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Strange behaviour on 3com 5500G used as an DHCP relay

steverding
Occasional Visitor

Strange behaviour on 3com 5500G used as an DHCP relay

I have some vlan interfaces on my 3 com 5500G. I want to use the switch as an DHCP relay to relay DHCP requests to a DHCP server from those vlans. 

 

Everytime a client requests an ip  address the request is relayed to the dhcp server and an address is given to the client. Excactly one minute after that, the 5500G sends a DHCP REQUEST for the exact same address that is NAKed by the DHCP server. The switch now keeps requesting this ip address (that has allready been given to the client). 

 

I attached log output and network dumps from the dhcp server. Maybe somebody can explain, what goes wrong

 


##This is the request from the real client:
Feb  2 10:24:09 lan-gw dhcpd: DHCPREQUEST for 10.88.128.11 from 00:0b:5d:93:c1:28 (notebook) via eth0
Feb  2 10:24:09 lan-gw dhcpd: DHCPACK on 10.88.128.11 to 00:0b:5d:93:c1:28 (notebook) via eth0

##Here comes the switch :

Feb  2 10:24:25 lan-gw dhcpd: DHCPREQUEST for 10.88.128.11 from 00:1e:c1:73:b5:00 via 10.88.128.1: lease 10.88.128.11 unavailable.
Feb  2 10:24:25 lan-gw dhcpd: DHCPNAK on 10.88.128.11 to 00:1e:c1:73:b5:00 via 10.88.128.1

##And the switch does it again and again
Feb  2 10:25:25 lan-gw dhcpd: DHCPREQUEST for 10.88.128.11 from 00:1e:c1:73:b5:00 via 10.88.128.1: lease 10.88.128.11 unavailable.
Feb  2 10:25:25 lan-gw dhcpd: DHCPNAK on 10.88.128.11 to 00:1e:c1:73:b5:00 via 10.88.128.1
Feb  2 10:26:25 lan-gw dhcpd: DHCPREQUEST for 10.88.128.11 from 00:1e:c1:73:b5:00 via 10.88.128.1: lease 10.88.128.11 unavailable.
Feb  2 10:26:25 lan-gw dhcpd: DHCPNAK on 10.88.128.11 to 00:1e:c1:73:b5:00 via 10.88.128.1
Feb  2 10:27:25 lan-gw dhcpd: DHCPREQUEST for 10.88.128.11 from 00:1e:c1:73:b5:00 via 10.88.128.1: lease 10.88.128.11 unavailable.
Feb  2 10:27:25 lan-gw dhcpd: DHCPNAK on 10.88.128.11 to 00:1e:c1:73:b5:00 via 10.88.128.1

##Here is a packet dump on the dhcp server:

root@lan-gw:~# tcpdump port 67 -vvvn
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
10:24:09.053794 IP (tos 0x0, ttl 127, id 406, offset 0, flags [none], proto UDP (17), length 328)
    10.88.128.11.68 > 10.88.132.100.67: BOOTP/DHCP, Request from 00:0b:5d:93:c1:28, length 300, xid 0x2a5ac645, Flags [none] (0x0000)
   Client-IP 10.88.128.11
   Client-Ethernet-Address 00:0b:5d:93:c1:28 [|bootp]
10:24:09.059217 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 371)
    10.88.132.100.67 > 10.88.128.11.68: BOOTP/DHCP, Reply, length 343, xid 0x2a5ac645, Flags [none] (0x0000)
   Client-IP 10.88.128.11
   Your-IP 10.88.128.11
   Server-IP 10.88.132.100
   Client-Ethernet-Address 00:0b:5d:93:c1:28 [|bootp]


10:24:25.375678 IP (tos 0x0, ttl 255, id 8456, offset 0, flags [none], proto UDP (17), length 281)
    10.88.128.1.67 > 10.88.132.100.67: BOOTP/DHCP, Request from 00:1e:c1:73:b5:00, length 253, xid 0x1, Flags [none] (0x0000)
   Client-IP 10.88.128.11
   Gateway-IP 10.88.128.1
   Client-Ethernet-Address 00:1e:c1:73:b5:00 [|bootp]
10:24:25.375934 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 328)
    10.88.132.100.67 > 10.88.128.1.67: BOOTP/DHCP, Reply, length 300, xid 0x1, Flags [Broadcast] (0x8000)
   Server-IP 10.88.132.100
   Gateway-IP 10.88.128.1
   Client-Ethernet-Address 00:1e:c1:73:b5:00 [|bootp]


