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DHCP Offer Wrong Interface

Hello,

I have a issue with DHCP Request/Offer.

My setup is One interface (LAN) the same interface have vlan for Wifi. When a device ask for dhcp request it com in to the good interface but the respond (out)is going on both interface.

My tcpdump in the firewall is that if i do a request.

It only happen when AP is doing that, my VM that is on another vlan seem to be good.

Note that i also try another AP from another provider and doing same thing at the reply dhcp.

10:39:01.610228 Port1.105, IN: IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 34:97:f6:7c:b5:fc, length 314
10:39:01.610331 Port1, OUT: IP 192.168.123.1.67 > 192.168.123.100.68: BOOTP/DHCP, Reply, length 300
10:39:01.616808 Port1.105, IN: IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 34:97:f6:7c:b5:fc, length 326
10:39:01.821469 Port1.105, OUT: IP 192.168.105.1.67 > 192.168.105.100.68: BOOTP/DHCP, Reply, length 300
10:39:01.926434 Port1, OUT: IP 192.168.123.1.67 > 192.168.123.100.68: BOOTP/DHCP, Reply, length 300
10:39:02.015611 Port1.105, OUT: IP 192.168.105.1.67 > 255.255.255.255.68: BOOTP/DHCP, Reply, length 300

All DHCP is inside Sophos XG.

Another things, if i do wireshark on my pc locate at subnet 123 i detect dhcp offer but not the request.

that mean the AP seem to send the request in the correct vlan.

Does someone have any idea? That is could be a bug inside the dhcp?

Thank you

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0 Skyboo over 7 years ago

Another Detail

When i go in the ARP it's show incomplete.

I did see what could be wrong in the switch event on AP.

It's seem to point with sophos that does not send packet correctly.

Help will be appreciated.

thanks all
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0 lferrara over 7 years ago in reply to Skyboo

Skyboo,

can you share the DHCP configuration from XG UI?

Thanks
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0 Skyboo over 7 years ago in reply to lferrara

I also test with relay option and same issue.

My pc in LAN is receiving the dhcp (wireshark).

I also have some reservation in the pool.

I use the vlan 106 to test because the 105 is need to work correctly.

the AP is also in vlan 1 for management and wifi is all tag.
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0 lferrara over 7 years ago in reply to Skyboo

Skyboo,

both VLAN 1 and VLAN 106 have the same IP address. This is the issue. DHCP relay and DHCP server must act on different networks.

Regards
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0 Skyboo over 7 years ago in reply to lferrara

Forget about the relay.

before i set the relay the 106 as internal in the sophos and i have the same issue.

see bellow
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0 lferrara over 7 years ago in reply to Skyboo

Skyboo,

please open a ticket with support.

Let us know.

sachingurung can you investigate in LAB this behavior? It should be very easy to simulate it.

Thanks
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0 sachingurung over 7 years ago in reply to Skyboo

Hi Skyboo,

Go to Advance Console and send me a capture of the following command:

tcpdump -nei any port 67 or port 68

The packets should be tagged with ethertype 801.q as every VLAN is a separate broadcast domain, the packet arriving on the XG interface should be tagged which will tell the firewall to forward it on the respective VLAN interface. Here, I don't see the tagged packet in the dumps.

Thanks
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0 sachingurung over 7 years ago in reply to Skyboo

Hi Skyboo,

Go to Advance Console and send me a capture of the following command:

tcpdump -nei any port 67 or port 68

The packets should be tagged with ethertype 801.q as every VLAN is a separate broadcast domain, the packet arriving on the XG interface should be tagged which will tell the firewall to forward it on the respective VLAN interface. Here, I don't see the tagged packet in the dumps.

Thanks
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0 Skyboo over 7 years ago in reply to sachingurung

Hi,

i try you command but a something wrong with the parameter.

i try with port only

i just try one dhcp request at this time and i think i get good ip but when you see the output is clear that is something wrong.

one thing that i not mention, event if i disable the dhcp in this vlan 106 i get the ip of the other vlan.

I can try it if you need.

Let me know if you need more details.

I really try few things event activate the ip spoofing but does not help at all.

Thanks

console> tcpdump 'port 67 or port 68'
tcpdump: Starting Packet Dump
22:17:02.554047 Port1.106, IN: IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 34:97:f6:7c:b5:fc, length 314
22:17:03.739452 Port1, OUT: IP 192.168.123.1.67 > 192.168.123.112.68: BOOTP/DHCP, Reply, length 300
22:17:03.758607 Port1, IN:   B 34:97:f6:7c:b5:fc ethertype Unknown (0x006a), length 374:
        0x0000: 0000 0800 4510 0162 0000 4000 4011 397c ....E..b..@.@.9|
        0x0010: 0000 0000 ffff ffff 0044 0043 014e e454 .........D.C.N.T
        0x0020: 0101 0600 22c1 4dd8 0008 0000 0000 0000 ....".M.........
        0x0030: 0000 0000 0000 0000 0000 0000 3497 f67c ............4..|
        0x0040: b5fc 0000 0000 0000 0000 0000 0000 0000 ................
22:17:03.758607 Port1.106, IN: IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 34:97:f6:7c:b5:fc, length 326
22:17:03.932516 Port1, OUT: IP 192.168.123.1.67 > 192.168.123.112.68: BOOTP/DHCP, Reply, length 300
22:17:04.019939 Port1.106, OUT: IP 192.168.106.1.67 > 255.255.255.255.68: BOOTP/DHCP, Reply, length 300
22:17:04.019945 Port1, OUT: Out 00:ae:2a:df:04:01 ethertype Unknown (0x006a), length 348:
        0x0000: 0000 0800 4510 0148 0000 0000 8011 0eec ....E..H........
        0x0010: c0a8 6a01 ffff ffff 0043 0044 0134 92dd ..j......C.D.4..
        0x0020: 0201 0600 22c1 4dd8 0008 8000 0000 0000 ....".M.........
        0x0030: 0000 0000 c0a8 6a01 0000 0000 3497 f67c ......j.....4..|
        0x0040: b5fc 0000 0000 0000 0000 0000 0000 0000 ................
22:17:04.019980 Port1.106, OUT: IP 192.168.106.1.67 > 192.168.106.101.68: BOOTP/DHCP, Reply, length 300
22:17:04.019981 Port1, OUT: Out 00:ae:2a:df:04:01 ethertype Unknown (0x006a), length 348:
        0x0000: 0000 0800 4510 0148 0000 0000 8011 e3dd ....E..H........
        0x0010: c0a8 6a01 c0a8 6a65 0043 0044 0134 9e5d ..j...je.C.D.4.]
        0x0020: 0201 0600 22c1 4dd8 0007 0000 0000 0000 ....".M.........
        0x0030: c0a8 6a65 0000 0000 0000 0000 3497 f67c ..je........4..|
        0x0040: b5fc 0000 0000 0000 0000 0000 0000 0000 ................
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0 lferrara over 7 years ago in reply to Skyboo

