DHCP Relay agent - Duplicating messages

[Gero Palacio]

Hi All,

I found a weird behavior on the DHCP relay agent which is duplicating the outgoing messages from the client when it's not supposed to.

This is the set up:

[client] <-> (192.168.1.1) [relay_agent] (10.0.0.1) <-> [pair of failover servers](10.0.1.10 & 10.0.1.11)

What I found is this:

No.  Source        Destination    Info

-- We're good here. Relay agent duplicate the discovery messages

-- to send to both pair of servers                 

44  10.0.0.1       10.0.1.11      DHCP Discover - Transaction ID 0xd2728f7c

45  10.0.0.1       10.0.1.10      DHCP Discover - Transaction ID 0xd2728f7c

  

-- Receives only 1 response from 1 of the servers. So far, so good.

47  10.0.1.10      192.168.1.1    DHCP Offer    - Transaction ID 0xd2728f7c

-- This bit is also okay. Client broadcasts the request message

-- relay agent sends 2 messages (one to each server)

-- receives only 1 response (good).

48  10.0.0.1       10.0.1.11      DHCP Request  - Transaction ID 0xd2728f7c

49  10.0.0.1       10.0.1.10      DHCP Request  - Transaction ID 0xd2728f7c

50  10.0.1.10      192.168.1.1    DHCP ACK      - Transaction ID 0xd2728f7c

-- This is the part where it gets weird. 

-- Client sends 1 requst (WireShark on the client confirms this, not shown)  

-- This message contains:

-- Relay agent IP address: 0.0.0.0 (0.0.0.0)                              

52  192.168.1.60   10.0.1.10      DHCP Request  - Transaction ID 0xd2728f7c

-- Relay agent (source 10.0.0.1) makes 4 messages!! I dont get this part

-- These 2 messages contains:

-- Relay agent IP address: 192.168.1.1 (192.168.1.1) ???

53  10.0.0.1       10.0.1.11      DHCP Request  - Transaction ID 0xd2728f7c

54  10.0.0.1       10.0.1.10      DHCP Request  - Transaction ID 0xd2728f7c

-- These 2:

-- Relay agent IP address: 10.0.0.1 (10.0.0.1) ???

55  10.0.0.1       10.0.1.11      DHCP Request  - Transaction ID 0xd2728f7c

56  10.0.0.1       10.0.1.10      DHCP Request  - Transaction ID 0xd2728f7c

                                                  

-- The response are received with the client ip and with 

-- the relay agent ip that's facing the client                             

57  10.0.1.11      192.168.1.1    DHCP ACK      - Transaction ID 0xd2728f7c

58  10.0.1.10      192.168.1.60   DHCP ACK      - Transaction ID 0xd2728f7c

59  10.0.1.10      192.168.1.1    DHCP ACK      - Transaction ID 0xd2728f7c

Why is this happening? Why is the DHCP Relay Agent IP is changing in the DHCP message?
I've read the DHCP Handbook chapters discussing relay agents (Ch 7 and 9) and also the chapter that describes the ISC relay agent but it doesn't seem to behave in that way.

I'm using version 4.2.8

Thanks for your help.
Gero.

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[Gero Palacio]

Hi,

I've done further testing and it's seems that the problem is that the DHCPREQUEST unicast messages are being duplicated by the relay agent which is running on the router that connects the client subnet to the server subnet.

I also found and old thread (link here) which reports there very same problem. The person who started that thread already filled a bug report (ISC-Bugs #29053) but I was not able to find in the release notes if this problem was fixed.

I'm running DHCP v 2.4.8. Any help would be appreciated. Thanks. Gero.

On Mon, Jun 29, 2015 at 7:12 PM, Gero Palacio <[hidden email]> wrote:

Hi All,

I found a weird behavior on the DHCP relay agent which is duplicating the outgoing messages from the client when it's not supposed to.

This is the set up:

[client] <-> (192.168.1.1) [relay_agent] (10.0.0.1) <-> [pair of failover servers](10.0.1.10 & 10.0.1.11)

What I found is this:

No.  Source        Destination    Info

-- We're good here. Relay agent duplicate the discovery messages

-- to send to both pair of servers                 

44  10.0.0.1       10.0.1.11      DHCP Discover - Transaction ID 0xd2728f7c

45  10.0.0.1       10.0.1.10      DHCP Discover - Transaction ID 0xd2728f7c

  

-- Receives only 1 response from 1 of the servers. So far, so good.

47  10.0.1.10      192.168.1.1    DHCP Offer    - Transaction ID 0xd2728f7c

-- This bit is also okay. Client broadcasts the request message

-- relay agent sends 2 messages (one to each server)

-- receives only 1 response (good).

48  10.0.0.1       10.0.1.11      DHCP Request  - Transaction ID 0xd2728f7c

49  10.0.0.1       10.0.1.10      DHCP Request  - Transaction ID 0xd2728f7c

50  10.0.1.10      192.168.1.1    DHCP ACK      - Transaction ID 0xd2728f7c

-- This is the part where it gets weird. 

-- Client sends 1 requst (WireShark on the client confirms this, not shown)  

-- This message contains:

-- Relay agent IP address: 0.0.0.0 (0.0.0.0)                              

52  192.168.1.60   10.0.1.10      DHCP Request  - Transaction ID 0xd2728f7c

-- Relay agent (source 10.0.0.1) makes 4 messages!! I dont get this part

-- These 2 messages contains:

-- Relay agent IP address: 192.168.1.1 (192.168.1.1) ???