10:25:25.384032 IP (tos 0x0, ttl 255, id 8483, offset 0, flags [none], proto UDP (17), length 281)
    10.88.128.1.67 > 10.88.132.100.67: BOOTP/DHCP, Request from 00:1e:c1:73:b5:00, length 253, xid 0x1, Flags [none] (0x0000)
   Client-IP 10.88.128.11
   Gateway-IP 10.88.128.1
   Client-Ethernet-Address 00:1e:c1:73:b5:00 [|bootp]
10:25:25.384273 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 328)
    10.88.132.100.67 > 10.88.128.1.67: BOOTP/DHCP, Reply, length 300, xid 0x1, Flags [Broadcast] (0x8000)
   Server-IP 10.88.132.100
   Gateway-IP 10.88.128.1
   Client-Ethernet-Address 00:1e:c1:73:b5:00 [|bootp]


10:26:25.386968 IP (tos 0x0, ttl 255, id 8494, offset 0, flags [none], proto UDP (17), length 281)
    10.88.128.1.67 > 10.88.132.100.67: BOOTP/DHCP, Request from 00:1e:c1:73:b5:00, length 253, xid 0x1, Flags [none] (0x0000)
   Client-IP 10.88.128.11
   Gateway-IP 10.88.128.1
   Client-Ethernet-Address 00:1e:c1:73:b5:00 [|bootp]
10:26:25.394076 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 328)
    10.88.132.100.67 > 10.88.128.1.67: BOOTP/DHCP, Reply, length 300, xid 0x1, Flags [Broadcast] (0x8000)
   Server-IP 10.88.132.100
   Gateway-IP 10.88.128.1
   Client-Ethernet-Address 00:1e:c1:73:b5:00 [|bootp]
10:27:25.386763 IP (tos 0x0, ttl 255, id 8503, offset 0, flags [none], proto UDP (17), length 281)
    10.88.128.1.67 > 10.88.132.100.67: BOOTP/DHCP, Request from 00:1e:c1:73:b5:00, length 253, xid 0x1, Flags [none] (0x0000)
   Client-IP 10.88.128.11
   Gateway-IP 10.88.128.1
   Client-Ethernet-Address 00:1e:c1:73:b5:00 [|bootp]
10:27:25.387250 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 328)
    10.88.132.100.67 > 10.88.128.1.67: BOOTP/DHCP, Reply, length 300, xid 0x1, Flags [Broadcast] (0x8000)
   Server-IP 10.88.132.100
   Gateway-IP 10.88.128.1
   Client-Ethernet-Address 00:1e:c1:73:b5:00 [|bootp]

 

 

P.S. This thread has been moved from Switching > Legacy to Comware-Based. - Hp Forum Moderator

 



  

4 REPLIES
sm-noc
Advisor

Re: Strange behaviour on 3com 5500G used as an DHCP relay

Hi,

 

Is the ip already reserved to a specific host? or we talking on a specific IP only, can you also post the current config of your switch

steverding
Occasional Visitor

Re: Strange behaviour on 3com 5500G used as an DHCP relay

The ip has been given to the notebook with the mac-address 00:0b:5d:93:c1:28. This can be seen on the packet dump. The same happens with every other ip and device.

My switch config is quite simple :

<5500-RZ>display dhcp-server 1
IP address of DHCP server group 1: 10.88.132.100
IP address of DHCP server group 1: 0.0.0.0
IP address of DHCP server group 1: 0.0.0.0
IP address of DHCP server group 1: 0.0.0.0
IP address of DHCP server group 1: 0.0.0.0
IP address of DHCP server group 1: 0.0.0.0
IP address of DHCP server group 1: 0.0.0.0
IP address of DHCP server group 1: 0.0.0.0
Messages from this server group: 9939
Messages to this server group: 72130
Messages from clients to this server group: 98
Messages from this server group to clients: 5830
DHCP_OFFER messages: 49
DHCP_ACK messages: 5052
DHCP_NAK messages: 4838
DHCP_DECLINE messages: 0
DHCP_DISCOVER messages: 50
DHCP_REQUEST messages: 72067
DHCP_INFORM messages: 0
DHCP_RELEASE messages: 13
BOOTP_REQUEST messages: 0
BOOTP_REPLY messages: 0


[5500-RZ-Vlan-interface51]display dhcp-server interface Vlan-interface 51
Dhcp-group 1 is configured on this interface


<5500-RZ>display interface Vlan-interface 51
Vlan-interface51 current state :UP
Line protocol current state :UP
IP Sending Frames' Format is PKTFMT_ETHNT_2, Hardware address is 001e-c173-b501
Internet Address is 10.88.128.1/23 Primary
Description : Vlan-interface51 Interface
The Maximum Transmit Unit is 1500
elvisplatini
Occasional Visitor

Re: Strange behaviour on 3com 5500G used as an DHCP relay

Hi,

 

I have the same problem on my 5500-EI switches. The switches relay the dhcp requests from the clients, but after the IP addresses have been given to the clients, the switches keeps on requesting the given addresses witch their own mac-address. Here is a small part of the dhcp server log below for one client:

 

Jun  3 07:29:54 venus dhcpd: DHCPREQUEST for 10.33.202.9 from 00:21:00:f7:fe:21 (PC3398) via 10.33.202.254
Jun  3 07:29:54 venus dhcpd: DHCPACK on 10.33.202.9 to 00:21:00:f7:fe:21 (PC3398) via 10.33.202.254
Jun  3 07:30:59 venus dhcpd: DHCPREQUEST for 10.33.202.9 from 00:24:73:45:26:40 via 10.33.202.254: lease 10.33.202.9 unavailable.
Jun  3 07:30:59 venus dhcpd: DHCPNAK on 10.33.202.9 to 00:24:73:45:26:40 via 10.33.202.254
Jun  3 07:36:37 venus dhcpd: DHCPREQUEST for 10.33.202.9 from 00:24:73:45:26:40 via 10.33.202.254: lease 10.33.202.9 unavailable.
Jun  3 07:36:37 venus dhcpd: DHCPNAK on 10.33.202.9 to 00:24:73:45:26:40 via 10.33.202.254
Jun  3 07:39:45 venus dhcpd: DHCPINFORM from 10.33.202.9 via 10.33.202.254
Jun  3 07:39:45 venus dhcpd: DHCPACK to 10.33.202.9 (00:21:00:f7:fe:21) via eth0
Jun  3 07:42:18 venus dhcpd: DHCPREQUEST for 10.33.202.9 from 00:24:73:45:26:40 via 10.33.202.254: lease 10.33.202.9 unavailable.
Jun  3 07:42:18 venus dhcpd: DHCPNAK on 10.33.202.9 to 00:24:73:45:26:40 via 10.33.202.254
Jun  3 07:47:59 venus dhcpd: DHCPREQUEST for 10.33.202.9 from 00:24:73:45:26:40 via 10.33.202.254: lease 10.33.202.9 unavailable.
Jun  3 07:47:59 venus dhcpd: DHCPNAK on 10.33.202.9 to 00:24:73:45:26:40 via 10.33.202.254

 

 

Here are the informations about the dhcp server on one of the 5500 EI

[sw1ric]display dhcp-server 0
 IP address of DHCP server group 0:   10.64.100.100
 IP address of DHCP server group 0:         0.0.0.0
 IP address of DHCP server group 0:         0.0.0.0
 IP address of DHCP server group 0:         0.0.0.0
 IP address of DHCP server group 0:         0.0.0.0
 IP address of DHCP server group 0:         0.0.0.0
 IP address of DHCP server group 0:         0.0.0.0
 IP address of DHCP server group 0:         0.0.0.0
 Messages from this server group: 1230052
 Messages to this server group: 1733567
 Messages from clients to this server group: 15933
 Messages from this server group to clients: 11849
 DHCP_OFFER messages: 2248
 DHCP_ACK messages: 9589
 DHCP_NAK messages: 1218215
 DHCP_DECLINE messages: 0
 DHCP_DISCOVER messages: 2402
 DHCP_REQUEST messages: 1727587
 DHCP_INFORM messages: 3574
 DHCP_RELEASE messages: 4
 BOOTP_REQUEST messages: 0
 BOOTP_REPLY messages: 0

 

The difference between the "Messages from clients to this server group"  and "Messages from this server group" is quite strange.

 

The manufacture information shows the switch request the IP address for its own mac address:

 

<sw1ric>dis device manuinfo
Unit 1
 First mac address    : 0024-7345-2640
 Product serial number: 9LAFBJP452640
 Product 3C number    : 3CR17161-91

 

Thanks for your ideas

 

 

 

 

 

 

 

Paulosta
Occasional Visitor

Re: Strange behaviour on 3com 5500G used as an DHCP relay

There is a paper from HP about that:

 

http://h20565.www2.hp.com/portal/site/hpsc/template.PAGE/public/kb/docDisplay/?sp4ts.oid=4174795&spf_p.tpst=kbDocDisplay&spf_p.prp_kbDocDisplay=wsrp-navigationalState%3DdocId%253Demr_na-c02601502-2%257CdocLocale%253D%257CcalledBy%253D&javax.portlet.begCacheTok=com.vignette.cachetoken&javax.portlet.endCacheTok=com.vignette.cachetoken

 

Fix:

Upgrade to Version 5.20 Release 2202P15 or later

Add to the configuration the system command:

dhcp relay hand disable 

to disable the DHCP relay handshake function that is checking the DHCP lease is still current.

Symptom:

When the Switch is acting as DHCP relay it repeatedly send requests to the DHCP server to assign the Switch addresses already assigned to clients. Each occurrence is logged by the DHCP server, filling the log.

Cause:

The switch is checking the DHCP server still has the IP Address leased to the client. This is not needed when DHCP Security is not enabled.