Skyboo,

the command must be launched from advanced shell. Connect to XG console, option 5 and then 3.

Regards
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0 Skyboo over 7 years ago in reply to lferrara

Hi,

Sorry my mistake

I verify and i get 192.168.123.112 that is the wrong IP for this wifi.

My AP is a tplink eap225, before i have the 901 version.

I also test in the past week a Mikrotik device and it seem to doing that with all ap.

Thanks

19:10:26.406404 Port1, IN:   B 34:97:f6:7c:b5:fc ethertype Unknown (0x006a), length 362:
        0x0000: 0000 0800 4510 0156 0000 4000 4011 3988 ....E..V..@.@.9.
        0x0010: 0000 0000 ffff ffff 0044 0043 0142 94db .........D.C.B..
        0x0020: 0101 0600 aa3e f7bf 0000 0000 0000 0000 .....>..........
        0x0030: 0000 0000 0000 0000 0000 0000 3497 f67c ............4..|
        0x0040: b5fc 0000 0000 0000 0000 0000 0000 0000 ................
19:10:26.406404 Port1.106, IN:   B 34:97:f6:7c:b5:fc ethertype IPv4 (0x0800), length 358: 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 34:97:f6:7c:b5:fc, length 314
19:10:27.595455 Port1, OUT: Out 00:ae:2a:df:04:01 ethertype IPv4 (0x0800), length 344: 192.168.123.1.67 > 192.168.123.112.68: BOOTP/DHCP, Reply, length 300
19:10:27.610620 Port1, IN:   B 34:97:f6:7c:b5:fc ethertype Unknown (0x006a), length 374:
        0x0000: 0000 0800 4510 0162 0000 4000 4011 397c ....E..b..@.@.9|
        0x0010: 0000 0000 ffff ffff 0044 0043 014e b2f6 .........D.C.N..
        0x0020: 0101 0600 aa3e f7bf 0001 0000 0000 0000 .....>..........
        0x0030: 0000 0000 0000 0000 0000 0000 3497 f67c ............4..|
        0x0040: b5fc 0000 0000 0000 0000 0000 0000 0000 ................
19:10:27.610620 Port1.106, IN:   B 34:97:f6:7c:b5:fc ethertype IPv4 (0x0800), length 370: 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 34:97:f6:7c:b5:fc, length 326
19:10:27.789391 Port1, OUT: Out 00:ae:2a:df:04:01 ethertype IPv4 (0x0800), length 344: 192.168.123.1.67 > 192.168.123.112.68: BOOTP/DHCP, Reply, length 300
19:10:27.878116 Port1.106, OUT: Out 00:ae:2a:df:04:01 ethertype IPv4 (0x0800), length 344: 192.168.106.1.67 > 255.255.255.255.68: BOOTP/DHCP, Reply, length 300
19:10:27.878121 Port1, OUT: Out 00:ae:2a:df:04:01 ethertype Unknown (0x006a), length 348:
        0x0000: 0000 0800 4510 0148 0000 0000 8011 0eec ....E..H........
        0x0010: c0a8 6a01 ffff ffff 0043 0044 0134 617f ..j......C.D.4a.
        0x0020: 0201 0600 aa3e f7bf 0001 8000 0000 0000 .....>..........
        0x0030: 0000 0000 c0a8 6a01 0000 0000 3497 f67c ......j.....4..|
        0x0040: b5fc 0000 0000 0000 0000 0000 0000 0000 ................
19:10:27.878155 Port1.106, OUT: Out 00:ae:2a:df:04:01 ethertype IPv4 (0x0800), length 344: 192.168.106.1.67 > 192.168.106.101.68: BOOTP/DHCP, Reply, length 300
19:10:27.878157 Port1, OUT: Out 00:ae:2a:df:04:01 ethertype Unknown (0x006a), length 348:
        0x0000: 0000 0800 4510 0148 0000 0000 8011 e3dd ....E..H........
        0x0010: c0a8 6a01 c0a8 6a65 0043 0044 0134 6cff ..j...je.C.D.4l.
        0x0020: 0201 0600 aa3e f7bf 0000 0000 0000 0000 .....>..........
        0x0030: c0a8 6a65 0000 0000 0000 0000 3497 f67c ..je........4..|
        0x0040: b5fc 0000 0000 0000 0000 0000 0000 0000 ................
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0 sachingurung over 7 years ago in reply to Skyboo

Hi Skyboo,

I will DM you to investigate this further.
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