Alcatel Carrier Internetworking Solutions 6648 User Manual
Troubleshooting BOOTP/DHCP/UDP Relay
Starting the Troubleshooting Procedure
OmniSwitch Troubleshooting Guide
September 2005
page 5-3
Preliminary
6/5/06
Forward Delay Timer
Forward delay is the amount of time in seconds UDP relay will wait before forwarding a request to a
DHCP server, or the same DHCP server. (If only one is configured on the switch.) This allows the DHCP
server who initially got the DHCP request packet from the client to respond before the request is
forwarded to another DHCP server.
DHCP server, or the same DHCP server. (If only one is configured on the switch.) This allows the DHCP
server who initially got the DHCP request packet from the client to respond before the request is
forwarded to another DHCP server.
Additionally, the relay agent uses the forward delay value to determine if the client has waited long
enough before sending another DHCP request. The relay agent will discard the DHCP request packet sent
by the client if the delay variable in the DHCP request packet is less than the forward delay time.
enough before sending another DHCP request. The relay agent will discard the DHCP request packet sent
by the client if the delay variable in the DHCP request packet is less than the forward delay time.
Please note that the show ip helper CLI command is a universal command. It applies for all DHCP
server(s) configured on the switch.
server(s) configured on the switch.
Maximum number of hops
This value lists the maximum number of relays/hops a DHCP request packet will pass through before
being discarded. This prevents a DHCP request packet from looping through a network. A DHCP request
packet will be discarded if its hop count is greater than or equal to the maximum number of hops.
being discarded. This prevents a DHCP request packet from looping through a network. A DHCP request
packet will be discarded if its hop count is greater than or equal to the maximum number of hops.
Displaying DHCP Statistics
The show ip helper stats CLI command lists the total number of DHCP packets sent by both the client
and the server. It also lists forward delay violations and violations for maximum hop count. This command
is especially useful to determine if the client is not incrementing its forward delay variable or if DHCP
request packets are looping through the network. And it also gives you a clear sense if the UDP Relay
agent is forwarding packets to or from either the client or the server. If there are incrementing Delay of
Hops Violations, this would explain why a pc is unable to get a DHCP address. A sniffer trace would be
useful in this instance.
and the server. It also lists forward delay violations and violations for maximum hop count. This command
is especially useful to determine if the client is not incrementing its forward delay variable or if DHCP
request packets are looping through the network. And it also gives you a clear sense if the UDP Relay
agent is forwarding packets to or from either the client or the server. If there are incrementing Delay of
Hops Violations, this would explain why a pc is unable to get a DHCP address. A sniffer trace would be
useful in this instance.
The following is an example of the show ip helper stats CLI command:
-> show ip helper stats
Global Statistics :
Global Statistics :
Reception From Client :
Total Count = 567, Delta = 66,
Forw Delay Violation :
Total Count = 18, Delta = 10,
Max Hops Violation :
Total Count = 0, Delta = 0,
Server Specific Statistics :
Server 10.10.10.58
Tx Server :
Total Count = 31, Delta = 28
Note. See the “DHCP Relay Commands” chapter in the OmniSwitch CLI Reference Guide for more infor-
mation.
mation.