16/05/2012 11:33 πμ, Andrei POPESCU wrote:
> On Ma, 15 mai 12, 16:51:02, Panayiotis Karabassis wrote:
>> I had some insight from the Cisco support forums. Apparently DHCP Relays
>> are meant to forward requests *outside* the LAN, and should not be used
>> when server and relay are in the same LAN. So I am guessing the behavior
>> is not defined, if this happens.
> Well, then don't use DHCP Relay

Haha, exactly what I did. ;-)
> Seriously, whenever I used some other machine as DHCP server all I ever
> did was disable DHCP in the box and everything just worked (this with a
> wide variety of brands).

It worked for about an hour, now the packets don't arrive at the server
at all ...except if I reconfigure the network interface on the server,
which buys another hour. Not very automagical. :-)

I am pursuing this on the CISCO forums. I think it must be a problem
with the routing of messages. Other traffic works perfectly. UDP
delivery is not guaranteed but shouldn't at least one packet out of a
dozen arrive? I even tried to set aside 14 Mbps for DHCP using tcng
(Traffic Control Next Generation) but no luck. Something along the way
must be blocking the packets. Perhaps the router thinks the packets are
needless or part of a network attack?

Perhaps I should install one of the Free firmwares to do some
packet-capturing.

I will post back, if I get to the end.

> Kind regards,
> Andrei

Thanks. Likewise ;-)
Panayiotis


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