53  10.0.0.1       10.0.1.11      DHCP Request  - Transaction ID 0xd2728f7c

54  10.0.0.1       10.0.1.10      DHCP Request  - Transaction ID 0xd2728f7c

-- These 2:

-- Relay agent IP address: 10.0.0.1 (10.0.0.1) ???

55  10.0.0.1       10.0.1.11      DHCP Request  - Transaction ID 0xd2728f7c

56  10.0.0.1       10.0.1.10      DHCP Request  - Transaction ID 0xd2728f7c

                                                  

-- The response are received with the client ip and with 

-- the relay agent ip that's facing the client                             

57  10.0.1.11      192.168.1.1    DHCP ACK      - Transaction ID 0xd2728f7c

58  10.0.1.10      192.168.1.60   DHCP ACK      - Transaction ID 0xd2728f7c

59  10.0.1.10      192.168.1.1    DHCP ACK      - Transaction ID 0xd2728f7c

Why is this happening? Why is the DHCP Relay Agent IP is changing in the DHCP message?
I've read the DHCP Handbook chapters discussing relay agents (Ch 7 and 9) and also the chapter that describes the ISC relay agent but it doesn't seem to behave in that way.

I'm using version 4.2.8

Thanks for your help.
Gero.

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dhcp-users mailing list
[hidden email]
https://lists.isc.org/mailman/listinfo/dhcp-users

[Gero Palacio]

Correction: ISC DHCP v 4.2.8

On Tue, Jun 30, 2015 at 1:45 PM, Gero Palacio <[hidden email]> wrote:

Hi,

I've done further testing and it's seems that the problem is that the DHCPREQUEST unicast messages are being duplicated by the relay agent which is running on the router that connects the client subnet to the server subnet.

I also found and old thread (link here) which reports there very same problem. The person who started that thread already filled a bug report (ISC-Bugs #29053) but I was not able to find in the release notes if this problem was fixed.

I'm running DHCP v 2.4.8. Any help would be appreciated. Thanks. Gero.

On Mon, Jun 29, 2015 at 7:12 PM, Gero Palacio <[hidden email]> wrote:

Hi All,

I found a weird behavior on the DHCP relay agent which is duplicating the outgoing messages from the client when it's not supposed to.

This is the set up:

[client] <-> (192.168.1.1) [relay_agent] (10.0.0.1) <-> [pair of failover servers](10.0.1.10 & 10.0.1.11)

What I found is this:

No.  Source        Destination    Info

-- We're good here. Relay agent duplicate the discovery messages

-- to send to both pair of servers                 

44  10.0.0.1       10.0.1.11      DHCP Discover - Transaction ID 0xd2728f7c

45  10.0.0.1       10.0.1.10      DHCP Discover - Transaction ID 0xd2728f7c

  

-- Receives only 1 response from 1 of the servers. So far, so good.

47  10.0.1.10      192.168.1.1    DHCP Offer    - Transaction ID 0xd2728f7c

-- This bit is also okay. Client broadcasts the request message

-- relay agent sends 2 messages (one to each server)

-- receives only 1 response (good).

48  10.0.0.1       10.0.1.11      DHCP Request  - Transaction ID 0xd2728f7c

49  10.0.0.1       10.0.1.10      DHCP Request  - Transaction ID 0xd2728f7c

50  10.0.1.10      192.168.1.1    DHCP ACK      - Transaction ID 0xd2728f7c

-- This is the part where it gets weird. 

-- Client sends 1 requst (WireShark on the client confirms this, not shown)  

-- This message contains:

-- Relay agent IP address: 0.0.0.0 (0.0.0.0)                              

52  192.168.1.60   10.0.1.10      DHCP Request  - Transaction ID 0xd2728f7c

-- Relay agent (source 10.0.0.1) makes 4 messages!! I dont get this part

-- These 2 messages contains:

-- Relay agent IP address: 192.168.1.1 (192.168.1.1) ???

53  10.0.0.1       10.0.1.11      DHCP Request  - Transaction ID 0xd2728f7c

54  10.0.0.1       10.0.1.10      DHCP Request  - Transaction ID 0xd2728f7c

-- These 2:

-- Relay agent IP address: 10.0.0.1 (10.0.0.1) ???

55  10.0.0.1       10.0.1.11      DHCP Request  - Transaction ID 0xd2728f7c

56  10.0.0.1       10.0.1.10      DHCP Request  - Transaction ID 0xd2728f7c

                                                  

-- The response are received with the client ip and with 

-- the relay agent ip that's facing the client                             

57  10.0.1.11      192.168.1.1    DHCP ACK      - Transaction ID 0xd2728f7c

58  10.0.1.10      192.168.1.60   DHCP ACK      - Transaction ID 0xd2728f7c

59  10.0.1.10      192.168.1.1    DHCP ACK      - Transaction ID 0xd2728f7c

Why is this happening? Why is the DHCP Relay Agent IP is changing in the DHCP message?
I've read the DHCP Handbook chapters discussing relay agents (Ch 7 and 9) and also the chapter that describes the ISC relay agent but it doesn't seem to behave in that way.

I'm using version 4.2.8

Thanks for your help.
Gero.

_______________________________________________
dhcp-users mailing list
[hidden email]
https://lists.isc.org/mailman/listinfo/dhcp-users